PR tree-optimization/87028 - false positive -Wstringop-truncation strncpy with global variable source string

gcc/ChangeLog:

	PR tree-optimization/87028
	* calls.c (get_attr_nonstring_decl): Avoid setting *REF to
	SSA_NAME_VAR.
	* gcc/gimple-low.c (lower_stmt): Delay foldin built-ins.
	* gimplify (maybe_fold_stmt): Avoid folding statements that
	don't belong to a basic block.
	* tree.h (SSA_NAME_VAR): Update comment.
	* tree-ssa-strlen.c (maybe_diag_stxncpy_trunc): Simplify.

gcc/testsuite/ChangeLog:

	PR tree-optimization/87028
	* c-c++-common/Wstringop-truncation.c: Remove xfails.
	* gcc.dg/Wstringop-truncation-5.c: New test.
	* gcc.dg/strcmpopt_1.c: Adjust.
	* gcc.dg/tree-ssa/pr79697.c: Same.

Index: gcc/calls.c
===================================================================
--- gcc/calls.c	(revision 266637)
+++ gcc/calls.c	(working copy)
@@ -1503,6 +1503,7 @@ tree
 get_attr_nonstring_decl (tree expr, tree *ref)
 {
   tree decl = expr;
+  tree var = NULL_TREE;
   if (TREE_CODE (decl) == SSA_NAME)
     {
       gimple *def = SSA_NAME_DEF_STMT (decl);
@@ -1515,17 +1516,25 @@ get_attr_nonstring_decl (tree expr, tree *ref)
 	      || code == VAR_DECL)
 	    decl = gimple_assign_rhs1 (def);
 	}
-      else if (tree var = SSA_NAME_VAR (decl))
-	decl = var;
+      else
+	var = SSA_NAME_VAR (decl);
     }
 
   if (TREE_CODE (decl) == ADDR_EXPR)
     decl = TREE_OPERAND (decl, 0);
 
+  /* To simplify calling code, store the referenced DECL regardless of
+     the attribute determined below, but avoid storing the SSA_NAME_VAR
+     obtained above (it's not useful for dataflow purposes).  */
   if (ref)
     *ref = decl;
 
-  if (TREE_CODE (decl) == ARRAY_REF)
+  /* Use the SSA_NAME_VAR that was determined above to see if it's
+     declared nonstring.  Otherwise drill down into the referenced
+     DECL.  */
+  if (var)
+    decl = var;
+  else if (TREE_CODE (decl) == ARRAY_REF)
     decl = TREE_OPERAND (decl, 0);
   else if (TREE_CODE (decl) == COMPONENT_REF)
     decl = TREE_OPERAND (decl, 1);
Index: gcc/gimple-low.c
===================================================================
--- gcc/gimple-low.c	(revision 266637)
+++ gcc/gimple-low.c	(working copy)
@@ -32,6 +32,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "gimple-low.h"
 #include "predict.h"
 #include "gimple-predict.h"
+#include "gimple-fold.h"
 
 /* The differences between High GIMPLE and Low GIMPLE are the
    following:
@@ -378,6 +379,12 @@ lower_stmt (gimple_stmt_iterator *gsi, struct lowe
 	    gsi_next (gsi);
 	    return;
 	  }
+
+	/* We delay folding of built calls from gimplification to
+	   here so the IL is in consistent state for the diagnostic
+	   machineries job.  */
+	if (gimple_call_builtin_p (stmt))
+	  fold_stmt (gsi);
       }
       break;
 
Index: gcc/gimplify.c
===================================================================
--- gcc/gimplify.c	(revision 266637)
+++ gcc/gimplify.c	(working copy)
@@ -3192,6 +3192,10 @@ maybe_fold_stmt (gimple_stmt_iterator *gsi)
       return false;
     else if ((ctx->region_type & ORT_HOST_TEAMS) == ORT_HOST_TEAMS)
       return false;
+  /* Delay folding of builtins until the IL is in consistent state
+     so the diagnostic machinery can do a better job.  */
+  if (gimple_call_builtin_p (gsi_stmt (*gsi)))
+    return false;
   return fold_stmt (gsi);
 }
 
