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| author | Eugene Rozenfeld <erozen@microsoft.com> | 2020-11-05 20:35:45 -0700 |
|---|---|---|
| committer | Jeff Law <law@redhat.com> | 2020-11-05 20:35:45 -0700 |
| commit | 6483f05989ef31ebf2583deeb4753211ca2b7e17 (patch) | |
| tree | 8c0622b9a031143be1cf642c310c5af5788b9080 /gcc | |
| parent | 56ecdc2f02bfa69021003d7ac267dc65f385902f (diff) | |
| download | gcc-6483f05989ef31ebf2583deeb4753211ca2b7e17.zip gcc-6483f05989ef31ebf2583deeb4753211ca2b7e17.tar.gz gcc-6483f05989ef31ebf2583deeb4753211ca2b7e17.tar.bz2 | |
Simplify x >> x to 0. This fixes PR96701.
gcc/
* match.pd (x >> x): New pattern.
gcc/testsuite
* gcc.dg/self-right-shift.c: New test.
Diffstat (limited to 'gcc')
| -rw-r--r-- | gcc/match.pd | 5 | ||||
| -rw-r--r-- | gcc/testsuite/gcc.dg/self-right-shift.c | 12 |
2 files changed, 17 insertions, 0 deletions
diff --git a/gcc/match.pd b/gcc/match.pd index 17ba041..d82a620 100644 --- a/gcc/match.pd +++ b/gcc/match.pd @@ -2925,6 +2925,11 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT) && (wi::ltu_p (wi::to_wide (@1), element_precision (type)))) (bit_and @0 (rshift { build_minus_one_cst (type); } @1)))) +/* Optimize x >> x into 0 */ +(simplify + (rshift @0 @0) + { build_zero_cst (type); }) + (for shiftrotate (lrotate rrotate lshift rshift) (simplify (shiftrotate @0 integer_zerop) diff --git a/gcc/testsuite/gcc.dg/self-right-shift.c b/gcc/testsuite/gcc.dg/self-right-shift.c new file mode 100644 index 0000000..c457ee5 --- /dev/null +++ b/gcc/testsuite/gcc.dg/self-right-shift.c @@ -0,0 +1,12 @@ +/* { dg-do compile } */ +/* { dg-options "-O2 -fdump-tree-optimized" } */ + +/* Self right-shift should be optimized to 0. */ + +int +foo (int i) +{ + return i >> i; +} + +/* { dg-final { scan-tree-dump "return 0;" "optimized" } } */ |