[PATCH] Fix PR83128

[Richard Biener]

We somehow forgot to handle STRING_CSTs when looking through memcpy
like functions.

Fixed as follows, bootstrapped and tested on x86_64-unknown-linux-gnu, 
applied.

Richard.

2017-11-24  Richard Biener  <rguent...@suse.de>

        PR tree-optimization/83128
        * tree-ssa-sccvn.c (fully_constant_vn_reference_p): Handle STRING_CSTs.
        (vn_reference_lookup_3): Likewise.

        * gcc.dg/tree-ssa/ssa-fre-62.c: New testcase.

Index: gcc/tree-ssa-sccvn.c
===================================================================
--- gcc/tree-ssa-sccvn.c        (revision 255093)
+++ gcc/tree-ssa-sccvn.c        (working copy)
@@ -1388,10 +1388,14 @@ fully_constant_vn_reference_p (vn_refere
       else if (base->opcode == MEM_REF
               && base[1].opcode == ADDR_EXPR
               && (TREE_CODE (TREE_OPERAND (base[1].op0, 0)) == VAR_DECL
-                  || TREE_CODE (TREE_OPERAND (base[1].op0, 0)) == CONST_DECL))
+                  || TREE_CODE (TREE_OPERAND (base[1].op0, 0)) == CONST_DECL
+                  || TREE_CODE (TREE_OPERAND (base[1].op0, 0)) == STRING_CST))
        {
          decl = TREE_OPERAND (base[1].op0, 0);
-         ctor = ctor_for_folding (decl);
+         if (TREE_CODE (decl) == STRING_CST)
+           ctor = decl;
+         else
+           ctor = ctor_for_folding (decl);
        }
       if (ctor == NULL_TREE)
        return build_zero_cst (ref->type);
@@ -2331,7 +2335,8 @@ vn_reference_lookup_3 (ao_ref *ref, tree
              rhs = TREE_OPERAND (tem, 0);
              rhs_offset += tree_to_uhwi (TREE_OPERAND (tem, 1));
            }
-         else if (DECL_P (tem))
+         else if (DECL_P (tem)
+                  || TREE_CODE (tem) == STRING_CST)
            rhs = build_fold_addr_expr (tem);
          else
            return (void *)-1;
Index: gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-62.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-62.c  (nonexistent)
+++ gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-62.c  (working copy)
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-fre1" } */
+
+char f()
+{
+  char *i = (char*)__builtin_malloc(100);
+  __builtin_memcpy(i, "a", 1);
+  return i[0];
+}
+
+/* { dg-final { scan-tree-dump "return 97;" "fre1" } } */