Index: gcc/testsuite/c-c++-common/Wstringop-truncation.c
===================================================================
--- gcc/testsuite/c-c++-common/Wstringop-truncation.c	(revision 266637)
+++ gcc/testsuite/c-c++-common/Wstringop-truncation.c	(working copy)
@@ -329,9 +329,8 @@ void test_strncpy_array (Dest *pd, int i, const ch
      of the array to NUL is not diagnosed.  */
   {
     /* This might be better written using memcpy() but it's safe so
-       it probably shouldn't be diagnosed.  It currently triggers
-       a warning because of bug 81704.  */
-    strncpy (dst7, "0123456", sizeof dst7);   /* { dg-bogus "\\\[-Wstringop-truncation]" "bug 81704" { xfail *-*-* } } */
+       it shouldn't be diagnosed.  */
+    strncpy (dst7, "0123456", sizeof dst7);   /* { dg-bogus "\\\[-Wstringop-truncation]" } */
     dst7[sizeof dst7 - 1] = '\0';
     sink (dst7);
   }
@@ -350,7 +349,7 @@ void test_strncpy_array (Dest *pd, int i, const ch
   }
 
   {
-    strncpy (pd->a5, "01234", sizeof pd->a5);   /* { dg-bogus "\\\[-Wstringop-truncation]" "bug 81704" { xfail *-*-* } } */
+    strncpy (pd->a5, "01234", sizeof pd->a5);   /* { dg-bogus "\\\[-Wstringop-truncation]" } */
     pd->a5[sizeof pd->a5 - 1] = '\0';
     sink (pd);
   }
Index: gcc/testsuite/gcc.dg/Wstringop-truncation-5.c
===================================================================
--- gcc/testsuite/gcc.dg/Wstringop-truncation-5.c	(nonexistent)
+++ gcc/testsuite/gcc.dg/Wstringop-truncation-5.c	(working copy)
@@ -0,0 +1,64 @@
+/* PR tree-optimization/87028 - false positive -Wstringop-truncation
+   strncpy with global variable source string
+   { dg-do compile }
+   { dg-options "-O2 -Wstringop-truncation" } */
+
+char *strncpy (char *, const char *, __SIZE_TYPE__);
+
+#define STR   "1234567890"
+
+struct S
+{
+  char a[5], b[5];
+};
+
+const char arr[] = STR;
+const char* const ptr = STR;
+
+const char arr2[][10] = { "123", STR };
+
+void test_literal (struct S *s)
+{
+  strncpy (s->a, STR, sizeof s->a - 1);     /* { dg-bogus "\\\[-Wstringop-truncation]" } */
+  s->a[sizeof s->a - 1] = '\0';
+}
+
+void test_global_arr (struct S *s)
+{
+  strncpy (s->a, arr, sizeof s->a - 1);     /* { dg-bogus "\\\[-Wstringop-truncation]" } */
+  s->a [sizeof s->a - 1] = '\0';
+}
+
+void test_global_arr2 (struct S *s)
+{
+  strncpy (s->a, arr2[1], sizeof s->a - 1); /* { dg-bogus "\\\[-Wstringop-truncation]" } */
+  s->a [sizeof s->a - 1] = '\0';
+
+  strncpy (s->b, arr2[0], sizeof s->a - 1);
+}
+
+void test_global_ptr (struct S *s)
+{
+  strncpy (s->a, ptr, sizeof s->a - 1);     /* { dg-bogus "\\\[-Wstringop-truncation]" } */
+  s->a [sizeof s->a - 1] = '\0';
+}
+
+void test_local_arr (struct S *s)
+{
+  const char arr[] = STR;
+  strncpy (s->a, arr, sizeof s->a - 1);
+  s->a [sizeof s->a - 1] = '\0';
+}
+
+void test_local_ptr (struct S *s)
+{
+  const char* const ptr = STR;
+  strncpy (s->a, ptr, sizeof s->a - 1);     /* { dg-bogus "\\\[-Wstringop-truncation]" } */
+  s->a [sizeof s->a - 1] = '\0';
+}
+
+void test_compound_literal (struct S *s)
+{
+  strncpy (s->a, (char[]){ STR }, sizeof s->a - 1);
+  s->a [sizeof s->a - 1] = '\0';
+}
Index: gcc/testsuite/gcc.dg/fold-bcopy.c
===================================================================
--- gcc/testsuite/gcc.dg/fold-bcopy.c	(revision 266637)
+++ gcc/testsuite/gcc.dg/fold-bcopy.c	(working copy)
@@ -1,6 +1,6 @@
 /* PR tree-optimization/80933 - redundant bzero/bcopy calls not eliminated
    { dg-do compile }
-   { dg-options "-O0 -Wall -fdump-tree-gimple" } */
+   { dg-options "-O1 -Wall -fdump-tree-lower" } */
 
