diff mbox

Relax VIEW_CONVERT_EXPR - CONVERT_EXPR combination

Message ID alpine.DEB.2.02.1705212313230.2140@stedding.saclay.inria.fr
State New
Headers show

Commit Message

Marc Glisse May 21, 2017, 9:21 p.m. UTC 
Hello,

SRA uses char when scalarizing bool, and we end up with

   _6 = u_1(D) == 0.0;
   _7 = (unsigned char) _6;
   _3 = VIEW_CONVERT_EXPR<_Bool>(_7);

which we currently do not simplify. I am not completely sure what happens 
with types whose precision does not cover their size, I hope this is safe.

Bootstrap+testsuite on powerpc64le-unknown-linux-gnu.

2017-05-22  Marc Glisse  <marc.glisse@inria.fr>

gcc/
 	* match.pd (view_convert (convert@0 @1)): Handle zero-extension.

gcc/testsuite/
 	* gcc.dg/tree-ssa/vce-1.c: New file.

Comments

Richard Biener May 24, 2017, 8:57 a.m. UTC | #1 
On Sun, May 21, 2017 at 11:21 PM, Marc Glisse <marc.glisse@inria.fr> wrote:
> Hello,
>
> SRA uses char when scalarizing bool, and we end up with
>
>   _6 = u_1(D) == 0.0;
>   _7 = (unsigned char) _6;
>   _3 = VIEW_CONVERT_EXPR<_Bool>(_7);
>
> which we currently do not simplify. I am not completely sure what happens
> with types whose precision does not cover their size, I hope this is safe.

Hmm, if zero-extension is safe so should sign-extension, no?  Because
if size != precision then both can actually change bits outside of the
precision?

I realize zero-extension is "safer" in some sense as the extended value
is the same for all precisions.

Thus OK.

thanks,
Richard.

> Bootstrap+testsuite on powerpc64le-unknown-linux-gnu.
>
> 2017-05-22  Marc Glisse  <marc.glisse@inria.fr>
>
> gcc/
>         * match.pd (view_convert (convert@0 @1)): Handle zero-extension.
>
> gcc/testsuite/
>         * gcc.dg/tree-ssa/vce-1.c: New file.
>
> --
> Marc Glisse
diff mbox

Patch

Index: match.pd
===================================================================
--- match.pd	(revision 248312)
+++ match.pd	(working copy)
@@ -1798,27 +1798,30 @@  DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
 
 /* For integral conversions with the same precision or pointer
    conversions use a NOP_EXPR instead.  */
 (simplify
   (view_convert @0)
   (if ((INTEGRAL_TYPE_P (type) || POINTER_TYPE_P (type))
        && (INTEGRAL_TYPE_P (TREE_TYPE (@0)) || POINTER_TYPE_P (TREE_TYPE (@0)))
        && TYPE_PRECISION (type) == TYPE_PRECISION (TREE_TYPE (@0)))
    (convert @0)))
 
-/* Strip inner integral conversions that do not change precision or size.  */
+/* Strip inner integral conversions that do not change precision or size, or
+   zero-extend while keeping the same size (for bool-to-char).  */
 (simplify
   (view_convert (convert@0 @1))
   (if ((INTEGRAL_TYPE_P (TREE_TYPE (@0)) || POINTER_TYPE_P (TREE_TYPE (@0)))
        && (INTEGRAL_TYPE_P (TREE_TYPE (@1)) || POINTER_TYPE_P (TREE_TYPE (@1)))
-       && (TYPE_PRECISION (TREE_TYPE (@0)) == TYPE_PRECISION (TREE_TYPE (@1)))
-       && (TYPE_SIZE (TREE_TYPE (@0)) == TYPE_SIZE (TREE_TYPE (@1))))
+       && TYPE_SIZE (TREE_TYPE (@0)) == TYPE_SIZE (TREE_TYPE (@1))
+       && (TYPE_PRECISION (TREE_TYPE (@0)) == TYPE_PRECISION (TREE_TYPE (@1))
+	   || (TYPE_PRECISION (TREE_TYPE (@0)) > TYPE_PRECISION (TREE_TYPE (@1))
+	       && TYPE_UNSIGNED (TREE_TYPE (@1)))))
    (view_convert @1)))
 
 /* Re-association barriers around constants and other re-association
    barriers can be removed.  */
 (simplify
  (paren CONSTANT_CLASS_P@0)
  @0)
 (simplify
  (paren (paren@1 @0))
  @1)
Index: testsuite/gcc.dg/tree-ssa/vce-1.c
===================================================================
--- testsuite/gcc.dg/tree-ssa/vce-1.c	(nonexistent)
+++ testsuite/gcc.dg/tree-ssa/vce-1.c	(working copy)
@@ -0,0 +1,14 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+typedef struct { _Bool b; } A;
+_Bool f(double u){
+  A a;
+  if(u==0)
+    a.b=1;
+  else
+    a.b=0;
+  return a.b;
+}
+
+/* { dg-final { scan-tree-dump-not "VIEW_CONVERT_EXPR" "optimized" } } */