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| author | Roger Sayle <roger@nextmovesoftware.com> | 2022-08-15 17:39:47 +0100 |
|---|---|---|
| committer | Roger Sayle <roger@nextmovesoftware.com> | 2022-08-15 17:39:47 +0100 |
| commit | 418b71c0d535bf91df78bad2e198c57934682eaa (patch) | |
| tree | 16091b0ba4b39cef0024221c90b938a31b1c0939 | |
| parent | 03acd8b6429e22068330dce5abf129291d3f26de (diff) | |
| download | gcc-418b71c0d535bf91df78bad2e198c57934682eaa.zip gcc-418b71c0d535bf91df78bad2e198c57934682eaa.tar.gz gcc-418b71c0d535bf91df78bad2e198c57934682eaa.tar.bz2 | |
PR tree-optimization/64992: (B << 2) != 0 is B when B is Boolean.
This patch resolves both PR tree-optimization/64992 and PR
tree-optimization/98956 which are missed optimization enhancement
request, for which Andrew Pinski already has a proposed solution
(related to a fix for PR tree-optimization/98954). Yesterday,
I proposed an alternate improved patch for PR98954, which although
superior in most respects, alas didn't address this case [which
doesn't include a BIT_AND_EXPR], hence this follow-up fix.
For many functions, F(B), of a (zero-one) Boolean value B, the
expression F(B) != 0 can often be simplified to just B. Hence
"(B * 5) != 0" is B, "-B != 0" is B, "bswap(B) != 0" is B,
"(B >>r 3) != 0" is B. These are all currently optimized by GCC,
with the strange exception of left shifts by a constant (possibly
due to the undefined/implementation defined behaviour when the
shift constant is larger than the first operand's precision).
This patch adds support for this particular case, when the shift
constant is valid.
2022-08-15 Roger Sayle <roger@nextmovesoftware.com>
gcc/ChangeLog
PR tree-optimization/64992
PR tree-optimization/98956
* match.pd (ne (lshift @0 @1) 0): Simplify (X << C) != 0 to X
when X is zero_one_valued_p and the shift constant C is valid.
(eq (lshift @0 @1) 0): Likewise, simplify (X << C) == 0 to !X
when X is zero_one_valued_p and the shift constant C is valid.
gcc/testsuite/ChangeLog
PR tree-optimization/64992
* gcc.dg/pr64992.c: New test case.
| -rw-r--r-- | gcc/match.pd | 20 | ||||
| -rw-r--r-- | gcc/testsuite/gcc.dg/pr64992.c | 7 |
2 files changed, 27 insertions, 0 deletions
diff --git a/gcc/match.pd b/gcc/match.pd index e7d10f4..e32bda6 100644 --- a/gcc/match.pd +++ b/gcc/match.pd @@ -1920,6 +1920,26 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT) && TYPE_PRECISION (type) <= TYPE_PRECISION (TREE_TYPE (@0))) (mult (convert @1) (convert @2)))) +/* (X << C) != 0 can be simplified to X, when C is zero_one_valued_p. + Check that the shift is well-defined (C is less than TYPE_PRECISION) + as some targets (such as x86's SSE) may return zero for larger C. */ +(simplify + (ne (lshift zero_one_valued_p@0 INTEGER_CST@1) integer_zerop@2) + (if (tree_fits_shwi_p (@1) + && tree_to_shwi (@1) > 0 + && tree_to_shwi (@1) < TYPE_PRECISION (TREE_TYPE (@0))) + (convert @0))) + +/* (X << C) == 0 can be simplified to X == 0, when C is zero_one_valued_p. + Check that the shift is well-defined (C is less than TYPE_PRECISION) + as some targets (such as x86's SSE) may return zero for larger C. */ +(simplify + (eq (lshift zero_one_valued_p@0 INTEGER_CST@1) integer_zerop@2) + (if (tree_fits_shwi_p (@1) + && tree_to_shwi (@1) > 0 + && tree_to_shwi (@1) < TYPE_PRECISION (TREE_TYPE (@0))) + (eq @0 @2))) + /* Convert ~ (-A) to A - 1. */ (simplify (bit_not (convert? (negate @0))) diff --git a/gcc/testsuite/gcc.dg/pr64992.c b/gcc/testsuite/gcc.dg/pr64992.c new file mode 100644 index 0000000..43fbcf7 --- /dev/null +++ b/gcc/testsuite/gcc.dg/pr64992.c @@ -0,0 +1,7 @@ +/* { dg-do compile } */ +/* { dg-options "-O2 -fdump-tree-optimized" } */ + +_Bool foo(_Bool x) { return (x << 2) != 0; } +_Bool bar(_Bool x) { return (x << 2) == 0; } + +/* { dg-final { scan-tree-dump-not " << " "optimized" } } */ |