 void f0 (void *dst, const void *src, unsigned n)
 {
@@ -46,9 +46,9 @@ void f6 (void *p)
 /* Verify that calls to bcmp, bcopy, and bzero have all been removed
    and one of each replaced with memcmp, memmove, and memset, respectively.
    The remaining three should be eliminated.
-  { dg-final { scan-tree-dump-not "bcmp|bcopy|bzero" "gimple" } }
-  { dg-final { scan-tree-dump-times "memcmp|memmove|memset" 3 "gimple" } }
+  { dg-final { scan-tree-dump-not "bcmp|bcopy|bzero" "lower" } }
+  { dg-final { scan-tree-dump-times "memcmp|memmove|memset" 3 "lower" } }
 
   Verify that the bcopy to memmove transformation correctly transposed
   the source and destination pointer arguments.
-  { dg-final { scan-tree-dump-times "memmove \\(dst, src" 1 "gimple" } }  */
+  { dg-final { scan-tree-dump-times "memmove \\(dst, src" 1 "lower" } }  */
Index: gcc/testsuite/gcc.dg/strcmpopt_1.c
===================================================================
--- gcc/testsuite/gcc.dg/strcmpopt_1.c	(revision 266637)
+++ gcc/testsuite/gcc.dg/strcmpopt_1.c	(working copy)
@@ -1,5 +1,5 @@
 /* { dg-do run } */
-/* { dg-options "-fdump-tree-gimple" } */
+/* { dg-options "-fdump-tree-lower" } */
 
 #include <string.h>
 #include <stdlib.h>
@@ -25,4 +25,4 @@ int main ()
   return 0;
 }
 
-/* { dg-final { scan-tree-dump-times "strcmp \\(" 2 "gimple" } } */
+/* { dg-final { scan-tree-dump-times "strcmp \\(" 2 "lower" } } */
Index: gcc/testsuite/gcc.dg/tree-ssa/pr79697.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/pr79697.c	(revision 266637)
+++ gcc/testsuite/gcc.dg/tree-ssa/pr79697.c	(working copy)
@@ -1,5 +1,5 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -fdump-tree-gimple -fdump-tree-cddce-details -fdump-tree-optimized" } */
+/* { dg-options "-O2 -fdump-tree-lower -fdump-tree-cddce-details -fdump-tree-optimized" } */
 
 void f(void)
 {
@@ -18,4 +18,4 @@ void h(void)
 
 /* { dg-final { scan-tree-dump "Deleting : __builtin_strdup" "cddce1" } } */
 /* { dg-final { scan-tree-dump "Deleting : __builtin_strndup" "cddce1" } } */
-/* { dg-final { scan-tree-dump "__builtin_malloc" "gimple" } } */
+/* { dg-final { scan-tree-dump "__builtin_malloc" "lower" } } */