PR tree-optimization/92412 - excessive errno aliasing assumption defeats optimization

gcc/ChangeLog:

	PR tree-optimization/92412
	* targhooks.c (default_ref_may_alias_errno): Errono can only alias
	extern variables.

gcc/testsuite/ChangeLog:

	PR tree-optimization/92412
	* gcc.dg/strlenopt-91.c: New test.

From-SVN: r278099

4 files changed, 139 insertions, 2 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index ddd9817690d..a434f25311c 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,11 @@
 2019-11-12  Martin Sebor  <msebor@redhat.com>
 
+	PR tree-optimization/92412
+	* targhooks.c (default_ref_may_alias_errno): Errono can only alias
+	extern variables.
+
+2019-11-12  Martin Sebor  <msebor@redhat.com>
+
 	PR middle-end/83688
 	* gimple-ssa-sprintf.c (format_result::alias_info): New struct.
 	(directive::argno): New member.
diff --git a/gcc/targhooks.c b/gcc/targhooks.c
index 822a0313e9e..b6443d204a6 100644
--- a/gcc/targhooks.c
+++ b/gcc/targhooks.c
@@ -1414,9 +1414,11 @@ default_ref_may_alias_errno (ao_ref *ref)
   if (TYPE_UNSIGNED (TREE_TYPE (base))
       || TYPE_MODE (TREE_TYPE (base)) != TYPE_MODE (integer_type_node))
     return false;
-  /* The default implementation assumes an errno location
-     declaration is never defined in the current compilation unit.  */
+  /* The default implementation assumes an errno location declaration
+     is never defined in the current compilation unit and may not be
+     aliased by a local variable.  */
   if (DECL_P (base)
+      && DECL_EXTERNAL (base)
       && !TREE_STATIC (base))
     return true;
   else if (TREE_CODE (base) == MEM_REF
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 460ca2bbacb..584ccd7e143 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,5 +1,10 @@
 2019-11-12  Martin Sebor  <msebor@redhat.com>
 
+	PR tree-optimization/92412
+	* gcc.dg/strlenopt-91.c: New test.
+
+2019-11-12  Martin Sebor  <msebor@redhat.com>
+
 	PR tree-optimization/35503
 	* gcc.dg/tree-ssa/builtin-sprintf-warn-23.c: New test.
 
diff --git a/gcc/testsuite/gcc.dg/strlenopt-91.c b/gcc/testsuite/gcc.dg/strlenopt-91.c
new file mode 100644
index 00000000000..2381d03e44a
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/strlenopt-91.c
@@ -0,0 +1,124 @@
+/* PR tree-optimization/92412 - excessive errno aliasing assumption defeats
+   optimization
+   { dg-do compile }
+   { dg-options "-O2 -Wall -fdump-tree-optimized" } */
+
+typedef __SIZE_TYPE__ size_t;
+
+extern void* alloca (size_t);
+extern void* calloc (size_t, size_t);
+extern void* malloc (size_t);
+
+extern const char exta[4];
+static char stata[] = "123";
+
+void sink (const void*, ...);
+
+#define T(ptr, alloc) do {						\
+    const char *p = ptr;						\
+    if (p[0] != '1' || p[1] != '2' || p[2] != '3' || p[3] != '\0'	\
+	|| __builtin_strlen (p) != 3)					\
+      return;								\
+									\
+    void *q = alloc;							\
+    __builtin_strcpy (q, p);						\
+									\
+    if (p[0] != '1' || p[1] != '2' || p[2] != '3' || p[3] != '\0'	\
+	|| __builtin_strlen (p) != 3					\
+	|| __builtin_strlen (q) != 3)					\
+      __builtin_abort ();						\
+									\
+    sink (p, q);							\
+  } while (0)
+
+
+void alloca_test_local (unsigned n)
+{
+  char loca[] = "123";
+  T (loca, alloca (n));
+}
+
+void alloca_test_extern_const (unsigned n)
+{
+  T (exta, alloca (n));
+}
+
+void alloca_test_static (unsigned n)
+{
+  T (stata, alloca (n));
+}
+
+
+// Verify fix for PR tree-optimization/92412.
+void calloc_test_local (unsigned m, unsigned n)
+{
+  char loca[] = "123";
+  T (loca, calloc (m, n));
+}
+
+void calloc_test_extern_const (unsigned m, unsigned n)
+{
+  T (exta, calloc (m, n));
+}
+
+void calloc_test_static (unsigned m, unsigned n)
+{
+  T (stata, calloc (m, n));
+}
+
+
+// Verify fix for PR tree-optimization/92412.
+void malloc_test_local (unsigned n)
+{
+  char loca[] = "123";
+  T (loca, malloc (n));
+}
+
+void malloc_test_extern_const (unsigned n)
+{
+  T (exta, malloc (n));
+}
+
+void malloc_test_static (unsigned n)
+{
+  T (stata, malloc (n));
+}
+
+
+#undef T
+#define T(ptr, n) do {							\
+    const char *p = ptr;						\
+    if (p[0] != '1' || p[1] != '2' || p[2] != '3' || p[3] != '\0'	\
+	|| __builtin_strlen (p) != 3)					\
+      return;								\
+									\
+    char vla[n];							\
+    char *q = vla;							\
+    __builtin_strcpy (q, p);						\
+									\
+    if (p[0] != '1' || p[1] != '2' || p[2] != '3' || p[3] != '\0'	\
+	|| __builtin_strlen (p) != 3					\
+	|| __builtin_strlen (q) != 3)					\
+      __builtin_abort ();						\
+									\
+    sink (p, vla);							\
+  } while (0)
+
+
+void vla_test_local (unsigned n)
+{
+  char loca[] = "123";
+  T (loca, n);
+}
+
+void vla_test_extern_const (unsigned n)
+{
+  T (exta, n);
+}
+
+void vla_test_static (unsigned n)
+{
+  T (stata, n);
+}
+
+/* { dg-final { scan-tree-dump-not "abort" "optimized" } } */