tree-ssa-dse.c (initialize_ao_ref_for_dse): Handle strncpy.

	* tree-ssa-dse.c (initialize_ao_ref_for_dse): Handle
	strncpy.  Drop some trivial dead code.
	(maybe_trim_memstar_call): Handle strncpy.

	* gcc.dg/tree-ssa/ssa-dse-37.c: New test.
	* gcc.dg/tree-ssa/ssa-dse-38.c: New test.

From-SVN: r273606

gcc/ChangeLog

+2019-07-19  Jeff Law  <law@redhat.com>
+
+	* tree-ssa-dse.c (initialize_ao_ref_for_dse): Handle
+	strncpy.  Drop some trivial dead code.
+	(maybe_trim_memstar_call): Handle strncpy.
+
 2019-07-19  Richard Biener  <rguenther@suse.de>
 
 	PR tree-optimization/91211

gcc/testsuite/ChangeLog

+2019-07-19  Jeff Law  <law@redhat.com>
+
+	* gcc.dg/tree-ssa/ssa-dse-37.c: New test.
+	* gcc.dg/tree-ssa/ssa-dse-38.c: New test.
+
 2019-07-19  Richard Biener  <rguenther@suse.de>
 
 	PR tree-optimization/91211

gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-37.c

+/* { dg-options "-O2 -fdump-tree-dse-details -fno-tree-fre" } */
+
+
+#ifndef SCOPE
+#define SCOPE
+#endif
+
+extern void frob (char *);
+
+void g (char *s)
+{
+  SCOPE char a[8];
+  __builtin_strncpy (a, s, sizeof a);
+  __builtin_memset (a, 0, sizeof a); 
+  frob (a);
+}
+
+void h (char *s)
+{
+  SCOPE char a[8];
+  __builtin_memset (a, 0, sizeof a); 
+  __builtin_strncpy (a, s, sizeof a);
+  frob (a);
+}
+
+void i (char *s)
+{
+  SCOPE char a[8];
+  __builtin_strncpy (a, s, sizeof a);
+  __builtin_memset (a, 0, sizeof a - 5); 
+  frob (a);
+}
+
+void j (char *s)
+{
+  SCOPE char a[8];
+  __builtin_memset (a, 0, sizeof a); 
+  __builtin_strncpy (a, s, sizeof a - 5);
+  frob (a);
+}
+
+void l (char *s)
+{
+  SCOPE char a[8];
+  __builtin_strncpy (a, s, sizeof a);
+  __builtin_memset (a + 2, 0, sizeof a - 2); 
+  frob (a);
+}
+
+void m (char *s)
+{
+  SCOPE char a[8];
+  __builtin_memset (a, 0, sizeof a); 
+  __builtin_strncpy (a + 2, s, sizeof a - 2);
+  frob (a);
+}
+
+/* { dg-final { scan-tree-dump-times "Deleted dead call" 2 "dse1" } } */
+/* { dg-final { scan-tree-dump-times "Trimming statement " 4 "dse1" } } */
+

gcc/testsuite/gcc.dg/tree-ssa/ssa-dse-38.c

+/* { dg-options "-O2 -fdump-tree-dse-details -fno-tree-fre" } */
+
+
+/* This changes the scope of the destination object and exposes
+   missed optimizations in DSE.  */
+#define SCOPE extern
+#include "ssa-dse-37.c"
+
+/* { dg-final { scan-tree-dump-times "Deleted dead call" 2 "dse1" { xfail *-*-* } } } */
+/* { dg-final { scan-tree-dump-times "Trimming statement " 4 "dse1" { xfail *-*-* } } } */
+
+

gcc/tree-ssa-dse.c

@@ -113,10 +113,10 @@ initialize_ao_ref_for_dse (gimple *stmt, ao_ref *write)
 	case BUILT_IN_MEMCPY_CHK:
 	case BUILT_IN_MEMMOVE_CHK:
 	case BUILT_IN_MEMSET_CHK:
+	case BUILT_IN_STRNCPY:
+	case BUILT_IN_STRNCPY_CHK:
 	  {
-	    tree size = NULL_TREE;
-	    if (gimple_call_num_args (stmt) == 3)
-	      size = gimple_call_arg (stmt, 2);
+	    tree size = gimple_call_arg (stmt, 2);
 	    tree ptr = gimple_call_arg (stmt, 0);
 	    ao_ref_init_from_ptr_and_size (write, ptr, size);
 	    return true;
@@ -469,8 +469,10 @@ maybe_trim_memstar_call (ao_ref *ref, sbitmap live, gimple *stmt)
     {
     case BUILT_IN_MEMCPY:
     case BUILT_IN_MEMMOVE:
+    case BUILT_IN_STRNCPY:
     case BUILT_IN_MEMCPY_CHK:
     case BUILT_IN_MEMMOVE_CHK:
+    case BUILT_IN_STRNCPY_CHK:
       {
 	int head_trim, tail_trim;
 	compute_trims (ref, live, &head_trim, &tail_trim, stmt);
@@ -966,9 +968,11 @@ dse_dom_walker::dse_optimize_stmt (gimple_stmt_iterator *gsi)
 	{
 	case BUILT_IN_MEMCPY:
 	case BUILT_IN_MEMMOVE:
+	case BUILT_IN_STRNCPY:
 	case BUILT_IN_MEMSET:
 	case BUILT_IN_MEMCPY_CHK:
 	case BUILT_IN_MEMMOVE_CHK:
+	case BUILT_IN_STRNCPY_CHK:
 	case BUILT_IN_MEMSET_CHK:
 	  {
 	    /* Occasionally calls with an explicit length of zero