Re: Remove mode argument from gen_rtx_SET

[Richard Sandiford <richard.sandiford@arm.com>]

Jeff Law <law@redhat.com> writes:
> On 05/07/2015 05:37 AM, Richard Sandiford wrote:
>> One problem with the automatically-generated gen_rtx_FOO () macros
>> is that they always have a mode parameter, even for codes like SET
>> where the mode should always be VOIDmode.  This inevitably leads to
>> cases where a caller accidentally passes something other than VOIDmode.
>> E.g. when expanding an SImode move, the temptation is to make everything
>> SImode, even the SETs.  This in turn can cause two instructions to appear
>> different simply because their SETs have different modes, even though the
>> SET_DEST and SET_SRC are identical.
>>
>> E.g. for gcc/testsuite/g++.dg/torture/pr34651.C on lm32-elf we have
>> the following before jump2:
>>
>>    (jump_insn 42 191 43 5 (set (pc)
>> 	  (if_then_else (eq:SI (reg:SI 13 r13 [orig:43 inHotKey$4+-3 ] [43])
>> 		  (const_int 0 [0]))
>> 	      (label_ref 53)
>> 	      (pc))) gcc/testsuite/g++.dg/torture/pr34651.C:22 22 {*beq}
>>         (expr_list:REG_DEAD (reg:SI 13 r13 [orig:43 inHotKey$4+-3 ] [43])
>> 	  (int_list:REG_BR_PROB 5000 (nil)))
>>     -> 53)
>>    (note 43 42 48 6 [bb 6] NOTE_INSN_BASIC_BLOCK)
>>    (insn 48 43 47 6 (set (reg:SI 2 r2)
>> 	  (mem/u/c:SI (reg:SI 1 r1) [4  S4 A32])) gcc/testsuite/g++.dg/torture/pr34651.C:22 7 {movsi_insn}
>>         (expr_list:REG_DEAD (reg:SI 1 r1)
>> 	  (nil)))
>>    [...]
>>    (code_label 53 169 54 7 6 "" [1 uses])
>>    (note 54 53 12 7 [bb 7] NOTE_INSN_BASIC_BLOCK)
>>    (insn 12 54 57 7 (set:SI (reg/f:SI 2 r2 [orig:46 D.2050 ] [46])
>> 	  (mem/u/c:SI (reg:SI 1 r1) [4  S4 A32])) gcc/testsuite/g++.dg/torture/pr34651.C:22 7 {movsi_insn}
>>         (expr_list:REG_DEAD (reg:SI 1 r1)
>> 	  (expr_list:REG_EQUAL (symbol_ref/f:SI ("*.LC3") [flags 0x2]  <var_decl # *.LC3>)
>> 	      (nil))))
>>
>> where insns 12 and 48 are identical except for the :SI on the SET.
>> This difference prevents us from merging the heads of the two blocks;
>> after removing it we replace the two loads with a single load before
>> the branch.
>>
>> This patch removes the mode argument from gen_rtx_SET and updates
>> all callers.  I used a script to (try to) make sure that all callers
>> really had been caught.  I also built one target per CPU just in case.
>> There were some changes in gcc.dg, g++.dg and gcc.c-torture assembly
>> code for c6x-elf, lm32-elf and v850-elf, but all of them seemed to be
>> code improvements from removing duplicated instructions.  (Other ports
>> also passed spurious modes but apparently not in a way that affects
>> the tests I'd tried.)  Also tested on x86_64-linux-gnu.  OK to install?
>>
>> BTW, I've split the patch up into two, the last bit being a mechanical
>> removal of modes.  (I did it by hand though to try to keep things
>> properly formatted.)
>>
>> Thanks,
>> Richard
>>
>>
>> gcc/
>> 	* rtl.h (always_void_p): New function.
>> 	* gengenrtl.c (always_void_p(: Likewise.
> Typo in the ChangeLog.
>
> non-mechanical part didn't seem to be attached.  I don't expect any 
> problems there, but a quick looksie seems appropriate.

Bah.  Sorry about that.

It's unfortunate that we have two copies of the test -- one on codes
and one on strings -- but that's how everything else in gengenrtl.c
is done.  Maybe a later clean-up.


