[PATCH 0/5] Add support for operand-specific alignment requirements

[PATCH 0/5] Add support for operand-specific alignment requirements

[Richard Sandiford]

SME has various instructions that require aligned register tuples.
However, the associated tuple modes are already widely used and do
not need to be aligned in other contexts.  It therefore isn't
appropriate to force alignment in TARGET_HARD_REGNO_MODE_OK.

There are also strided loads and stores that require:

- (regno & 0x8) == 0 for 2-register tuples
- (regno & 0xc) == 0 for 4-register tuples

Although the requirements for strided loads and stores could be
enforced by C++ conditions on the insn, it's convenient to handle
them in the same way as alignment.

This series of patches therefore adds a way for register constraints
to specify which start registers are valid and which aren't.  Most of
the details are in the covering note to the first patch.

This is clearly changing a performance-sensitive part of the compiler.
I've tried to ensure that the overhead is only small for targets that
use the new feature.  Almost all of the new code gets optimised away
on targets that don't use the feature.

Richard Sandiford (5):
  Add register filter operand to define_register_constraint
  recog: Handle register filters
  lra: Handle register filters
  ira: Handle register filters
  Add an aligned_register_operand predicate

 gcc/common.md          |  28 ++++++++
 gcc/doc/md.texi        |  41 +++++++++++-
 gcc/doc/tm.texi        |   3 +-
 gcc/doc/tm.texi.in     |   3 +-
 gcc/genconfig.cc       |   2 +
 gcc/genpreds.cc        | 146 ++++++++++++++++++++++++++++++++++++++++-
 gcc/gensupport.cc      |  48 +++++++++++++-
 gcc/gensupport.h       |   3 +
 gcc/ira-build.cc       |   8 +++
 gcc/ira-color.cc       |  10 +++
 gcc/ira-int.h          |  14 ++++
 gcc/ira-lives.cc       |  61 +++++++++++++++++
 gcc/lra-constraints.cc |  13 +++-
 gcc/recog.cc           |  14 +++-
 gcc/recog.h            |  24 ++++++-
 gcc/reginfo.cc         |   5 ++
 gcc/rtl.def            |   6 +-
 gcc/target-globals.cc  |   6 +-
 gcc/target-globals.h   |   3 +
 19 files changed, 421 insertions(+), 17 deletions(-)

-- 
2.25.1

[PATCH 1/5] Add register filter operand to define_register_constraint

[Richard Sandiford]

The main way of enforcing registers to be aligned is through
HARD_REGNO_MODE_OK.  But this is a global property that applies
to all operands.  A given (regno, mode) pair is either globally
valid or globally invalid.

This patch instead adds a way of specifying that individual operands
must be aligned.  More generally, it allows constraints to specify
a C++ condition that the operand's REGNO must satisfy.  The condition
must be invariant for a given set of target options, so that it can
be precomputed and cached as a HARD_REG_SET.

This information will be used in very compile-time-sensitive
parts of the compiler.  A lot of the complication is in allowing
the information to be stored and tested without much memory cost,
and without impacting targets that don't use the feature.

Specifically:

- Constraints are encouraged to test the absolute REGNO rather than
  an offset from the start of the containing class.  For example,
  all constraints for even registers should use the same condition,
  such as "regno % 2 == 0".  This requires the classes to start at
  even register boundaries, but that's already an implicit
  requirement due to things like the ira-costs.cc code that begins:

      /* Some targets allow pseudos to be allocated to unaligned sequences
	 of hard registers.  However, selecting an unaligned sequence can
	 unnecessarily restrict later allocations.  So increase the cost of
	 unaligned hard regs to encourage the use of aligned hard regs.  */

- Each unique condition is given a "filter identifier".

- The total number of filters is given by NUM_REGISTER_FILTERS,
  defined automatically in insn-config.h.  Structures can therefore use
  a bitfield of NUM_REGISTER_FILTERS to represent a mask of filters.

- There is a new target global, target_constraints, that caches the
  HARD_REG_SET for each filter.

- There is a function for looking up the HARD_REG_SET filter for a given
  constraint and one for looking up the filter id.  Both simply return
  a constant on targets that don't use the feature.

- There are functions for testing a register against a specific filter,
  or against a mask of filters.

This patch just adds the information.  Later ones make use of it.

gcc/
	* rtl.def (DEFINE_REGISTER_CONSTRAINT): Add an optional filter
	operand.
	* doc/md.texi (define_register_constraint): Document it.
	* doc/tm.texi.in: Reference it in discussion about aligned registers.
	* doc/tm.texi: Regenerate.
	* gensupport.h (register_filters, get_register_filter_id): Declare.
	* gensupport.cc (register_filter_map, register_filters): New variables.
	(get_register_filter_id): New function.
	(process_define_register_constraint): Likewise.
	(process_rtx): Pass define_register_constraints to
	process_define_register_constraint.
	* genconfig.cc (main): Emit a definition of NUM_REGISTER_FILTERS.
	* genpreds.cc (constraint_data): Add a filter field.
	(add_constraint): Update accordingly.
	(process_define_register_constraint): Pass the filter operand.
	(write_init_reg_class_start_regs): New function.
	(write_get_register_filter): Likewise.
	(write_get_register_filter_id): Likewise.
	(write_tm_preds_h): Write a definition of target_constraints,
	plus helpers to test its contents.  Write the get_register_filter*
	functions.
	(write_insn_preds_c): Write init_reg_class_start_regs.
	* reginfo.cc (init_reg_class_start_regs): Declare.
	(init_reg_sets): Call it.
	* target-globals.h (this_target_constraints): Declare.
	(target_globals): Add a constraints field.
	(restore_target_globals): Update accordingly.
	* target-globals.cc: Include tm_p.h.
	(default_target_globals): Initialize the constraints field.
	(save_target_globals): Handle the constraints field.
	(target_globals::~target_globals): Likewise.
---
 gcc/doc/md.texi       |  41 +++++++++++-
 gcc/doc/tm.texi       |   3 +-
 gcc/doc/tm.texi.in    |   3 +-
 gcc/genconfig.cc      |   2 +
 gcc/genpreds.cc       | 146 +++++++++++++++++++++++++++++++++++++++++-
 gcc/gensupport.cc     |  48 +++++++++++++-
 gcc/gensupport.h      |   3 +
 gcc/reginfo.cc        |   5 ++
 gcc/rtl.def           |   6 +-
 gcc/target-globals.cc |   6 +-
 gcc/target-globals.h  |   3 +
 11 files changed, 254 insertions(+), 12 deletions(-)

diff --git a/gcc/doc/md.texi b/gcc/doc/md.texi
index 5d86152e5dd..dc8c068646d 100644
--- a/gcc/doc/md.texi
+++ b/gcc/doc/md.texi
@@ -4513,8 +4513,8 @@ Register constraints correspond directly to register classes.
 @xref{Register Classes}.  There is thus not much flexibility in their
 definitions.
 
-@deffn {MD Expression} define_register_constraint name regclass docstring
-All three arguments are string constants.
+@deffn {MD Expression} define_register_constraint name regclass docstring [filter]
+All arguments are string constants.
 @var{name} is the name of the constraint, as it will appear in
 @code{match_operand} expressions.  If @var{name} is a multi-letter
 constraint its length shall be the same for all constraints starting
@@ -4526,6 +4526,43 @@ look at the operand.  The usual use of expressions is to map some
 register constraints to @code{NO_REGS} when the register class
 is not available on a given subarchitecture.
 
