c: Handle MEM_REF in c_fully_fold* [PR94179]

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.

2020-03-16  Jakub Jelinek  <jakub@redhat.com>

	PR c/94179
	* c-fold.c (c_fully_fold_internal): Handle MEM_REF.

	* gcc.c-torture/compile/pr94179.c: New test.

diff --git a/gcc/c/ChangeLog b/gcc/c/ChangeLog
index d3a3b2fc78412e205e0d5d769411e8a112c33f50..240859e9fedf1e79f787df2feaf03d80ece7d5be 100644 (file)
--- a/gcc/c/ChangeLog
+++ b/gcc/c/ChangeLog
@@ -1,3 +1,8 @@
+2020-03-16  Jakub Jelinek  <jakub@redhat.com>
+
+       PR c/94179
+       * c-fold.c (c_fully_fold_internal): Handle MEM_REF.
+
 2020-03-13  Martin Sebor  <msebor@redhat.com>
 
        PR c/94040

diff --git a/gcc/c/c-fold.c b/gcc/c/c-fold.c
index fde2d55e579e7e548bceba350138d0750ddad69d..63becfeaf2c1535fa3dd49c12519b941bed5dc71 100644 (file)
--- a/gcc/c/c-fold.c
+++ b/gcc/c/c-fold.c
@@ -346,6 +346,7 @@ c_fully_fold_internal (tree expr, bool in_init, bool *maybe_const_operands,
     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 in_init, bool *maybe_const_operands,
              || 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:

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 3b277cecac3b222602054530449c374625d99fec..f0d703369a8188711e99fbac72622ae1f343c316 100644 (file)
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2020-03-16  Jakub Jelinek  <jakub@redhat.com>
+
+       PR c/94179
+       * gcc.c-torture/compile/pr94179.c: New test.
+
 2020-03-16  Vladimir Makarov  <vmakarov@redhat.com>
 
        PR target/94185

diff --git a/gcc/testsuite/gcc.c-torture/compile/pr94179.c b/gcc/testsuite/gcc.c-torture/compile/pr94179.c
new file mode 100644 (file)
index 0000000..dfe27fe
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/compile/pr94179.c
@@ -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);
+}