From: Richard Biener <rguenther@suse.de>
Date: Tue, 4 Jul 2023 10:52:27 +0000 (+0200)
Subject: tree-optimization/110491 - PHI-OPT and undefs
X-Git-Tag: basepoints/gcc-15~7843
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=819285ef10a87d663f8c181c06aa88d1d9f75aed;p=thirdparty%2Fgcc.git

tree-optimization/110491 - PHI-OPT and undefs

The following makes sure to not make conditional undefs in PHI arguments
unconditional by folding cond ? arg1 : arg2.

	PR tree-optimization/110491
	* tree-ssa-phiopt.cc (match_simplify_replacement): Check
	whether the PHI args are possibly undefined before folding
	the COND_EXPR.

	* gcc.dg/torture/pr110491.c: New testcase.
---

diff --git a/gcc/testsuite/gcc.dg/torture/pr110491.c b/gcc/testsuite/gcc.dg/torture/pr110491.c
new file mode 100644
index 000000000000..00b3bdfc122e
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr110491.c
@@ -0,0 +1,29 @@
+/* { dg-do run } */
+
+int a, c, d, e;
+short b;
+void f(int *g) { c &= *g; }
+void h(void);
+void i() {
+  a = 1;
+  h();
+  f(&a);
+}
+void h() {
+  int *j = &c;
+  *j = 5;
+k:
+  for (; 4 + b <= 0;)
+    ;
+  for (; d;) {
+    c = e == 0;
+    goto k;
+  }
+}
+int main()
+{
+  i();
+  if (c != 1)
+    __builtin_abort ();
+  return 0;
+}
diff --git a/gcc/tree-ssa-phiopt.cc b/gcc/tree-ssa-phiopt.cc
index 31a7c39e4052..467c9fd108a8 100644
--- a/gcc/tree-ssa-phiopt.cc
+++ b/gcc/tree-ssa-phiopt.cc
@@ -785,6 +785,13 @@ match_simplify_replacement (basic_block cond_bb, basic_block middle_bb,
       arg_false = arg0;
     }
 
+  /* Do not make conditional undefs unconditional.  */
+  if ((TREE_CODE (arg_true) == SSA_NAME
+       && ssa_name_maybe_undef_p (arg_true))
+      || (TREE_CODE (arg_false) == SSA_NAME
+	  && ssa_name_maybe_undef_p (arg_false)))
+    return false;
+
   tree type = TREE_TYPE (gimple_phi_result (phi));
   result = gimple_simplify_phiopt (early_p, type, stmt,
 				   arg_true, arg_false,