+If an operand occupies multiple hard registers, the constraint
+requires all of those registers to belong to @var{regclass}.
+For example, if @var{regclass} is @code{GENERAL_REGS} and
+@code{GENERAL_REGS} contains registers @code{r0} to @code{r15},
+the constraint does not allow @var{r15} to be used for modes
+that occupy more than one register.
+
+@cindex @code{TARGET_HARD_REGNO_MODE_OK} and constraints
+The choice of register is also constrained by @code{TARGET_HARD_REGNO_MODE_OK}.
+For example, if @code{TARGET_HARD_REGNO_MODE_OK} disallows @samp{(reg:DI r1)},
+that requirement applies to all constraints whose classes include @code{r1}.
+
+However, it is sometimes useful to impose extra operand-specific
+requirements on the register number.  For example, a target might not
+want to prevent @emph{all} odd-even pairs from holding @code{DImode}
+values, but it might still need to prevent specific operands from
+having an odd-numbered register.  The optional @var{filter} argument
+exists for such cases.  When given, @var{filter} is a C++ expression
+that evaluates to true if @code{regno} is a valid register for the
+operand.  If an operand occupies multiple registers, the condition
+applies only to the first register.
+
+For example:
+
+@smallexample
+(define_register_constraint "e" "GENERAL_REGS" "..." "regno % 2 == 0")
+@end smallexample
+
+defines a constraint that requires an even-numbered general register.
+
+Filter conditions that impose an alignment are encouraged to test
+the alignment of @code{regno} itself, as in the example, rather than
+calculate an offset relative to the start of the class.  If it is
+sometimes necessary for a register of class @var{c} to be aligned
+to @var{n}, the first register in @var{c} should itself by divisible
+by @var{n}.
+
 @var{docstring} is a sentence documenting the meaning of the
 constraint.  Docstrings are explained further below.
 @end deffn
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index abc23b2bb73..b13b5161161 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -2478,7 +2478,8 @@ When a value occupying several consecutive registers is expected in a
 certain class, all the registers used must belong to that class.
 Therefore, register classes cannot be used to enforce a requirement for
 a register pair to start with an even-numbered register.  The way to
-specify this requirement is with @code{TARGET_HARD_REGNO_MODE_OK}.
+specify this requirement is with @code{TARGET_HARD_REGNO_MODE_OK},
+or with a filter expression in a @code{define_register_constraint}.
 
 Register classes used for input-operands of bitwise-and or shift
 instructions have a special requirement: each such class must have, for
diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
index 3d3ae12cc2f..9a92cb97337 100644
--- a/gcc/doc/tm.texi.in
+++ b/gcc/doc/tm.texi.in
@@ -2060,7 +2060,8 @@ When a value occupying several consecutive registers is expected in a
 certain class, all the registers used must belong to that class.
 Therefore, register classes cannot be used to enforce a requirement for
 a register pair to start with an even-numbered register.  The way to
-specify this requirement is with @code{TARGET_HARD_REGNO_MODE_OK}.
+specify this requirement is with @code{TARGET_HARD_REGNO_MODE_OK},
+or with a filter expression in a @code{define_register_constraint}.
 
 Register classes used for input-operands of bitwise-and or shift
 instructions have a special requirement: each such class must have, for
diff --git a/gcc/genconfig.cc b/gcc/genconfig.cc
index 2ee323f80c3..c8c2ebef21c 100644
--- a/gcc/genconfig.cc
+++ b/gcc/genconfig.cc
@@ -360,6 +360,8 @@ main (int argc, const char **argv)
       printf ("#define MAX_INSNS_PER_PEEP2 0\n");
     }
 
+  printf ("#define NUM_REGISTER_FILTERS %d\n", register_filters.length ());
+
   puts ("\n#endif /* GCC_INSN_CONFIG_H */");
 
   if (ferror (stdout) || fflush (stdout) || fclose (stdout))
diff --git a/gcc/genpreds.cc b/gcc/genpreds.cc
index bdd65ef7d7a..5535a7512fb 100644
--- a/gcc/genpreds.cc
+++ b/gcc/genpreds.cc
@@ -677,6 +677,7 @@ public:
   size_t namelen;
   const char *regclass;  /* for register constraints */
   rtx exp;               /* for other constraints */
+  const char *filter;    /* the register filter condition, or null if none */
   unsigned int is_register	: 1;
   unsigned int is_const_int	: 1;
   unsigned int is_const_dbl	: 1;
@@ -763,7 +764,8 @@ mangle (const char *name)
    is the register class, if any; EXP is the expression to test, if any;
    IS_MEMORY, IS_SPECIAL_MEMORY, IS_RELAXED_MEMORY and IS_ADDRESS indicate
    memory, special memory, and address constraints, respectively; LOC is the .md
-   file location.
+   file location; FILTER is the filter condition for a register constraint,
+   or null if none.
 
    Not all combinations of arguments are valid; most importantly, REGCLASS is
    mutually exclusive with EXP, and
@@ -776,7 +778,8 @@ mangle (const char *name)
 static void
 add_constraint (const char *name, const char *regclass,
 		rtx exp, bool is_memory, bool is_special_memory,
-		bool is_relaxed_memory, bool is_address, file_location loc)
+		bool is_relaxed_memory, bool is_address, file_location loc,
+		const char *filter = nullptr)
 {
   class constraint_data *c, **iter, **slot;
   const char *p;
@@ -908,6 +911,7 @@ add_constraint (const char *name, const char *regclass,
   c->namelen = namelen;
   c->regclass = regclass;
   c->exp = exp;
+  c->filter = filter;
   c->is_register = regclass != 0;
   c->is_const_int = is_const_int;
   c->is_const_dbl = is_const_dbl;
@@ -966,7 +970,8 @@ static void
 process_define_register_constraint (md_rtx_info *info)
 {
   add_constraint (XSTR (info->def, 0), XSTR (info->def, 1),
-		  0, false, false, false, false, info->loc);
+		  0, false, false, false, false, info->loc,
+		  XSTR (info->def, 3));
 }
 
 /* Put the constraints into enum order.  We want to keep constraints
@@ -1319,6 +1324,34 @@ write_insn_const_int_ok_for_constraint (void)
 	"  return false;\n"
 	"}\n");
 }
+
+/* Print the init_reg_class_start_regs function, which initializes
+   this_target_constraints->register_filters from the C conditions
+   in the define_register_constraints.  */
+static void
+write_init_reg_class_start_regs ()
+{
+  printf ("\n"
+	  "void\n"
+	  "init_reg_class_start_regs ()\n"
+	  "{\n");
+  if (!register_filters.is_empty ())
+    {
+      printf ("  for (unsigned int regno = 0; regno < FIRST_PSEUDO_REGISTER;"
+	      " ++regno)\n"
+	      "    {\n");
+      for (unsigned int i = 0; i < register_filters.length (); ++i)
+	{
+	  printf ("      if (");
+	  rtx_reader_ptr->print_c_condition (register_filters[i]);
+	  printf (")\n"
+		  "        SET_HARD_REG_BIT (%s[%d], regno);\n",
+		  "this_target_constraints->register_filters", i);
+	}
+      printf ("    }\n");
+    }
+  printf ("}\n");
+}
 \f
 /* Write a definition for a function NAME that returns true if a given
    constraint_num is in the range [START, END).  */
@@ -1401,6 +1434,54 @@ print_type_tree (const vec <std::pair <unsigned int, const char *> > &vec,
   printf ("%*sreturn %s;\n", indent, "", fallback);
 }
 
