[gcc r10-10796] Darwin, rs6000: Amend lo_sum use for forced constants [PR104117].

[gcc r10-10796] Darwin, rs6000: Amend lo_sum use for forced constants [PR104117].

[Iain D Sandoe]

https://gcc.gnu.org/g:cfad91385ae0f92eedda1fff5f6f4b23da9f1f1b

commit r10-10796-gcfad91385ae0f92eedda1fff5f6f4b23da9f1f1b
Author: Iain Sandoe <iain@sandoe.co.uk>
Date:   Mon Feb 7 15:36:35 2022 +0000

    Darwin, rs6000: Amend lo_sum use for forced constants [PR104117].
    
    Two issues resulted in this PR, which manifests when we force a constant into
    memory in LRA (in PIC code on Darwin).  The presence of such forced constants
    is quite dependent on other RTL optimisations, and it is easy for the issue to
    become latent for a specific case.
    
    First, in the Darwin-specific rs6000 backend code, we were not being careful
    enough in rejecting invalid symbolic addresses.  Specifically, when generating
    PIC code, we require a SYMBOL_REF to be wrapped in an UNSPEC_MACHOPIC_OFFSET.
    
    We now split the Darwin high/low selectors into two:
     1. One that handles non-PIC addresses (kernel mode, mdynamic-no-pic).
     2. One that handles PIC addresses and rejects SYMBOL_REFs unless they are
        suitably wrapped in the MACHOPIC_OFFSET unspec.
    
    The second case is handled by providing a new predicate (macho_pic_address)
    that checks the requirements.
    
    Backported from 4c3792d448964f7bd99e7eac2c29c9eb7c2bfb84 and
    f1b3e3853329b58fb2e50c17487df2ecbc4a5608
    
    Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
    Co-authored-by: Vladimir Makarov <vmakarov@redhat.com>
    
            PR target/104117
    
    gcc/ChangeLog:
    
            * config/rs6000/rs6000.c (darwin_rs6000_legitimate_lo_sum_const_p):
            Check for UNSPEC_MACHOPIC_OFFSET wrappers on symbolic addresses when
            emitting PIC code.
            (legitimate_lo_sum_address_p): Likewise.
            (rs6000_legitimize_address): Do not apply the TLS processing to
            Darwin.
            * config/rs6000/darwin.md (@machopic_high_<mode>): New.
            (@machopic_low_<mode>): New.
            * config/rs6000/predicates.md (macho_pic_address): New.

Diff:
---
 gcc/config/rs6000/darwin.md     | 19 +++++++++++++++----
 gcc/config/rs6000/predicates.md | 14 ++++++++++++++
 gcc/config/rs6000/rs6000.c      | 40 +++++++++++++++++++++++++++++++++++++---
 3 files changed, 66 insertions(+), 7 deletions(-)

diff --git a/gcc/config/rs6000/darwin.md b/gcc/config/rs6000/darwin.md
index 05948c89202..a47db126651 100644
--- a/gcc/config/rs6000/darwin.md
+++ b/gcc/config/rs6000/darwin.md
@@ -121,21 +121,32 @@ You should have received a copy of the GNU General Public License
    stw %0,lo16(%2)(%1)"
   [(set_attr "type" "store")])
 
-;; 64-bit MachO load/store support
-
 ;; Mach-O PIC.
 
 (define_insn "@macho_high_<mode>"
   [(set (match_operand:P 0 "gpc_reg_operand" "=b*r")
 	(high:P (match_operand 1 "" "")))]
-  "TARGET_MACHO && (DEFAULT_ABI == ABI_DARWIN)"
+  "TARGET_MACHO && (DEFAULT_ABI == ABI_DARWIN) && !flag_pic"
   "lis %0,ha16(%1)")
 
 (define_insn "@macho_low_<mode>"
   [(set (match_operand:P 0 "gpc_reg_operand" "=r")
 	(lo_sum:P (match_operand:P 1 "gpc_reg_operand" "b")
 		   (match_operand 2 "" "")))]
-   "TARGET_MACHO && (DEFAULT_ABI == ABI_DARWIN)"
+   "TARGET_MACHO && (DEFAULT_ABI == ABI_DARWIN) && !flag_pic"
+   "la %0,lo16(%2)(%1)")
+
+(define_insn "@machopic_high_<mode>"
+  [(set (match_operand:P 0 "gpc_reg_operand" "=b*r")
+	(high:P (match_operand 1 "macho_pic_address" "")))]
+  "TARGET_MACHO && flag_pic"
+  "lis %0,ha16(%1)")
+
+(define_insn "@machopic_low_<mode>"
+  [(set (match_operand:P 0 "gpc_reg_operand" "=r")
+	(lo_sum:P (match_operand:P 1 "gpc_reg_operand" "b")
+		   (match_operand 2 "macho_pic_address" "")))]
+   "TARGET_MACHO && flag_pic"
    "la %0,lo16(%2)(%1)")
 
