Re: Fix PR57886, invalid folding of conversion

[Michael Matz <matz at suse dot de>]

Hi,

On Fri, 12 Jul 2013, Michael Matz wrote:

> Hi,
> 
> GCC happily transforms (float)-z into -(float)z, even when z is of 
> unsigned type (when it's larger than float).  That's wrong (the result 
> should always be positive, because -z is).  It seems to me that this bug 
> exists in all reasonably recent GCC versions.  The checking in 
> convert_to_real is wrong, it compares type precisions of different 
> classed types.  The change with the least impact is to reject only 
> TYPE_UNSIGNED inner types, but perhaps it would be better to only do the 
> transformation if the inner type is FLOAT_TYPE_P as well.

So, this is a dup of PR55771, I'm now proposing to add a test for 
FLOAT_TYPE_P, not TYPE_UNSIGNED.  Restarted the regstrap.


Ciao,
Michael.
-- 
	PR middle-end/55771
	* convert.c (convert_to_real): Reject non-float inner types.

testsuite/
	* c-c++-common/pr55771.c: New test.

Index: convert.c
===================================================================
--- convert.c	(revision 200240)
+++ convert.c	(working copy)
@@ -213,10 +213,11 @@ convert_to_real (tree type, tree expr)
     switch (TREE_CODE (expr))
       {
 	/* Convert (float)-x into -(float)x.  This is safe for
-	   round-to-nearest rounding mode.  */
+	   round-to-nearest rounding mode when the inner type is float.  */
 	case ABS_EXPR:
 	case NEGATE_EXPR:
 	  if (!flag_rounding_math
+	      && FLOAT_TYPE_P (itype)
 	      && TYPE_PRECISION (type) < TYPE_PRECISION (TREE_TYPE (expr)))
 	    return build1 (TREE_CODE (expr), type,
 			   fold (convert_to_real (type,
Index: testsuite/c-c++-common/pr55771.c
===================================================================
--- testsuite/c-c++-common/pr55771.c	(revision 0)
+++ testsuite/c-c++-common/pr55771.c	(working copy)
@@ -0,0 +1,12 @@
+/* { dg-do run } */
+
+float global;
+int main()
+{
+  unsigned long z = 1;
+  float x = -z;
+  global = x;
+  if (global < 0)
+    __builtin_abort ();
+  return 0;
+}