+/* Print the get_register_filter function, which returns a pointer
+   to the start register filter for a given constraint, or null if none.  */
+static void
+write_get_register_filter ()
+{
+  constraint_data *c;
+
+  printf ("\n"
+	  "#ifdef GCC_HARD_REG_SET_H\n"
+	  "static inline const HARD_REG_SET *\n"
+	  "get_register_filter (constraint_num%s)\n",
+	  register_filters.is_empty () ? "" : " c");
+  printf ("{\n");
+  FOR_ALL_CONSTRAINTS (c)
+    if (c->is_register && c->filter)
+      {
+	printf ("  if (c == CONSTRAINT_%s)\n", c->c_name);
+	printf ("    return &this_target_constraints->register_filters[%d];\n",
+		get_register_filter_id (c->filter));
+      }
+  printf ("  return nullptr;\n"
+	  "}\n"
+	  "#endif\n");
+}
+
+/* Print the get_register_filter_id function, which returns the index
+   of the given constraint's register filter in
+   this_target_constraints->register_filters, or -1 if none.  */
+static void
+write_get_register_filter_id ()
+{
+  constraint_data *c;
+
+  printf ("\n"
+	  "static inline int\n"
+	  "get_register_filter_id (constraint_num%s)\n",
+	  register_filters.is_empty () ? "" : " c");
+  printf ("{\n");
+  FOR_ALL_CONSTRAINTS (c)
+    if (c->is_register && c->filter)
+      {
+	printf ("  if (c == CONSTRAINT_%s)\n", c->c_name);
+	printf ("    return %d;\n", get_register_filter_id (c->filter));
+      }
+  printf ("  return -1;\n"
+	  "}\n");
+}
+
 /* Write tm-preds.h.  Unfortunately, it is impossible to forward-declare
    an enumeration in portable C, so we have to condition all these
    prototypes on HAVE_MACHINE_MODES.  */
@@ -1425,6 +1506,53 @@ write_tm_preds_h (void)
 
   puts ("#endif /* HAVE_MACHINE_MODES */\n");
 
+  /* Print the definition of the target_constraints structure.  */
+  printf ("#ifdef GCC_HARD_REG_SET_H\n"
+	  "struct target_constraints {\n"
+	  "  HARD_REG_SET register_filters[%d];\n",
+	  MAX (register_filters.length (), 1));
+  printf ("};\n"
+	  "\n"
+	  "extern struct target_constraints default_target_constraints;\n"
+	  "#if SWITCHABLE_TARGET\n"
+	  "extern struct target_constraints *this_target_constraints;\n"
+	  "#else\n"
+	  "#define this_target_constraints (&default_target_constraints)\n"
+	  "#endif\n");
+
+  /* Print TEST_REGISTER_FILTER_BIT, which tests whether register REGNO
+     is a valid start register for register filter ID.  */
+  printf ("\n"
+	  "#define TEST_REGISTER_FILTER_BIT(ID, REGNO) \\\n");
+  if (register_filters.is_empty ())
+    printf ("  ((void) (ID), (void) (REGNO), false)\n");
+  else
+    printf ("  TEST_HARD_REG_BIT ("
+	    "this_target_constraints->register_filters[ID], REGNO)\n");
+
+  /* Print test_register_filters, which tests whether register REGNO
+     is a valid start register for the mask of register filters in MASK.  */
+  printf ("\n"
+	  "inline bool\n"
+	  "test_register_filters (unsigned int%s, unsigned int%s)\n",
+	  register_filters.is_empty () ? "" : " mask",
+	  register_filters.is_empty () ? "" : " regno");
+  printf ("{\n");
+  if (register_filters.is_empty ())
+    printf ("  return true;\n");
+  else
+    {
+      printf ("  for (unsigned int id = 0; id < %d; ++id)\n",
+	      register_filters.length ());
+      printf ("    if ((mask & (1U << id))\n"
+	      "\t&& !TEST_REGISTER_FILTER_BIT (id, regno))\n"
+	      "      return false;\n"
+	      "  return true;\n");
+    }
+  printf ("}\n"
+	  "#endif\n"
+	  "\n");
+
   if (constraint_max_namelen > 0)
     {
       write_enum_constraint_num ();
@@ -1548,6 +1676,9 @@ write_tm_preds_h (void)
 	values.safe_push (std::make_pair (address_end, "CT_FIXED_FORM"));
       print_type_tree (values, 0, values.length (), "CT_REGISTER", 2);
       puts ("}");
+
+      write_get_register_filter ();
+      write_get_register_filter_id ();
     }
 
   puts ("#endif /* tm-preds.h */");
@@ -1599,6 +1730,13 @@ write_insn_preds_c (void)
 #include \"tm-constrs.h\"\n\
 #include \"target.h\"\n");
 
+  printf ("\n"
+	  "struct target_constraints default_target_constraints;\n"
+	  "#if SWITCHABLE_TARGET\n"
+	  "struct target_constraints *this_target_constraints"
+	  " = &default_target_constraints;\n"
+	  "#endif\n");
+
   FOR_ALL_PREDICATES (p)
     write_one_predicate_function (p);
 
@@ -1613,6 +1751,8 @@ write_insn_preds_c (void)
       if (have_const_int_constraints)
 	write_insn_const_int_ok_for_constraint ();
     }
+
+  write_init_reg_class_start_regs ();
 }
 
 /* Argument parsing.  */
diff --git a/gcc/gensupport.cc b/gcc/gensupport.cc
index 688808c7d12..0ac0d0772d4 100644
--- a/gcc/gensupport.cc
+++ b/gcc/gensupport.cc
@@ -400,6 +400,45 @@ process_define_predicate (rtx desc, file_location loc)
 #undef I
 #undef N
 #undef Y
+
+/* Maps register filter conditions to the associated filter identifier.  */
+static hash_map<nofree_string_hash, unsigned int> register_filter_map;
+
+/* All register filter conditions, indexed by identifier.  */
+vec<const char *> register_filters;
+
+/* Return the unique identifier for filter condition FILTER.  Identifiers
+   are assigned automatically when the define_register_constraint is
+   parsed.  */
+
+unsigned int
+get_register_filter_id (const char *filter)
+{
+  unsigned int *slot = register_filter_map.get (filter);
+  gcc_assert (slot);
+  return *slot;
+}
+
+/* Process define_register_constraint directive DESC, at location LOC.  */
+
+static void
+process_define_register_constraint (rtx desc, file_location loc)
+{
+  /* Assign identifiers to each unique register filter condition.  */
+  if (const char *filter = XSTR (desc, 3))
+    {
+      bool existed = false;
+      unsigned int &id = register_filter_map.get_or_insert (filter, &existed);
+      if (!existed)
+	{
+	  id = register_filters.length ();
+	  if (id == 32)
+	    fatal_at (loc, "too many distinct register filters, maximum"
+		      " is 32");
+	  register_filters.safe_push (filter);
+	}
+    }
+}
 \f
 /* Queue PATTERN on LIST_TAIL.  Return the address of the new queue
    element.  */
@@ -1075,10 +1114,15 @@ process_rtx (rtx desc, file_location loc)
     case DEFINE_PREDICATE:
     case DEFINE_SPECIAL_PREDICATE:
       process_define_predicate (desc, loc);
-      /* Fall through.  */
+      queue_pattern (desc, &define_pred_tail, loc);
+      break;
 
