Hi!
The recent match.pd changes can generate a MEM_REF which can be seen by the
C FE folding routines. Unlike the C++ FE, they weren't expected in the C FE
yet. MEM_REF should be handled like INDIRECT_REF, except that it has two
operands rather than just one and that we should preserve the type of the
second operand. Given that it already has to be an INTEGER_CST with pointer
type, I think we are fine, the recursive call should return the INTEGER_CST
unmodified and STRIP_TYPE_NOPS will not strip anything.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2020-03-16 Jakub Jelinek <ja...@redhat.com>
PR c/94179
* c-fold.c (c_fully_fold_internal): Handle MEM_REF.
* gcc.c-torture/compile/pr94179.c: New test.
--- gcc/c/c-fold.c.jj 2020-01-12 11:54:36.208416501 +0100
+++ gcc/c/c-fold.c 2020-03-15 17:26:42.863491563 +0100
@@ -346,6 +346,7 @@ c_fully_fold_internal (tree expr, bool i
case UNGT_EXPR:
case UNGE_EXPR:
case UNEQ_EXPR:
+ case MEM_REF:
/* Binary operations evaluating both arguments (increment and
decrement are binary internally in GCC). */
orig_op0 = op0 = TREE_OPERAND (expr, 0);
@@ -435,6 +436,14 @@ c_fully_fold_internal (tree expr, bool i
|| TREE_CODE (TREE_TYPE (orig_op0)) == FIXED_POINT_TYPE)
&& TREE_CODE (TREE_TYPE (orig_op1)) == INTEGER_TYPE)
warn_for_div_by_zero (loc, op1);
+ if (code == MEM_REF
+ && ret != expr
+ && TREE_CODE (ret) == MEM_REF)
+ {
+ TREE_READONLY (ret) = TREE_READONLY (expr);
+ TREE_SIDE_EFFECTS (ret) = TREE_SIDE_EFFECTS (expr);
+ TREE_THIS_VOLATILE (ret) = TREE_THIS_VOLATILE (expr);
+ }
goto out;
case ADDR_EXPR:
--- gcc/testsuite/gcc.c-torture/compile/pr94179.c.jj 2020-03-15
17:14:20.782511288 +0100
+++ gcc/testsuite/gcc.c-torture/compile/pr94179.c 2020-03-15
17:13:48.913984847 +0100
@@ -0,0 +1,9 @@
+/* PR c/94179 */
+
+struct S { char c, d, e[64]; } a;
+
+unsigned char *
+foo (int b)
+{
+ return (unsigned char *)((char *)&a.e[b != 0] - (char *)&((struct S *)0)->d);
+}
Jakub
