Re: C++ PATCH to fix ICE with bit-fields and ?: (PR c++/81607)

[Jason Merrill]

OK.

C++ PATCH to fix ICE with bit-fields and ?: (PR c++/81607)

[Marek Polacek]

We crash in the gimplifier because it sees a shift expression with different
types of op1/op2.  The problem arises in cp_fold: it gets "1 ? d.c : 0" of type
int which is folded to "d.c", but it then sees that d.c is a bit-field with
declared type long int, so if produces "(long int) d.c" -- but that differs
from the original COND_EXPR type!  Folding should not change the type of the
CODE_EXPR, thus this fix.

Bootstrapped/regtested on x86_64-linux, ok for trunk/7/6?

2017-07-31  Marek Polacek  

PR c++/81607
* cp-gimplify.c (cp_fold): If folding exposed a branch of
a COND_EXPR, convert it to the original type of the COND_EXPR, if
they differ.   

* g++.dg/other/bitfield6.C: New test.

diff --git gcc/cp/cp-gimplify.c gcc/cp/cp-gimplify.c
index a9563b1a8cd..9fc4ab18207 100644
--- gcc/cp/cp-gimplify.c
+++ gcc/cp/cp-gimplify.c
@@ -2314,9 +2314,9 @@ cp_fold (tree x)
 
   /* A COND_EXPR might have incompatible types in branches if one or both
 arms are bitfields.  If folding exposed such a branch, fix it up.  */
-  if (TREE_CODE (x) != code)
-   if (tree type = is_bitfield_expr_with_lowered_type (x))
- x = fold_convert (type, x);
+  if (TREE_CODE (x) != code
+ && !useless_type_conversion_p (TREE_TYPE (org_x), TREE_TYPE (x)))
+   x = fold_convert (TREE_TYPE (org_x), x);
 
   break;
 
diff --git gcc/testsuite/g++.dg/other/bitfield6.C 
gcc/testsuite/g++.dg/other/bitfield6.C
index e69de29bb2d..c1e8a17989b 100644
--- gcc/testsuite/g++.dg/other/bitfield6.C
+++ gcc/testsuite/g++.dg/other/bitfield6.C
@@ -0,0 +1,9 @@
+// PR c++/81607
+
+int a;
+
+struct b {
+  long c : 32;
+} d;
+
+char f = (903092 ? int(d.c) : 0) << a;

Marek