-    case DEFINE_CONSTRAINT:
     case DEFINE_REGISTER_CONSTRAINT:
+      process_define_register_constraint (desc, loc);
+      queue_pattern (desc, &define_pred_tail, loc);
+      break;
+
+    case DEFINE_CONSTRAINT:
     case DEFINE_MEMORY_CONSTRAINT:
     case DEFINE_SPECIAL_MEMORY_CONSTRAINT:
     case DEFINE_RELAXED_MEMORY_CONSTRAINT:
diff --git a/gcc/gensupport.h b/gcc/gensupport.h
index 7396118714b..27e8444a745 100644
--- a/gcc/gensupport.h
+++ b/gcc/gensupport.h
@@ -108,6 +108,9 @@ struct optab_def
 extern optab_def optabs[];
 extern unsigned int num_optabs;
 
+extern vec<const char *> register_filters;
+extern unsigned int get_register_filter_id (const char *);
+
 /* Information about an instruction name that matches an optab pattern.  */
 struct optab_pattern
 {
diff --git a/gcc/reginfo.cc b/gcc/reginfo.cc
index d472a35946a..5b6e706b35d 100644
--- a/gcc/reginfo.cc
+++ b/gcc/reginfo.cc
@@ -140,6 +140,9 @@ reginfo_cc_finalize (void)
   CLEAR_HARD_REG_SET (global_reg_set);
 }
 
+/* In insn-preds.cc.  */
+extern void init_reg_class_start_regs ();
+
 /* Given a register bitmap, turn on the bits in a HARD_REG_SET that
    correspond to the hard registers, if any, set in that map.  This
    could be done far more efficiently by having all sorts of special-cases
@@ -198,6 +201,8 @@ init_reg_sets (void)
 
   SET_HARD_REG_SET (accessible_reg_set);
   SET_HARD_REG_SET (operand_reg_set);
+
+  init_reg_class_start_regs ();
 }
 
 /* We need to save copies of some of the register information which
diff --git a/gcc/rtl.def b/gcc/rtl.def
index 88e2b198503..a40e1a7bb18 100644
--- a/gcc/rtl.def
+++ b/gcc/rtl.def
@@ -1016,8 +1016,10 @@ DEF_RTL_EXPR(DEFINE_SPECIAL_PREDICATE, "define_special_predicate", "ses", RTX_EX
       at -m switches and the like.
    2: A docstring for this constraint, in Texinfo syntax; not currently
       used, in future will be incorporated into the manual's list of
-      machine-specific operand constraints.  */
-DEF_RTL_EXPR(DEFINE_REGISTER_CONSTRAINT, "define_register_constraint", "sss", RTX_EXTRA)
+      machine-specific operand constraints.
+   3: A C expression that evalutes to true if "regno" is a valid
+      start register.  */
+DEF_RTL_EXPR(DEFINE_REGISTER_CONSTRAINT, "define_register_constraint", "sssS", RTX_EXTRA)
 
 /* Definition of a non-register operand constraint.  These look at the
    operand and decide whether it fits the constraint.
diff --git a/gcc/target-globals.cc b/gcc/target-globals.cc
index 81244b127fc..cfa0045e02c 100644
--- a/gcc/target-globals.cc
+++ b/gcc/target-globals.cc
@@ -41,6 +41,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "bb-reorder.h"
 #include "lower-subreg.h"
 #include "function-abi.h"
+#include "tm_p.h"
 
 #if SWITCHABLE_TARGET
 class target_globals default_target_globals = {
@@ -60,7 +61,8 @@ class target_globals default_target_globals = {
   &default_target_builtins,
   &default_target_gcse,
   &default_target_bb_reorder,
-  &default_target_lower_subreg
+  &default_target_lower_subreg,
+  &default_target_constraints
 };
 
 class target_globals *
@@ -84,6 +86,7 @@ save_target_globals (void)
   g->gcse = XCNEW (struct target_gcse);
   g->bb_reorder = XCNEW (struct target_bb_reorder);
   g->lower_subreg = XCNEW (struct target_lower_subreg);
+  g->constraints = XCNEW (target_constraints);
   restore_target_globals (g);
   init_reg_sets ();
   target_reinit ();
@@ -141,6 +144,7 @@ target_globals::~target_globals ()
       XDELETE (gcse);
       XDELETE (bb_reorder);
       XDELETE (lower_subreg);
+      XDELETE (constraints);
     }
 }
 
diff --git a/gcc/target-globals.h b/gcc/target-globals.h
index daedf66017f..42f082c589c 100644
--- a/gcc/target-globals.h
+++ b/gcc/target-globals.h
@@ -38,6 +38,7 @@ extern struct target_builtins *this_target_builtins;
 extern struct target_gcse *this_target_gcse;
 extern struct target_bb_reorder *this_target_bb_reorder;
 extern struct target_lower_subreg *this_target_lower_subreg;
+extern struct target_constraints *this_target_constraints;
 #endif
 
 class GTY(()) target_globals {
@@ -61,6 +62,7 @@ public:
   struct target_gcse *GTY((skip)) gcse;
   struct target_bb_reorder *GTY((skip)) bb_reorder;
   struct target_lower_subreg *GTY((skip)) lower_subreg;
+  struct target_constraints *GTY((skip)) constraints;
 };
 
 #if SWITCHABLE_TARGET
@@ -89,6 +91,7 @@ restore_target_globals (class target_globals *g)
   this_target_gcse = g->gcse;
   this_target_bb_reorder = g->bb_reorder;
   this_target_lower_subreg = g->lower_subreg;
+  this_target_constraints = g->constraints;
 }
 #endif
 
-- 
2.25.1

[PATCH 2/5] recog: Handle register filters

[Richard Sandiford]

The main (but simplest) part of this patch makes constrain_operands
take register filters into account.

The rest of the patch adds register filter information to
operand_alternative.  Generally, if two register constraints
have different register filters, it's better if they're in separate
alternatives.  However, the syntax doesn't enforce that, and we can't
assert it due to inline asms.  So it's a choice between (a) adding
code to enforce consistent filters or (b) dealing with mixes of filters
in a conservatively correct way (in the sense of not allowing invalid
operands).  The latter seems much easier.

