PR tree-optimization/92157 - incorrect strcmp() == 0 result for unknown strings

gcc/testsuite/ChangeLog:

	PR tree-optimization/92157
	* gcc.dg/strlenopt-69.c: Disable test failing due to PR 92155.
	* gcc.dg/strlenopt-87.c: New test.

gcc/ChangeLog:

	PR tree-optimization/92157
	* tree-ssa-strlen.c (handle_builtin_string_cmp): Be prepared for
	compute_string_length to return a negative result.

From-SVN: r277194

5 files changed, 130 insertions, 2 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 6ef72d4..ccf870c 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2019-10-18  Martin Sebor  <msebor@redhat.com>
+
+	PR tree-optimization/92157
+	* tree-ssa-strlen.c (handle_builtin_string_cmp): Be prepared for
+	compute_string_length to return a negative result.
+
 2019-10-18  Richard Earnshaw  <rearnsha@arm.com>
 
 	* config/arm/arm.md (negv<SIDI:mode>3): New expansion rule.
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 5875702..1a87247 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,9 @@
+2019-10-18  Martin Sebor  <msebor@redhat.com>
+
+	PR tree-optimization/92157
+	* gcc.dg/strlenopt-69.c: Disable test failing due to PR 92155.
+	* gcc.dg/strlenopt-87.c: New test.
+
 2019-10-18  Richard Earnshaw  <rearnsha@arm.com>
 
 	* gcc.target/arm/negdi-3.c: Update expected output to allow NEGS.
diff --git a/gcc/testsuite/gcc.dg/strlenopt-69.c b/gcc/testsuite/gcc.dg/strlenopt-69.c
index 46ceb9d..9ad8e2e 100644
--- a/gcc/testsuite/gcc.dg/strlenopt-69.c
+++ b/gcc/testsuite/gcc.dg/strlenopt-69.c
@@ -66,11 +66,14 @@ void test_empty_string (void)
   b4[2] = '\0';
   A (0 == strcmp (&a4[2], &b4[2]));
 
+#if 0
+  /* The following isn't handled yet due to PR 92155.  */
   clobber (a4, b4);
 
   memset (a4, 0, sizeof a4);
   memset (b4, 0, sizeof b4);
   A (0 == strcmp (a4, b4));
+#endif
 }
 
 /* Verify that comparison of dynamically created strings with unknown
diff --git a/gcc/testsuite/gcc.dg/strlenopt-87.c b/gcc/testsuite/gcc.dg/strlenopt-87.c
new file mode 100644
index 0000000..082c7b2
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/strlenopt-87.c
@@ -0,0 +1,105 @@
+/* PR tree-optimization/92157 - incorrect strcmp() == 0 result for unknown
+   strings​
+   { dg-do run }
+   { dg-options "-O2 -Wall" } */
+
+#include "strlenopt.h"
+
+
+char a2[2], a3[3];
+
+
+static inline __attribute__ ((always_inline)) int
+verify_not_equal (const char *s, const char *t, int x)
+{
+  int n = x < 0 ? strlen (s) : 0 < x ? strlen (t) : strlen (s) + strlen (t);
+
+  if (strcmp (t, s) == 0)
+    abort ();
+
+  return n;
+}
+
+__attribute__ ((noipa)) int test_a2_s (const char *s)
+{
+  return verify_not_equal (a2, s, 0);
+}
+
+__attribute__ ((noipa)) int test_a2_a3 (void)
+{
+  return verify_not_equal (a2, a3, 0);
+}
+
+__attribute__ ((noipa)) int test_a3_a2 (void)
+{
+  return verify_not_equal (a3, a2, 0);
+}
+
+__attribute__ ((noipa)) int test_s_a2 (const char *s)
+{
+  return verify_not_equal (s, a2, 0);
+}
+
+
+__attribute__ ((noipa)) int test_a2_s_1 (const char *s)
+{
+  return verify_not_equal (a2, s, -1);
+}
+
+__attribute__ ((noipa)) int test_a2_a3_1 (void)
+{
+  return verify_not_equal (a2, a3, -1);
+}
+
+__attribute__ ((noipa)) int test_a3_a2_1 (void)
+{
+  return verify_not_equal (a3, a2, -1);
+}
+
+__attribute__ ((noipa)) int test_s_a2_1 (const char *s)
+{
+  return verify_not_equal (s, a2, -1);
+}
+
+
+__attribute__ ((noipa)) int test_a2_s_2 (const char *s)
+{
+  return verify_not_equal (a2, s, +1);
+}
+
+__attribute__ ((noipa)) int test_a2_a3_2 (void)
+{
+  return verify_not_equal (a2, a3, +1);
+}
+
+__attribute__ ((noipa)) int test_a3_a2_2 (void)
+{
+  return verify_not_equal (a3, a2, +1);
+}
+
+__attribute__ ((noipa)) int test_s_a2_2 (const char *s)
+{
+  return verify_not_equal (s, a2, +1);
+}
+
+int main (void)
+{
+  a2[0] = '1';
+  a3[0] = '1';
+  a3[0] = '2';
+
+  test_a2_s ("");
+  test_a2_a3 ();
+  test_a3_a2 ();
+  test_s_a2 ("");
+
+  test_a2_s_1 ("");
+  test_a2_a3_1 ();
+  test_a3_a2_1 ();
+  test_s_a2_1 ("");
+
+  test_a2_s_2 ("");
+  test_a2_a3_2 ();
+  test_a3_a2_2 ();
+  test_s_a2_2 ("");
+}
diff --git a/gcc/tree-ssa-strlen.c b/gcc/tree-ssa-strlen.c
index d5833f69..4381458 100644
--- a/gcc/tree-ssa-strlen.c
+++ b/gcc/tree-ssa-strlen.c
@@ -3842,7 +3842,7 @@ handle_builtin_string_cmp (gimple_stmt_iterator *gsi)
   HOST_WIDE_INT arysiz1 = -1, arysiz2 = -1;
 
   if (idx1)
-    cstlen1 = compute_string_length (idx1) + 1;
+    cstlen1 = compute_string_length (idx1);
   else
     arysiz1 = determine_min_objsize (arg1);
 
@@ -3853,13 +3853,21 @@ handle_builtin_string_cmp (gimple_stmt_iterator *gsi)
 
   /* Repeat for the second argument.  */
   if (idx2)
-    cstlen2 = compute_string_length (idx2) + 1;
+    cstlen2 = compute_string_length (idx2);
   else
     arysiz2 = determine_min_objsize (arg2);
 
   if (cstlen2 < 0 && arysiz2 < 0)
     return false;
 
+  if (cstlen1 < 0 && cstlen2 < 0)
+    return false;
+
+  if (cstlen1 >= 0)
+    ++cstlen1;
+  if (cstlen2 >= 0)
+    ++cstlen2;
+
   /* The exact number of characters to compare.  */
   HOST_WIDE_INT cmpsiz = bound < 0 ? cstlen1 < 0 ? cstlen2 : cstlen1 : bound;
   /* The size of the array in which the unknown string is stored.  */