Index: gcc/genemit.c
===================================================================
--- gcc/genemit.c	2015-05-07 07:59:47.890577327 +0100
+++ gcc/genemit.c	2015-05-07 07:59:47.874577523 +0100
@@ -94,6 +94,7 @@ gen_exp (rtx x, enum rtx_code subroutine
   int i;
   int len;
   const char *fmt;
+  const char *sep = "";
 
   if (x == 0)
     {
@@ -215,7 +216,12 @@ gen_exp (rtx x, enum rtx_code subroutine
 
   printf ("gen_rtx_");
   print_code (code);
-  printf (" (%smode", GET_MODE_NAME (GET_MODE (x)));
+  printf (" (");
+  if (!always_void_p (code))
+    {
+      printf ("%smode", GET_MODE_NAME (GET_MODE (x)));
+      sep = ",\n\t";
+    }
 
   fmt = GET_RTX_FORMAT (code);
   len = GET_RTX_LENGTH (code);
@@ -223,7 +229,7 @@ gen_exp (rtx x, enum rtx_code subroutine
     {
       if (fmt[i] == '0')
 	break;
-      printf (",\n\t");
+      fputs (sep, stdout);
       switch (fmt[i])
 	{
 	case 'e': case 'u':
@@ -254,6 +260,7 @@ gen_exp (rtx x, enum rtx_code subroutine
 	default:
 	  gcc_unreachable ();
 	}
+      sep = ",\n\t";
     }
   printf (")");
 }
Index: gcc/gengenrtl.c
===================================================================
--- gcc/gengenrtl.c	2015-05-07 07:59:47.890577327 +0100
+++ gcc/gengenrtl.c	2015-05-07 08:12:24.281310491 +0100
@@ -116,6 +116,14 @@ special_format (const char *fmt)
 	  || strchr (fmt, 'n') != 0);
 }
 
+/* Return true if CODE always has VOIDmode.  */
+
+static inline bool
+always_void_p (int idx)
+{
+  return strcmp (defs[idx].enumname, "SET") == 0;
+}
+
 /* Return nonzero if the RTL code given by index IDX is one that we should
    generate a gen_rtx_raw_FOO macro for, not gen_rtx_FOO (because gen_rtx_FOO
    is a wrapper in emit-rtl.c).  */
@@ -181,6 +189,7 @@ find_formats (void)
 genmacro (int idx)
 {
   const char *p;
+  const char *sep = "";
   int i;
 
   /* We write a macro that defines gen_rtx_RTLCODE to be an equivalent to
@@ -190,15 +199,25 @@ genmacro (int idx)
     /* Don't define a macro for this code.  */
     return;
 
-  printf ("#define gen_rtx_%s%s(MODE",
+  bool has_mode_p = !always_void_p (idx);
+  printf ("#define gen_rtx_%s%s(",
 	   special_rtx (idx) ? "raw_" : "", defs[idx].enumname);
+  if (has_mode_p)
+    {
+      printf ("MODE");
+      sep = ", ";
+    }
 
   for (p = defs[idx].format, i = 0; *p != 0; p++)
     if (*p != '0')
-      printf (", ARG%d", i++);
-
-  printf (") \\\n  gen_rtx_fmt_%s (%s, (MODE)",
-	  defs[idx].format, defs[idx].enumname);
+      {
+	printf ("%sARG%d", sep, i++);
+	sep = ", ";
+      }
+
+  printf (") \\\n  gen_rtx_fmt_%s (%s, %s",
+	  defs[idx].format, defs[idx].enumname,
+	  has_mode_p ? "(MODE)" : "VOIDmode");
 
   for (p = defs[idx].format, i = 0; *p != 0; p++)
     if (*p != '0')
Index: gcc/rtl.h
===================================================================
--- gcc/rtl.h	2015-05-07 07:59:47.890577327 +0100
+++ gcc/rtl.h	2015-05-07 08:11:56.405652046 +0100
@@ -1787,6 +1787,14 @@ #define COSTS_N_INSNS(N) ((N) * 4)
    not to use an rtx with this cost under any circumstances.  */
 #define MAX_COST INT_MAX
 
+/* Return true if CODE always has VOIDmode.  */
+
+static inline bool
+always_void_p (enum rtx_code code)
+{
+  return code == SET;
+}
+
 /* A structure to hold all available cost information about an rtl
    expression.  */
 struct full_rtx_costs
@@ -3597,5 +3605,4 @@ #define fatal_insn_not_found(insn) \
 /* reginfo.c */
 extern tree GTY(()) global_regs_decl[FIRST_PSEUDO_REGISTER];
 
-
 #endif /* ! GCC_RTL_H */