Previous revision here: https://gcc.gnu.org/ml/gcc-patches/2017-07/msg00889.html
Reassociate (X * CST) * Y to (X * Y) * CST, this pushes constants in
multiplication chains to outermost factors, where they can be combined.
Changed in this revision:
- remove !TYPE_OVERFLOW_SANITIZED and !TYPE_SATURATING checks;
(in previous discussion Richard indicated that introducing false negatives
in UBSAN by concealing signed overflow is not a concern, and saturating
types shouldn't appear here because the constant operand should be FIXED_CST)
The checks for @1 being 0 or -1 remain as they are required for correctness,
but since this rule is ordered after the simpler rules that fold X * {0, -1},
those checks are always false at runtime.
* match.pd ((X * CST) * Y): Reassociate to (X * Y) * CST.
testsuite/
* gcc.dg/tree-ssa/assoc-2.c: New testcase.
---
gcc/match.pd | 8 ++++++++
gcc/testsuite/gcc.dg/tree-ssa/assoc-2.c | 8 ++++++++
2 files changed, 16 insertions(+)
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/assoc-2.c
diff --git a/gcc/match.pd b/gcc/match.pd
index 7f5807c..39e1e5c 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -2213,6 +2213,14 @@ 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))
+ (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" } } */
--
1.8.3.1