The patch therefore adds a mask of the filters that apply
to at least one constraint in a given operand alternative.
A register is OK if it passes all of the filters in the mask.

gcc/
	* recog.h (operand_alternative): Add a register_filters field.
	(alternative_register_filters): New function.
	* recog.cc (preprocess_constraints): Calculate the filters field.
	(constrain_operands): Check register filters.
---
 gcc/recog.cc | 14 ++++++++++++--
 gcc/recog.h  | 24 ++++++++++++++++++++++--
 2 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/gcc/recog.cc b/gcc/recog.cc
index 3bd2d73c259..eaab79c25d7 100644
--- a/gcc/recog.cc
+++ b/gcc/recog.cc
@@ -2857,6 +2857,7 @@ preprocess_constraints (int n_operands, int n_alternatives,
       for (j = 0; j < n_alternatives; j++, op_alt += n_operands)
 	{
 	  op_alt[i].cl = NO_REGS;
+	  op_alt[i].register_filters = 0;
 	  op_alt[i].constraint = p;
 	  op_alt[i].matches = -1;
 	  op_alt[i].matched = -1;
@@ -2919,7 +2920,12 @@ preprocess_constraints (int n_operands, int n_alternatives,
 		    case CT_REGISTER:
 		      cl = reg_class_for_constraint (cn);
 		      if (cl != NO_REGS)
-			op_alt[i].cl = reg_class_subunion[op_alt[i].cl][cl];
+			{
+			  op_alt[i].cl = reg_class_subunion[op_alt[i].cl][cl];
+			  auto filter_id = get_register_filter_id (cn);
+			  if (filter_id >= 0)
+			    op_alt[i].register_filters |= 1U << filter_id;
+			}
 		      break;
 
 		    case CT_CONST_INT:
@@ -3219,13 +3225,17 @@ constrain_operands (int strict, alternative_mask alternatives)
 		  enum reg_class cl = reg_class_for_constraint (cn);
 		  if (cl != NO_REGS)
 		    {
+		      auto *filter = get_register_filter (cn);
 		      if (strict < 0
 			  || (strict == 0
 			      && REG_P (op)
 			      && REGNO (op) >= FIRST_PSEUDO_REGISTER)
 			  || (strict == 0 && GET_CODE (op) == SCRATCH)
 			  || (REG_P (op)
-			      && reg_fits_class_p (op, cl, offset, mode)))
+			      && reg_fits_class_p (op, cl, offset, mode)
+			      && (!filter
+				  || TEST_HARD_REG_BIT (*filter,
+							REGNO (op) + offset))))
 			win = true;
 		    }
 
diff --git a/gcc/recog.h b/gcc/recog.h
index c6ef619c5dd..5c801e7bb81 100644
--- a/gcc/recog.h
+++ b/gcc/recog.h
@@ -42,6 +42,7 @@ enum op_type {
   OP_INOUT
 };
 
+#ifndef GENERATOR_FILE
 struct operand_alternative
 {
   /* Pointer to the beginning of the constraint string for this alternative,
@@ -62,6 +63,11 @@ struct operand_alternative
      matches this one.  */
   int matched : 8;
 
+  /* Bit ID is set if the constraint string includes a register constraint with
+     register filter ID.  Use test_register_filters (REGISTER_FILTERS, REGNO)
+     to test whether REGNO is a valid start register for the operand.  */
+  unsigned int register_filters : MAX (NUM_REGISTER_FILTERS, 1);
+
   /* Nonzero if '&' was found in the constraint string.  */
   unsigned int earlyclobber : 1;
   /* Nonzero if TARGET_MEM_CONSTRAINT was found in the constraint
@@ -72,8 +78,6 @@ struct operand_alternative
   /* Nonzero if 'X' was found in the constraint string, or if the constraint
      string for this alternative was empty.  */
   unsigned int anything_ok : 1;
-
-  unsigned int unused : 12;
 };
 
 /* Return the class for operand I of alternative ALT, taking matching
@@ -85,6 +89,18 @@ alternative_class (const operand_alternative *alt, int i)
   return alt[i].matches >= 0 ? alt[alt[i].matches].cl : alt[i].cl;
 }
 
+/* Return the mask of register filters that should be applied to operand I
+   of alternative ALT, taking matching constraints into account.  */
+
+inline unsigned int
+alternative_register_filters (const operand_alternative *alt, int i)
+{
+  return (alt[i].matches >= 0
+	  ? alt[alt[i].matches].register_filters
+	  : alt[i].register_filters);
+}
+#endif
+
 /* A class for substituting one rtx for another within an instruction,
    or for recursively simplifying the instruction as-is.  Derived classes
    can record or filter certain decisions.  */
@@ -242,9 +258,11 @@ extern void extract_insn (rtx_insn *);
 extern void extract_constrain_insn (rtx_insn *insn);
 extern void extract_constrain_insn_cached (rtx_insn *);
 extern void extract_insn_cached (rtx_insn *);
+#ifndef GENERATOR_FILE
 extern void preprocess_constraints (int, int, const char **,
 				    operand_alternative *, rtx **);
 extern const operand_alternative *preprocess_insn_constraints (unsigned int);
+#endif
 extern void preprocess_constraints (rtx_insn *);
 extern rtx_insn *peep2_next_insn (int);
 extern bool peep2_regno_dead_p (int, int);
@@ -380,6 +398,7 @@ struct recog_data_d
 
 extern struct recog_data_d recog_data;
 
+#ifndef GENERATOR_FILE
 extern const operand_alternative *recog_op_alt;
 
 /* Return a pointer to an array in which index OP describes the constraints
@@ -393,6 +412,7 @@ which_op_alt ()
 				 recog_data.n_alternatives - 1));
   return &recog_op_alt[which_alternative * recog_data.n_operands];
 }
+#endif
 
 /* A table defined in insn-output.cc that give information about
    each insn-code value.  */
-- 
2.25.1

[PATCH 3/5] lra: Handle register filters

[Richard Sandiford]

This patch makes LRA apply register filters.  This plus the recog
change is enough for correct code generation, but a follow-on IRA
patch improves the allocation.

All the new code should be optimised away on targets that don't
use register filters.  That's because get_register_filter just
wraps "return nullptr" on those targets.

gcc/
	* lra-constraints.cc (process_alt_operands): Check register filters.
---
 gcc/lra-constraints.cc | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/gcc/lra-constraints.cc b/gcc/lra-constraints.cc
index 0607c8be7cb..9b6a2af5b75 100644
--- a/gcc/lra-constraints.cc
+++ b/gcc/lra-constraints.cc
@@ -2149,6 +2149,7 @@ process_alt_operands (int only_alternative)
   int reload_nregs, reload_sum;
   bool costly_p;
   enum reg_class cl;
+  const HARD_REG_SET *cl_filter;
 
   /* Calculate some data common for all alternatives to speed up the
      function.	*/
@@ -2514,6 +2515,7 @@ process_alt_operands (int only_alternative)
 		      || spilled_pseudo_p (op))
 		    win = true;
 		  cl = GENERAL_REGS;
+		  cl_filter = nullptr;
 		  goto reg;
 
 		default:
@@ -2523,7 +2525,10 @@ process_alt_operands (int only_alternative)
 		    case CT_REGISTER:
 		      cl = reg_class_for_constraint (cn);
 		      if (cl != NO_REGS)
-			goto reg;
+			{
+			  cl_filter = get_register_filter (cn);
+			  goto reg;
+			}
 		      break;
 
 		    case CT_CONST_INT:
@@ -2567,6 +2572,7 @@ process_alt_operands (int only_alternative)
 			win = true;
 		      cl = base_reg_class (VOIDmode, ADDR_SPACE_GENERIC,
 					   ADDRESS, SCRATCH);
+		      cl_filter = nullptr;
 		      badop = false;
 		      goto reg;
 
@@ -2600,6 +2606,8 @@ process_alt_operands (int only_alternative)
 		    this_alternative_exclude_start_hard_regs
 		      |= ira_exclude_class_mode_regs[cl][mode];
 		  this_alternative_set |= reg_class_contents[cl];
+		  if (cl_filter)
+		    this_alternative_exclude_start_hard_regs |= ~*cl_filter;
 		  if (costly_p)
 		    {
 		      this_costly_alternative
@@ -2613,6 +2621,9 @@ process_alt_operands (int only_alternative)
 		      if (hard_regno[nop] >= 0
 			  && in_hard_reg_set_p (this_alternative_set,
 						mode, hard_regno[nop])
+			  && (!cl_filter
+			      || TEST_HARD_REG_BIT (*cl_filter,
+						    hard_regno[nop]))
 			  && ((REG_ATTRS (op) && (decl = REG_EXPR (op)) != NULL
 			       && VAR_P (decl) && DECL_HARD_REGISTER (decl))
 			      || !(TEST_HARD_REG_BIT
-- 
2.25.1

[PATCH 4/5] ira: Handle register filters

[Richard Sandiford]

This patch makes IRA apply register filters when picking hard registers.
All the new code should be optimised away on targets that don't use
register filters.  On targets that do use them, the new register_filters
bitfield is expected to be only a handful of bits.

