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