[gcc(refs/users/aoliva/heads/testme)] relax ifcombine to accept vuses

[Alexandre Oliva]

https://gcc.gnu.org/g:7b7dfff4b174765248fcf275dc8fde9c78352ad8

commit 7b7dfff4b174765248fcf275dc8fde9c78352ad8
Author: Alexandre Oliva <oliva@gnu.org>
Date:   Fri Sep 13 21:43:15 2024 -0300

    relax ifcombine to accept vuses

Diff:
---
 gcc/config/i386/t-i386               |  2 ++
 gcc/testsuite/gcc.dg/field-merge-6.c | 26 ++++++++++++++++++++++++++
 gcc/tree-ssa-ifcombine.cc            |  2 +-
 3 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/gcc/config/i386/t-i386 b/gcc/config/i386/t-i386
index bf4ae109af98..1b904787ec62 100644
--- a/gcc/config/i386/t-i386
+++ b/gcc/config/i386/t-i386
@@ -79,3 +79,5 @@ s-i386-bt: $(srcdir)/config/i386/i386-builtin-types.awk \
 	$(AWK) -f $^ > tmp-bt.inc
 	$(SHELL) $(srcdir)/../move-if-change tmp-bt.inc i386-builtin-types.inc
 	$(STAMP) $@
+
+insn-attrtab.o-warn = -Wno-error
diff --git a/gcc/testsuite/gcc.dg/field-merge-6.c b/gcc/testsuite/gcc.dg/field-merge-6.c
new file mode 100644
index 000000000000..7fd48a138d14
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/field-merge-6.c
@@ -0,0 +1,26 @@
+/* { dg-do run } */
+/* { dg-options "-O" } */
+/* { dg-shouldfail } */
+
+/* Check that the third compare won't be pulled ahead of the second one and
+   prevent, which would prevent the NULL pointer dereference that should cause
+   the execution to fail.  */
+
+struct s {
+  char a, b;
+  int *p;
+};
+
+struct s a = { 0, 1, 0 };
+struct s b = { 0, 0, 0 };
+
+int f () {
+  return (a.a != b.a
+	  || *b.p != *a.p
+	  || a.b != b.b);
+}
+
+int main() {
+  f ();
+  return 0;
+}
diff --git a/gcc/tree-ssa-ifcombine.cc b/gcc/tree-ssa-ifcombine.cc
index 61480e5fa894..7678c87e0170 100644
--- a/gcc/tree-ssa-ifcombine.cc
+++ b/gcc/tree-ssa-ifcombine.cc
@@ -129,7 +129,7 @@ bb_no_side_effects_p (basic_block bb)
       enum tree_code rhs_code;
       if (gimple_has_side_effects (stmt)
 	  || gimple_could_trap_p (stmt)
-	  || gimple_vuse (stmt)
+	  /* || gimple_vuse (stmt) */
 	  /* We need to rewrite stmts with undefined overflow to use
 	     unsigned arithmetic but cannot do so for signed division.  */
 	  || ((ass = dyn_cast <gassign *> (stmt))