Information about register filters is recorded in process_bb_node_lives.
The information isn't really related to liveness, but it's a convenient
point because (a) we've already built the allocno structures and
(b) we've already extracted the insn and preprocessed the constraints.

gcc/
	* ira-int.h (ira_allocno): Add a register_filters field.
	(ALLOCNO_REGISTER_FILTERS): New macro.
	(ALLOCNO_SET_REGISTER_FILTERS): Likewise.
	* ira-build.cc (ira_create_allocno): Initialize register_filters.
	(create_cap_allocno): Propagate register_filters.
	(propagate_allocno_info): Likewise.
	(propagate_some_info_from_allocno): Likewise.
	* ira-lives.cc (process_register_constraint_filters): New function.
	(process_bb_node_lives): Use it to record register filter
	information.
	* ira-color.cc (assign_hard_reg): Check register filters.
	(improve_allocation, fast_allocation): Likewise.
---
 gcc/ira-build.cc |  8 +++++++
 gcc/ira-color.cc | 10 ++++++++
 gcc/ira-int.h    | 14 +++++++++++
 gcc/ira-lives.cc | 61 ++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 93 insertions(+)

diff --git a/gcc/ira-build.cc b/gcc/ira-build.cc
index 93e46033170..c715a834f12 100644
--- a/gcc/ira-build.cc
+++ b/gcc/ira-build.cc
@@ -498,6 +498,7 @@ ira_create_allocno (int regno, bool cap_p,
   ALLOCNO_NREFS (a) = 0;
   ALLOCNO_FREQ (a) = 0;
   ALLOCNO_MIGHT_CONFLICT_WITH_PARENT_P (a) = false;
+  ALLOCNO_SET_REGISTER_FILTERS (a, 0);
   ALLOCNO_HARD_REGNO (a) = -1;
   ALLOCNO_CALL_FREQ (a) = 0;
   ALLOCNO_CALLS_CROSSED_NUM (a) = 0;
@@ -902,6 +903,7 @@ create_cap_allocno (ira_allocno_t a)
   ALLOCNO_NREFS (cap) = ALLOCNO_NREFS (a);
   ALLOCNO_FREQ (cap) = ALLOCNO_FREQ (a);
   ALLOCNO_CALL_FREQ (cap) = ALLOCNO_CALL_FREQ (a);
+  ALLOCNO_SET_REGISTER_FILTERS (cap, ALLOCNO_REGISTER_FILTERS (a));
 
   merge_hard_reg_conflicts (a, cap, false);
 
@@ -2064,6 +2066,9 @@ propagate_allocno_info (void)
 	    ALLOCNO_BAD_SPILL_P (parent_a) = false;
 	  ALLOCNO_NREFS (parent_a) += ALLOCNO_NREFS (a);
 	  ALLOCNO_FREQ (parent_a) += ALLOCNO_FREQ (a);
+	  ALLOCNO_SET_REGISTER_FILTERS (parent_a,
+					ALLOCNO_REGISTER_FILTERS (parent_a)
+					| ALLOCNO_REGISTER_FILTERS (a));
 
 	  /* If A's allocation can differ from PARENT_A's, we can if necessary
 	     spill PARENT_A on entry to A's loop and restore it afterwards.
@@ -2465,6 +2470,9 @@ propagate_some_info_from_allocno (ira_allocno_t a, ira_allocno_t from_a)
   ALLOCNO_CROSSED_CALLS_ABIS (a) |= ALLOCNO_CROSSED_CALLS_ABIS (from_a);
   ALLOCNO_CROSSED_CALLS_CLOBBERED_REGS (a)
     |= ALLOCNO_CROSSED_CALLS_CLOBBERED_REGS (from_a);
+  ALLOCNO_SET_REGISTER_FILTERS (a,
+				ALLOCNO_REGISTER_FILTERS (from_a)
+				| ALLOCNO_REGISTER_FILTERS (a));
 
   ALLOCNO_EXCESS_PRESSURE_POINTS_NUM (a)
     += ALLOCNO_EXCESS_PRESSURE_POINTS_NUM (from_a);
diff --git a/gcc/ira-color.cc b/gcc/ira-color.cc
index f2e8ea34152..214a4f16d3c 100644
--- a/gcc/ira-color.cc
+++ b/gcc/ira-color.cc
@@ -2163,6 +2163,9 @@ assign_hard_reg (ira_allocno_t a, bool retry_p)
       if (! check_hard_reg_p (a, hard_regno,
 			      conflicting_regs, profitable_hard_regs))
 	continue;
+      if (NUM_REGISTER_FILTERS
+	  && !test_register_filters (ALLOCNO_REGISTER_FILTERS (a), hard_regno))
+	continue;
       cost = costs[i];
       full_cost = full_costs[i];
       if (!HONOR_REG_ALLOC_ORDER)
@@ -3205,6 +3208,9 @@ improve_allocation (void)
 	  if (! check_hard_reg_p (a, hregno,
 				  conflicting_regs, profitable_hard_regs))
 	    continue;
+	  if (NUM_REGISTER_FILTERS
+	      && !test_register_filters (ALLOCNO_REGISTER_FILTERS (a), hregno))
+	    continue;
 	  ira_assert (ira_class_hard_reg_index[aclass][hregno] == j);
 	  k = allocno_costs == NULL ? 0 : j;
 	  costs[hregno] = (allocno_costs == NULL
@@ -5275,6 +5281,10 @@ fast_allocation (void)
 	      || (TEST_HARD_REG_BIT
 		  (ira_prohibited_class_mode_regs[aclass][mode], hard_regno)))
 	    continue;
+	  if (NUM_REGISTER_FILTERS
+	      && !test_register_filters (ALLOCNO_REGISTER_FILTERS (a),
+					 hard_regno))
+	    continue;
 	  if (costs == NULL)
 	    {
 	      best_hard_regno = hard_regno;
diff --git a/gcc/ira-int.h b/gcc/ira-int.h
index 0685e1f4e8d..1c3548df4ea 100644
--- a/gcc/ira-int.h
+++ b/gcc/ira-int.h
@@ -328,6 +328,13 @@ struct ira_allocno
 
