[gcc r11-3489] optabs: Don't reuse target for multi-word expansions if it overlaps operand(s) [PR97073]

[gcc r11-3489] optabs: Don't reuse target for multi-word expansions if it overlaps operand(s) [PR97073]

[Jakub Jelinek]

https://gcc.gnu.org/g:a4b31d5807f2bc67c8999b3d53369cf2a5c6e1ec

commit r11-3489-ga4b31d5807f2bc67c8999b3d53369cf2a5c6e1ec
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Sun Sep 27 23:18:26 2020 +0200

    optabs: Don't reuse target for multi-word expansions if it overlaps operand(s) [PR97073]
    
    The following testcase is miscompiled on i686-linux, because
    we try to expand a double-word bitwise logic operation with op0
    being a (mem:DI u) and target (mem:DI u+4), i.e. partial overlap, and
    thus end up with:
            movl    4(%esp), %eax
            andl    u, %eax
            movl    %eax, u+4
    ! movl u+4, %eax optimized out
            andl    8(%esp), %eax
            movl    %eax, u+8
    rather than with the desired:
            movl    4(%esp), %edx
            movl    8(%esp), %eax
            andl    u, %edx
            andl    u+4, %eax
            movl    %eax, u+8
            movl    %edx, u+4
    because the store of the first word to target overwrites the second word of
    the operand.
    expand_binop for this (and several similar places) already check for target
    == op0 or target == op1, this patch just adds reg_overlap_mentioned_p calls
    next to it.
    Pedantically, at least for some of these it might be sufficient to force
    a different target if there is overlap but target is not rtx_equal_p to
    the operand (e.g. in this bitwise logical case, but e.g. not in the shift
    cases where there is reordering), though that would go against the
    preexisting target == op? checks and the rationale that REG_EQUAL notes in
    that case isn't correct.
    
    2020-09-27  Jakub Jelinek  <jakub@redhat.com>
    
            PR middle-end/97073
            * optabs.c (expand_binop, expand_absneg_bit, expand_unop,
            expand_copysign_bit): Check reg_overlap_mentioned_p between target
            and operand(s) and if it returns true, force a pseudo as target.
    
            * gcc.c-torture/execute/pr97073.c: New test.

Diff:
---
 gcc/optabs.c                                  | 14 +++++++++++++-
 gcc/testsuite/gcc.c-torture/execute/pr97073.c | 21 +++++++++++++++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/gcc/optabs.c b/gcc/optabs.c
index 8e844028d92..8ad7f4bef21 100644
--- a/gcc/optabs.c
+++ b/gcc/optabs.c
@@ -1395,6 +1395,8 @@ expand_binop (machine_mode mode, optab binoptab, rtx op0, rtx op1,
       if (target == 0
 	  || target == op0
 	  || target == op1
+	  || reg_overlap_mentioned_p (target, op0)
+	  || reg_overlap_mentioned_p (target, op1)
 	  || !valid_multiword_target_p (target))
 	target = gen_reg_rtx (int_mode);
 
@@ -1475,6 +1477,8 @@ expand_binop (machine_mode mode, optab binoptab, rtx op0, rtx op1,
 	  if (target == 0
 	      || target == op0
 	      || target == op1
+	      || reg_overlap_mentioned_p (target, op0)
+	      || reg_overlap_mentioned_p (target, op1)
 	      || !valid_multiword_target_p (target))
 	    target = gen_reg_rtx (int_mode);
 
@@ -1533,6 +1537,8 @@ expand_binop (machine_mode mode, optab binoptab, rtx op0, rtx op1,
 	  || target == op0
 	  || target == op1
 	  || !REG_P (target)
+	  || reg_overlap_mentioned_p (target, op0)
+	  || reg_overlap_mentioned_p (target, op1)
 	  || !valid_multiword_target_p (target))
 	target = gen_reg_rtx (int_mode);
 
@@ -2670,6 +2676,7 @@ expand_absneg_bit (enum rtx_code code, scalar_float_mode mode,
 
   if (target == 0
       || target == op0
+      || reg_overlap_mentioned_p (target, op0)
       || (nwords > 1 && !valid_multiword_target_p (target)))
     target = gen_reg_rtx (mode);
 
@@ -2951,7 +2958,10 @@ expand_unop (machine_mode mode, optab unoptab, rtx op0, rtx target,
       int i;
       rtx_insn *insns;
 
-      if (target == 0 || target == op0 || !valid_multiword_target_p (target))
+      if (target == 0
+	  || target == op0
+	  || reg_overlap_mentioned_p (target, op0)
+	  || !valid_multiword_target_p (target))
 	target = gen_reg_rtx (int_mode);
 
       start_sequence ();
@@ -3472,6 +3482,8 @@ expand_copysign_bit (scalar_float_mode mode, rtx op0, rtx op1, rtx target,
   if (target == 0
       || target == op0
       || target == op1
+      || reg_overlap_mentioned_p (target, op0)
+      || reg_overlap_mentioned_p (target, op1)
       || (nwords > 1 && !valid_multiword_target_p (target)))
     target = gen_reg_rtx (mode);
 
diff --git a/gcc/testsuite/gcc.c-torture/execute/pr97073.c b/gcc/testsuite/gcc.c-torture/execute/pr97073.c
new file mode 100644
index 00000000000..1955e6b8bd2
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/execute/pr97073.c
@@ -0,0 +1,21 @@
+/* PR middle-end/97073 */
+/* { dg-additional-options "-mno-stv" { target i?86-*-* x86_64-*-* } } */
+
+typedef unsigned long long L;
+union U { L i; struct T { unsigned k; L l; } j; } u;
+
+__attribute__((noinline,noclone)) void
+foo (L x)
+{
+  u.j.l = u.i & x;
+}
+
+int
+main ()
+{
+  u.i = 5;
+  foo (-1ULL);
+  if (u.j.l != 5)
+    __builtin_abort ();
+  return 0;
+}