tree-optimization/105971 - less surprising refs_may_alias_p_2

When DSE asks whether __real a is using __imag a it gets a surprising
result when a is a FUNCTION_DECL.  The following makes sure this case
is less surprising to callers but keeping the bail-out for the
non-decl case where it is true that PTA doesn't track aliases to code
correctly.

2022-06-15  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/105971
	* tree-ssa-alias.cc (refs_may_alias_p_2): Put bail-out for
	FUNCTION_DECL and LABEL_DECL refs after decl-decl disambiguation
	to leak less surprising alias results.

	* gcc.dg/torture/pr106971.c: New testcase.

(cherry picked from commit 8c2733e16ec1c0cdda3db4cdc5ad158a96a658e8)

diff --git a/gcc/testsuite/gcc.dg/torture/pr106971.c b/gcc/testsuite/gcc.dg/torture/pr106971.c
new file mode 100644 (file)
index 0000000..33f2105
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr106971.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+
+void a()
+{
+  int b;
+  int c;
+  int d = (__INTPTR_TYPE__)a;
+  _Complex float *e = (_Complex float *)a;
+  for (;;) {
+    (*e += d) / b ?: 0;
+  }
+}

diff --git a/gcc/tree-ssa-alias.cc b/gcc/tree-ssa-alias.cc
index 063f189..b1e7a2d 100644 (file)
--- a/gcc/tree-ssa-alias.cc
+++ b/gcc/tree-ssa-alias.cc
@@ -2397,15 +2397,6 @@ refs_may_alias_p_2 (ao_ref *ref1, ao_ref *ref2, bool tbaa_p)
       || CONSTANT_CLASS_P (base2))
     return false;
 
-  /* We can end up referring to code via function and label decls.
-     As we likely do not properly track code aliases conservatively
-     bail out.  */
-  if (TREE_CODE (base1) == FUNCTION_DECL
-      || TREE_CODE (base1) == LABEL_DECL
-      || TREE_CODE (base2) == FUNCTION_DECL
-      || TREE_CODE (base2) == LABEL_DECL)
-    return true;
-
   /* Two volatile accesses always conflict.  */
   if (ref1->volatile_p
       && ref2->volatile_p)
@@ -2432,6 +2423,15 @@ refs_may_alias_p_2 (ao_ref *ref1, ao_ref *ref2, bool tbaa_p)
                                  ref2ref, base2, offset2, max_size2,
                                  ref2->size);
 
+  /* We can end up referring to code via function and label decls.
+     As we likely do not properly track code aliases conservatively
+     bail out.  */
+  if (TREE_CODE (base1) == FUNCTION_DECL
+      || TREE_CODE (base1) == LABEL_DECL
+      || TREE_CODE (base2) == FUNCTION_DECL
+      || TREE_CODE (base2) == LABEL_DECL)
+    return true;
+
   /* Handle restrict based accesses.
      ???  ao_ref_base strips inner MEM_REF [&decl], recover from that
      here.  */