[gcc/devel/c++-coroutines] c: Handle MEM_REF in c_fully_fold* [PR94179]

[gcc/devel/c++-coroutines] c: Handle MEM_REF in c_fully_fold* [PR94179]

[Iain D Sandoe]

https://gcc.gnu.org/g:c015ff8ccaf3ee8e4f6393679ed790ed0df92873

commit c015ff8ccaf3ee8e4f6393679ed790ed0df92873
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Mon Mar 16 22:58:41 2020 +0100

    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:
---
 gcc/c/ChangeLog                               | 5 +++++
 gcc/c/c-fold.c                                | 9 +++++++++
 gcc/testsuite/ChangeLog                       | 5 +++++
 gcc/testsuite/gcc.c-torture/compile/pr94179.c | 9 +++++++++
 4 files changed, 28 insertions(+)

diff --git a/gcc/c/ChangeLog b/gcc/c/ChangeLog
index d3a3b2fc784..240859e9fed 100644
--- 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 fde2d55e579..63becfeaf2c 100644
--- 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 3b277cecac3..f0d703369a8 100644
--- 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
index 00000000000..dfe27fe61d4
--- /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);
+}