 (define_split
diff --git a/gcc/config/rs6000/predicates.md b/gcc/config/rs6000/predicates.md
index fad45a6e1ac..7161c10d5a8 100644
--- a/gcc/config/rs6000/predicates.md
+++ b/gcc/config/rs6000/predicates.md
@@ -1864,3 +1864,17 @@
 {
   return address_is_prefixed (XEXP (op, 0), mode, NON_PREFIXED_DEFAULT);
 })
+
+;; Return true if the operand is a valid Mach-O pic address.
+;;
+(define_predicate "macho_pic_address"
+  (match_code "const,unspec")
+{
+  if (GET_CODE (op) == CONST)
+    op = XEXP (op, 0);
+
+  if (GET_CODE (op) == UNSPEC && XINT (op, 1) == UNSPEC_MACHOPIC_OFFSET)
+    return CONSTANT_P (XVECEXP (op, 0, 0));
+  else
+    return false;
+})
diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
index a43438ad925..45a406a5803 100644
--- a/gcc/config/rs6000/rs6000.c
+++ b/gcc/config/rs6000/rs6000.c
@@ -7582,8 +7582,14 @@ darwin_rs6000_legitimate_lo_sum_const_p (rtx x, machine_mode mode)
   if (GET_CODE (x) == CONST)
     x = XEXP (x, 0);
 
+  /* If we are building PIC code, then any symbol must be wrapped in an
+     UNSPEC_MACHOPIC_OFFSET so that it will get the picbase subtracted.  */
+  bool machopic_offs_p = false;
   if (GET_CODE (x) == UNSPEC && XINT (x, 1) == UNSPEC_MACHOPIC_OFFSET)
-    x =  XVECEXP (x, 0, 0);
+    {
+      x =  XVECEXP (x, 0, 0);
+      machopic_offs_p = true;
+    }
 
   rtx sym = NULL_RTX;
   unsigned HOST_WIDE_INT offset = 0;
@@ -7614,6 +7620,9 @@ darwin_rs6000_legitimate_lo_sum_const_p (rtx x, machine_mode mode)
   if (sym)
     {
       tree decl = SYMBOL_REF_DECL (sym);
+      /* As noted above, PIC code cannot use a bare SYMBOL_REF.  */
+      if (TARGET_MACHO && flag_pic && !machopic_offs_p)
+	return false;
 #if TARGET_MACHO
       if (MACHO_SYMBOL_INDIRECTION_P (sym))
       /* The decl in an indirection symbol is the original one, which might
@@ -8201,7 +8210,7 @@ legitimate_lo_sum_address_p (machine_mode mode, rtx x, int strict)
     return false;
   x = XEXP (x, 1);
 
-  if (TARGET_ELF || TARGET_MACHO)
+  if (TARGET_ELF)
     {
       bool large_toc_ok;
 
@@ -8227,7 +8236,32 @@ legitimate_lo_sum_address_p (machine_mode mode, rtx x, int strict)
 
       return CONSTANT_P (x) || large_toc_ok;
     }
+  else if (TARGET_MACHO)
+    {
+      if (GET_MODE_NUNITS (mode) != 1)
+	return false;
+      if (GET_MODE_SIZE (mode) > UNITS_PER_WORD
+	  && !(/* see above  */
+	       TARGET_HARD_FLOAT && (mode == DFmode || mode == DDmode)))
+	return false;
+#if TARGET_MACHO
+      if (MACHO_DYNAMIC_NO_PIC_P || !flag_pic)
+	return CONSTANT_P (x);
+#endif
+      /* Macho-O PIC code from here.  */
+      if (GET_CODE (x) == CONST)
+	x = XEXP (x, 0);
+
+      /* SYMBOL_REFs need to be wrapped in an UNSPEC_MACHOPIC_OFFSET.  */
+      if (SYMBOL_REF_P (x))
+	return false;
 
+      /* So this is OK if the wrapped object is const.  */
+      if (GET_CODE (x) == UNSPEC
+	  && XINT (x, 1) == UNSPEC_MACHOPIC_OFFSET)
+	return CONSTANT_P (XVECEXP (x, 0, 0));
+      return CONSTANT_P (x);
+    }
   return false;
 }
 
@@ -8281,7 +8315,7 @@ rs6000_legitimize_address (rtx x, rtx oldx ATTRIBUTE_UNUSED,
       else
 	return force_reg (Pmode, x);
     }
-  if (SYMBOL_REF_P (x))
+  if (SYMBOL_REF_P (x) && !TARGET_MACHO)
     {
       enum tls_model model = SYMBOL_REF_TLS_MODEL (x);
       if (model != 0)