[gcc/devel/c++-modules] PR tree-optimization/93213 - wrong code with -Og -foptimize-strlen

[Nathan Sidwell]

https://gcc.gnu.org/g:e13f37d9f7600d337f8a4589b5f985ded9e05852

commit e13f37d9f7600d337f8a4589b5f985ded9e05852
Author: Martin Sebor <msebor@redhat.com>
Date:   Mon Jan 13 13:20:41 2020 +0000

    PR tree-optimization/93213 - wrong code with -Og -foptimize-strlen
    
    gcc/testsuite/ChangeLog:
    
    	PR tree-optimization/93213
    	* gcc.c-torture/execute/pr93213.c: New test.
    
    gcc/ChangeLog:
    
    	PR tree-optimization/93213
    	* tree-ssa-strlen.c (handle_store): Only allow single-byte nul-over-nul
    	stores to be eliminated.

Diff:
---
 gcc/ChangeLog                                 |  6 ++++
 gcc/testsuite/ChangeLog                       |  5 +++
 gcc/testsuite/gcc.c-torture/execute/pr93213.c | 50 +++++++++++++++++++++++++++
 gcc/tree-ssa-strlen.c                         |  6 ++--
 4 files changed, 64 insertions(+), 3 deletions(-)

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index fc25469..2a4b03a 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2020-01-13  Martin Sebor  <msebor@redhat.com>
+
+	PR tree-optimization/93213
+	* tree-ssa-strlen.c (handle_store): Only allow single-byte nul-over-nul
+	stores to be eliminated.
+
 2020-01-13  Martin Liska  <mliska@suse.cz>
 
 	* opts.c (print_help): Do not print CL_PARAM
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index cccc285..f14638c 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2020-01-13  Martin Sebor  <msebor@redhat.com>
+
+	PR tree-optimization/93213
+	* gcc.c-torture/execute/pr93213.c: New test.
+
 2020-01-10  Thomas Schwinge  <thomas@codesourcery.com>
 
 	* c-c++-common/goacc/host_data-1.c: Extend.
diff --git a/gcc/testsuite/gcc.c-torture/execute/pr93213.c b/gcc/testsuite/gcc.c-torture/execute/pr93213.c
new file mode 100644
index 0000000..86d0465
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/execute/pr93213.c
@@ -0,0 +1,50 @@
+/* PR tree-optimization/93213 - wrong code on a multibyte store with
+   -Og -foptimize-strlen
+   { dg-require-effective-target int128 }
+   { dg-additional-options "-Og -foptimize-strlen" } */
+
+typedef unsigned __INT16_TYPE__ u16;
+typedef unsigned __INT32_TYPE__ u32;
+typedef unsigned __int128 u128;
+
+static inline u128
+foo (u16 u16_1, u32 u32_1, u128 u128_1)
+{
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+  u128 u128_0 = 0;
+  u128_1 -= __builtin_mul_overflow (u32_1, u16_1, &u32_1);
+  __builtin_memmove (&u16_1, &u128_0, 2);
+  __builtin_memmove (&u16_1, &u128_1, 1);
+  return u16_1;
+#else
+  return 0xff;
+#endif
+}
+
+__attribute__ ((noipa)) void
+bar (void)
+{
+  char a[] = { 1, 2 };
+  const char b[] = { 0, 0 };
+  const char c[] = { 2 };
+  __builtin_memcpy (a, b, 2);
+  // The above is transformed into
+  //   MEM <short unsigned int> [(char * {ref-all})&a] = 0;
+  // which was then dropped because of the non-nul store below.
+  __builtin_memcpy (a, c, 1);
+
+  volatile char *p = a;
+  if (p[0] != 2 || p[1] != 0)
+    __builtin_abort ();
+}
+
+int
+main (void)
+{
+  u16 x = foo (-1, -1, 0);
+  if (x != 0xff)
+    __builtin_abort ();
+
+  bar ();
+  return 0;
+}
diff --git a/gcc/tree-ssa-strlen.c b/gcc/tree-ssa-strlen.c
index 4f2a0ad..ad9e989 100644
--- a/gcc/tree-ssa-strlen.c
+++ b/gcc/tree-ssa-strlen.c
@@ -5239,10 +5239,10 @@ handle_store (gimple_stmt_iterator *gsi, bool *zero_write,
 	}
     }
 
-  if (si != NULL && offset == 0 && storing_all_zeros_p)
+  if (si != NULL && offset == 0 && storing_all_zeros_p && lenrange[2] == 1)
     {
-      /* Allow adjust_last_stmt to remove it if the stored '\0'
-	 is immediately overwritten.  */
+      /* For single-byte stores only, allow adjust_last_stmt to remove
+	 the statement if the stored '\0' is immediately overwritten.  */
       laststmt.stmt = stmt;
       laststmt.len = build_int_cst (size_type_node, 1);
       laststmt.stridx = si->idx;