diff mbox

match.pd: reassociate multiplications with constants

Message ID alpine.LNX.2.20.13.1707151944240.20069@monopod.intra.ispras.ru
State New
Headers show

Commit Message

Alexander Monakov July 15, 2017, 5 p.m. UTC 
On Thu, 13 Jul 2017, Marc Glisse wrote:
> I notice that we do not turn (X*10)*10 into X*100 in GIMPLE [...]

I've completely missed that.  Posting another patch to address that.

> Relying on inner expressions being folded can be slightly dangerous,
> especially for generic IIRC. It seems easy enough to check that @1 is neither
> 0 nor -1 for safety.

Yep - done.

> Probably needs :s on the inner multiplication.

Not 100% sure, but done in this version.

> Unless the test on TYPE_OVERFLOW_SANITIZED etc is shared with adjacent
> transformations, I'd rather put it inside, with the other if, but that's a
> matter of taste.

Done, probably better that way.
 
> One small testcase please? Or is there already one that is currently failing?

No, I'm not aware of any preexisting testcase.  Added.

	* match.pd ((X * CST) * Y): Reassociate to (X * Y) * CST.
testsuite/
	* gcc.dg/tree-ssa/assoc-2.c: New testcase.
diff mbox

Patch

diff --git a/gcc/match.pd b/gcc/match.pd
index 4c64b21..36045f1 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -2139,6 +2139,15 @@  DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
  (mult @0 integer_minus_onep)
  (negate @0))
 
+/* Reassociate (X * CST) * Y to (X * Y) * CST.  This does not introduce
+   signed overflow for CST != 0 && CST != -1.  */
+(simplify
+ (mult:c (mult:s @0 INTEGER_CST@1) @2)
+ (if (TREE_CODE (@2) != INTEGER_CST
+      && !integer_zerop (@1) && !integer_minus_onep (@1)
+      && !TYPE_OVERFLOW_SANITIZED (type) && !TYPE_SATURATING (type))
+  (mult (mult @0 @2) @1)))
+
 /* True if we can easily extract the real and imaginary parts of a complex
    number.  */
 (match compositional_complex
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/assoc-2.c b/gcc/testsuite/gcc.dg/tree-ssa/assoc-2.c
new file mode 100644
index 0000000..a92c882
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/assoc-2.c
@@ -0,0 +1,8 @@ 
+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-gimple-raw -fdump-tree-optimized-raw" } */
+
+int f0(int a, int b){
+  return a * 33 * b * 55;
+}
+
+/* { dg-final { scan-tree-dump-times "mult_expr" 2 "gimple" } } */