      This is only ever true for non-cap allocnos.  */
   unsigned int might_conflict_with_parent_p : 1;
+#ifndef NUM_REGISTER_FILTERS
+#error "insn-config.h not included"
+#elif NUM_REGISTER_FILTERS
+  /* The set of register filters applied to the allocno by operand
+     alternatives that accept class ACLASS.  */
+  unsigned int register_filters : NUM_REGISTER_FILTERS;
+#endif
   /* Accumulated usage references of the allocno.  Here and below,
      word 'accumulated' means info for given region and all nested
      subregions.  In this case, 'accumulated' means sum of references
@@ -432,6 +439,13 @@ struct ira_allocno
 #define ALLOCNO_FREQ(A) ((A)->freq)
 #define ALLOCNO_MIGHT_CONFLICT_WITH_PARENT_P(A) \
   ((A)->might_conflict_with_parent_p)
+#if NUM_REGISTER_FILTERS
+#define ALLOCNO_REGISTER_FILTERS(A) (A)->register_filters
+#define ALLOCNO_SET_REGISTER_FILTERS(A, X) ((A)->register_filters = (X))
+#else
+#define ALLOCNO_REGISTER_FILTERS(A) 0
+#define ALLOCNO_SET_REGISTER_FILTERS(A, X) ((void) (A), gcc_assert ((X) == 0))
+#endif
 #define ALLOCNO_HARD_REGNO(A) ((A)->hard_regno)
 #define ALLOCNO_CALL_FREQ(A) ((A)->call_freq)
 #define ALLOCNO_CALLS_CROSSED_NUM(A) ((A)->calls_crossed_num)
diff --git a/gcc/ira-lives.cc b/gcc/ira-lives.cc
index 81af5c06460..63f2314409f 100644
--- a/gcc/ira-lives.cc
+++ b/gcc/ira-lives.cc
@@ -1066,6 +1066,66 @@ process_single_reg_class_operands (bool in_p, int freq)
     }
 }
 
+/* Go through the operands of the extracted insn looking for operand
+   alternatives that apply a register filter.  Record any such filters
+   in the operand's allocno.  */
+static void
+process_register_constraint_filters ()
+{
+  for (int opno = 0; opno < recog_data.n_operands; ++opno)
+    {
+      rtx op = recog_data.operand[opno];
+      if (SUBREG_P (op))
+	op = SUBREG_REG (op);
+      if (REG_P (op) && !HARD_REGISTER_P (op))
+	{
+	  ira_allocno_t a = ira_curr_regno_allocno_map[REGNO (op)];
+	  for (int alt = 0; alt < recog_data.n_alternatives; alt++)
+	    {
+	      if (!TEST_BIT (preferred_alternatives, alt))
+		continue;
+
+	      auto *op_alt = &recog_op_alt[alt * recog_data.n_operands];
+	      auto cl = alternative_class (op_alt, opno);
+	      /* The two extremes are easy:
+
+		 - We should record the filter if CL matches the
+		   allocno class.
+
+		 - We should ignore the filter if CL and the allocno class
+		   are disjoint.  We'll either pick a different alternative
+		   or reload the operand.
+
+		 Things are trickier if the classes overlap.  However:
+
+		 - If the allocno class includes registers that are not
+		   in CL, some choices of hard register will need a reload
+		   anyway.  It isn't obvious that reloads due to filters
+		   are worse than reloads due to regnos being outside CL.
+
+		 - Conversely, if the allocno class is a subset of CL,
+		   any allocation will satisfy the class requirement.
+		   We should try to make sure it satisfies the filter
+		   requirement too.  This is useful if, for example,
+		   an allocno needs to be in "low" registers to satisfy
+		   some uses, and its allocno class is therefore those
+		   low registers, but the allocno is elsewhere allowed
+		   to be in any even-numbered register.  Picking an
+		   even-numbered low register satisfies both types of use.  */
+	      if (!ira_class_subset_p[ALLOCNO_CLASS (a)][cl])
+		continue;
+
+	      auto filters = alternative_register_filters (op_alt, opno);
+	      if (!filters)
+		continue;
+
+	      filters |= ALLOCNO_REGISTER_FILTERS (a);
+	      ALLOCNO_SET_REGISTER_FILTERS (a, filters);
+	    }
+	}
+    }
+}
+
 /* Look through the CALL_INSN_FUNCTION_USAGE of a call insn INSN, and see if
    we find a SET rtx that we can use to deduce that a register can be cheaply
    caller-saved.  Return such a register, or NULL_RTX if none is found.  */
@@ -1378,6 +1438,7 @@ process_bb_node_lives (ira_loop_tree_node_t loop_tree_node)
 	      }
 
 	  preferred_alternatives = ira_setup_alts (insn);
+	  process_register_constraint_filters ();
 	  process_single_reg_class_operands (false, freq);
 
 	  if (call_p)
-- 
2.25.1

[PATCH 5/5] Add an aligned_register_operand predicate

[Richard Sandiford]

This patch adds a target-independent aligned_register_operand
predicate, for use with register constraints that use filters
to impose an alignment.  The definition deliberately jetisons
some of the historical baggage in general_operand.

gcc/
	* common.md (aligned_register_operand): New predicate.
---
 gcc/common.md | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/gcc/common.md b/gcc/common.md
index 51ecd79786b..91a72bd7731 100644
--- a/gcc/common.md
+++ b/gcc/common.md
@@ -17,6 +17,34 @@
 ;; along with GCC; see the file COPYING3.  If not see
 ;; <http://www.gnu.org/licenses/>.  */
 
+;; This predicate is intended to be paired with register constraints that use
+;; register filters to impose an alignment.  Operands that are aligned via
+;; TARGET_HARD_REGNO_MODE_OK should use normal register_operands instead.
+(define_predicate "aligned_register_operand"
+  (match_code "reg,subreg")
+{
+  /* Require the offset in a non-paradoxical subreg to be naturally aligned.
+     For example, if we have a subreg of something that is double the size of
+     this operand, the offset must select the first or second half of it.  */
+  if (SUBREG_P (op)
+      && multiple_p (SUBREG_BYTE (op), GET_MODE_SIZE (GET_MODE (op))))
+    op = SUBREG_REG (op);
+  if (!REG_P (op))
+    return false;
+
+  if (HARD_REGISTER_P (op))
+    {
+      if (!in_hard_reg_set_p (operand_reg_set, GET_MODE (op), REGNO (op)))
+	return false;
+
+      /* Reject hard registers that would need reloading, so that the reload
+	 is visible to IRA and to pre-RA optimizers.  */
+      if (REGNO (op) % REG_NREGS (op) != 0)
+	return false;
+    }
+  return true;
+})
+
 (define_register_constraint "r" "GENERAL_REGS"
   "Matches any general register.")
 
-- 
2.25.1

Re: [PATCH 0/5] Add support for operand-specific alignment requirements

[Vladimir Makarov]

