[C PATCH] Don't leak C_MAYBE_CONST_EXPRs into GIMPLE (PR c/59891)

[Marek Polacek]

As mentioned in the PR, C FE leaked C_MAYBE_CONST_EXPR into GIMPLE.
This happened because remove_c_maybe_const_expr doesn't look for
nested C_MAYBE_CONST_EXPRs.  But c_fully_fold will fold these away,
so use that.

Regtested/bootstrapped on x86_64-linux, ok for trunk and 4.8?

Alternatively, we could in if (int_operands) look at op1/op2, and
call c_fully_fold only if C_MAYBE_CONST_EXPR isn't the top level
expression.

2014-01-22  Marek Polacek  <pola...@redhat.com>

        PR c/59891
c/
        * c-typeck.c (build_conditional_expr): Call c_fully_fold instead
        of remove_c_maybe_const_expr on op1 and op2.
testsuite/
        * gcc.dg/torture/pr59891.c: New test.

--- gcc/c/c-typeck.c.mp3        2014-01-22 18:47:36.812358319 +0100
+++ gcc/c/c-typeck.c    2014-01-22 18:45:10.298692933 +0100
@@ -4708,8 +4708,10 @@ build_conditional_expr (location_t colon
     {
       if (int_operands)
        {
-         op1 = remove_c_maybe_const_expr (op1);
-         op2 = remove_c_maybe_const_expr (op2);
+         /* Use c_fully_fold here, since C_MAYBE_CONST_EXPR might be
+            nested inside of the expression.  */
+         op1 = c_fully_fold (op1, false, NULL);
+         op2 = c_fully_fold (op2, false, NULL);
        }
       ret = build3 (COND_EXPR, result_type, ifexp, op1, op2);
       if (int_operands)
--- gcc/testsuite/gcc.dg/torture/pr59891.c.mp3  2014-01-22 19:16:34.000000000 
+0100
+++ gcc/testsuite/gcc.dg/torture/pr59891.c      2014-01-22 19:19:23.996129684 
+0100
@@ -0,0 +1,9 @@
+/* PR c/59891 */
+
+unsigned int a;
+
+int
+main ()
+{
+  return (0 ? a : 0) ? : 0 % 0; /* { dg-warning "division by zero" } */
+}

        Marek