[(8/7)] Fix a bug in multiply-and-accumulate

Submitted by Andrew Stubbs on July 21, 2011, 1:14 p.m.

Details

Message ID 4E28262F.4080503@codesourcery.com
State New
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Commit Message

Andrew Stubbs July 21, 2011, 1:14 p.m.
On 18/07/11 15:46, Richard Guenther wrote:
> Will signedness be always the same?  Usually the canonical check to
> use would be !useless_type_conversion_p (type, TREE_TYPE (add_rhs)).

The signedness ought to be unimportant - any extend will be based on the 
source type, and the signedness should not affect the addition 
operation. That said, it really ought to remain correct or else bad 
things could happen in later optimizations ....

Here is the patch I plan to commit, when patch 1 is approved, and my 
testing is complete.

Andrew

Comments

Andrew Stubbs Aug. 19, 2011, 3:02 p.m.
On 21/07/11 14:14, Andrew Stubbs wrote:
> Here is the patch I plan to commit, when patch 1 is approved, and my
> testing is complete.

Committed, unchanged.

Andrew

Patch hide | download patch | download mbox

2011-07-21  Andrew Stubbs  <ams@codesourcery.com>

	gcc/
	* tree-ssa-math-opts.c (convert_plusminus_to_widen): Convert add_rhs
	to the correct type.

	gcc/testsuite/
	* gcc.target/arm/wmul-10.c: New file.

--- /dev/null
+++ b/gcc/testsuite/gcc.target/arm/wmul-10.c
@@ -0,0 +1,12 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+/* { dg-require-effective-target arm_dsp } */
+
+
+unsigned long long
+foo (unsigned short a, unsigned short *b, unsigned short *c)
+{
+  return (unsigned)a + (unsigned long long)*b * (unsigned long long)*c;
+}
+
+/* { dg-final { scan-assembler "umlal" } } */
--- a/gcc/tree-ssa-math-opts.c
+++ b/gcc/tree-ssa-math-opts.c
@@ -2375,6 +2375,10 @@  convert_plusminus_to_widen (gimple_stmt_iterator *gsi, gimple stmt,
       mult_rhs2 = build_and_insert_cast (gsi, loc, tmp, mult_rhs2);
     }
 
+  if (!useless_type_conversion_p (type, TREE_TYPE (add_rhs)))
+    add_rhs = build_and_insert_cast (gsi, loc, create_tmp_var (type, NULL),
+				     add_rhs);
+
   gimple_assign_set_rhs_with_ops_1 (gsi, wmult_code, mult_rhs1, mult_rhs2,
 				    add_rhs);
   update_stmt (gsi_stmt (*gsi));