On 11/12/23 09:52, Richard Sandiford wrote:
> SME has various instructions that require aligned register tuples.
> However, the associated tuple modes are already widely used and do
> not need to be aligned in other contexts.  It therefore isn't
> appropriate to force alignment in TARGET_HARD_REGNO_MODE_OK.
>
> There are also strided loads and stores that require:
>
> - (regno & 0x8) == 0 for 2-register tuples
> - (regno & 0xc) == 0 for 4-register tuples
>
> Although the requirements for strided loads and stores could be
> enforced by C++ conditions on the insn, it's convenient to handle
> them in the same way as alignment.
>
> This series of patches therefore adds a way for register constraints
> to specify which start registers are valid and which aren't.  Most of
> the details are in the covering note to the first patch.
>
> This is clearly changing a performance-sensitive part of the compiler.
> I've tried to ensure that the overhead is only small for targets that
> use the new feature.  Almost all of the new code gets optimised away
> on targets that don't use the feature.
>
> Richard Sandiford (5):
>    Add register filter operand to define_register_constraint
>    recog: Handle register filters
>    lra: Handle register filters
>    ira: Handle register filters
>    Add an aligned_register_operand predicate
>
>   gcc/common.md          |  28 ++++++++
>   gcc/doc/md.texi        |  41 +++++++++++-
>   gcc/doc/tm.texi        |   3 +-
>   gcc/doc/tm.texi.in     |   3 +-
>   gcc/genconfig.cc       |   2 +
>   gcc/genpreds.cc        | 146 ++++++++++++++++++++++++++++++++++++++++-
>   gcc/gensupport.cc      |  48 +++++++++++++-
>   gcc/gensupport.h       |   3 +
>   gcc/ira-build.cc       |   8 +++
>   gcc/ira-color.cc       |  10 +++
>   gcc/ira-int.h          |  14 ++++
>   gcc/ira-lives.cc       |  61 +++++++++++++++++
>   gcc/lra-constraints.cc |  13 +++-
>   gcc/recog.cc           |  14 +++-
>   gcc/recog.h            |  24 ++++++-
>   gcc/reginfo.cc         |   5 ++
>   gcc/rtl.def            |   6 +-
>   gcc/target-globals.cc  |   6 +-
>   gcc/target-globals.h   |   3 +
>   19 files changed, 421 insertions(+), 17 deletions(-)
>
Collecting all occurrence constraints for IRA probably might result in 
worse allocation (when pseudo is spilled because of this) in comparison 
with using wider hard reg set and generating reload insns for some 
pseudo occurrences requiring stricter constraints.  Regional RA 
mitigates this issue.  In any case IRA changes is an improvement in 
comparison with using only hard_regno_mode_ok.  Using smaller 
constraints in certain cases for pseudos spilled after using the biggest 
constraint is just an idea for further RA improvement for targets using 
the filters. The only question is it worth to implement.

All IRA/LRA/reginfo patches are OK for me.  IMHO other changes are 
pretty strait forward not to ask somebody to review them.

Thank you, Richard.

Re: [PATCH 1/5] Add register filter operand to define_register_constraint

[Jeff Law]

On 11/12/23 07:52, Richard Sandiford wrote:
> The main way of enforcing registers to be aligned is through
> HARD_REGNO_MODE_OK.  But this is a global property that applies
> to all operands.  A given (regno, mode) pair is either globally
> valid or globally invalid.
> 
> This patch instead adds a way of specifying that individual operands
> must be aligned.  More generally, it allows constraints to specify
> a C++ condition that the operand's REGNO must satisfy.  The condition
> must be invariant for a given set of target options, so that it can
> be precomputed and cached as a HARD_REG_SET.
> 
> This information will be used in very compile-time-sensitive
> parts of the compiler.  A lot of the complication is in allowing
> the information to be stored and tested without much memory cost,
> and without impacting targets that don't use the feature.
> 
> Specifically:
> 
> - Constraints are encouraged to test the absolute REGNO rather than
>    an offset from the start of the containing class.  For example,
>    all constraints for even registers should use the same condition,
>    such as "regno % 2 == 0".  This requires the classes to start at
>    even register boundaries, but that's already an implicit
>    requirement due to things like the ira-costs.cc code that begins:
> 
>        /* Some targets allow pseudos to be allocated to unaligned sequences
> 	 of hard registers.  However, selecting an unaligned sequence can
> 	 unnecessarily restrict later allocations.  So increase the cost of
> 	 unaligned hard regs to encourage the use of aligned hard regs.  */
> 
> - Each unique condition is given a "filter identifier".
> 
> - The total number of filters is given by NUM_REGISTER_FILTERS,
>    defined automatically in insn-config.h.  Structures can therefore use
>    a bitfield of NUM_REGISTER_FILTERS to represent a mask of filters.
> 
> - There is a new target global, target_constraints, that caches the
>    HARD_REG_SET for each filter.
> 
> - There is a function for looking up the HARD_REG_SET filter for a given
>    constraint and one for looking up the filter id.  Both simply return
>    a constant on targets that don't use the feature.
> 
> - There are functions for testing a register against a specific filter,
>    or against a mask of filters.
> 
> This patch just adds the information.  Later ones make use of it.
> 
> gcc/
> 	* rtl.def (DEFINE_REGISTER_CONSTRAINT): Add an optional filter
> 	operand.
> 	* doc/md.texi (define_register_constraint): Document it.
> 	* doc/tm.texi.in: Reference it in discussion about aligned registers.
> 	* doc/tm.texi: Regenerate.
> 	* gensupport.h (register_filters, get_register_filter_id): Declare.
> 	* gensupport.cc (register_filter_map, register_filters): New variables.
> 	(get_register_filter_id): New function.
> 	(process_define_register_constraint): Likewise.
> 	(process_rtx): Pass define_register_constraints to
> 	process_define_register_constraint.
> 	* genconfig.cc (main): Emit a definition of NUM_REGISTER_FILTERS.
> 	* genpreds.cc (constraint_data): Add a filter field.
> 	(add_constraint): Update accordingly.
> 	(process_define_register_constraint): Pass the filter operand.
> 	(write_init_reg_class_start_regs): New function.
> 	(write_get_register_filter): Likewise.
> 	(write_get_register_filter_id): Likewise.
> 	(write_tm_preds_h): Write a definition of target_constraints,
> 	plus helpers to test its contents.  Write the get_register_filter*
> 	functions.
> 	(write_insn_preds_c): Write init_reg_class_start_regs.
> 	* reginfo.cc (init_reg_class_start_regs): Declare.
> 	(init_reg_sets): Call it.
> 	* target-globals.h (this_target_constraints): Declare.
> 	(target_globals): Add a constraints field.
> 	(restore_target_globals): Update accordingly.
> 	* target-globals.cc: Include tm_p.h.
> 	(default_target_globals): Initialize the constraints field.
> 	(save_target_globals): Handle the constraints field.
> 	(target_globals::~target_globals): Likewise.
OK.  Mostly focused on the concept -- if we need to iterate on the 
implementation after your using it we can certainly do that.

Jeff

Re: [PATCH 2/5] recog: Handle register filters

[Jeff Law]

On 11/12/23 07:52, Richard Sandiford wrote:
> The main (but simplest) part of this patch makes constrain_operands
> take register filters into account.
> 
> The rest of the patch adds register filter information to
> operand_alternative.  Generally, if two register constraints
> have different register filters, it's better if they're in separate
> alternatives.  However, the syntax doesn't enforce that, and we can't
> assert it due to inline asms.  So it's a choice between (a) adding
> code to enforce consistent filters or (b) dealing with mixes of filters
> in a conservatively correct way (in the sense of not allowing invalid
> operands).  The latter seems much easier.
> 
> The patch therefore adds a mask of the filters that apply
> to at least one constraint in a given operand alternative.
> A register is OK if it passes all of the filters in the mask.
> 
> gcc/
> 	* recog.h (operand_alternative): Add a register_filters field.
> 	(alternative_register_filters): New function.
> 	* recog.cc (preprocess_constraints): Calculate the filters field.
> 	(constrain_operands): Check register filters.
OK
jeff

Re: [PATCH 5/5] Add an aligned_register_operand predicate

[Jeff Law]

On 11/12/23 07:52, Richard Sandiford wrote:
> This patch adds a target-independent aligned_register_operand
> predicate, for use with register constraints that use filters
> to impose an alignment.  The definition deliberately jetisons
> some of the historical baggage in general_operand.
> 
> gcc/
> 	* common.md (aligned_register_operand): New predicate.
OK
jeff