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| author | Jakub Jelinek <jakub@redhat.com> | 2010-09-13 23:00:03 +0200 |
|---|---|---|
| committer | Jakub Jelinek <jakub@gcc.gnu.org> | 2010-09-13 23:00:03 +0200 |
| commit | ef3be7da315db90f5d311b43464c5341fa33d5e2 (patch) | |
| tree | 142dc459a1da90111739127e8c28d54c9c9564e9 /gcc/combine.c | |
| parent | fa0921fcd0c899546fe2d4f6f4cee0ab01ea97eb (diff) | |
| download | gcc-ef3be7da315db90f5d311b43464c5341fa33d5e2.zip gcc-ef3be7da315db90f5d311b43464c5341fa33d5e2.tar.gz gcc-ef3be7da315db90f5d311b43464c5341fa33d5e2.tar.bz2 | |
re PR rtl-optimization/45617 (optimize bit shift+compare at RTL level)
PR rtl-optimization/45617
* combine.c (simplify_comparison): Optimize (X >> N) {>,>=,<,<=} C
even if low N bits of X aren't known to be zero.
* gcc.target/i386/pr45617.c: New test.
From-SVN: r164257
Diffstat (limited to 'gcc/combine.c')
| -rw-r--r-- | gcc/combine.c | 39 |
1 files changed, 26 insertions, 13 deletions
diff --git a/gcc/combine.c b/gcc/combine.c index bed5768..618e07d 100644 --- a/gcc/combine.c +++ b/gcc/combine.c @@ -11773,13 +11773,14 @@ simplify_comparison (enum rtx_code code, rtx *pop0, rtx *pop1) /* If we have (compare (xshiftrt FOO N) (const_int C)) and the low order N bits of FOO are known to be zero, we can do this by comparing FOO with C shifted left N bits so long as no - overflow occurs. */ + overflow occurs. Even if the low order N bits of FOO aren't known + to be zero, if the comparison is >= or < we can use the same + optimization and for > or <= by setting all the low + order N bits in the comparison constant. */ if (CONST_INT_P (XEXP (op0, 1)) - && INTVAL (XEXP (op0, 1)) >= 0 + && INTVAL (XEXP (op0, 1)) > 0 && INTVAL (XEXP (op0, 1)) < HOST_BITS_PER_WIDE_INT && mode_width <= HOST_BITS_PER_WIDE_INT - && (nonzero_bits (XEXP (op0, 0), mode) - & (((HOST_WIDE_INT) 1 << INTVAL (XEXP (op0, 1))) - 1)) == 0 && (((unsigned HOST_WIDE_INT) const_op + (GET_CODE (op0) != LSHIFTRT ? ((GET_MODE_MASK (mode) >> INTVAL (XEXP (op0, 1)) >> 1) @@ -11787,15 +11788,27 @@ simplify_comparison (enum rtx_code code, rtx *pop0, rtx *pop1) : 0)) <= GET_MODE_MASK (mode) >> INTVAL (XEXP (op0, 1)))) { - /* If the shift was logical, then we must make the condition - unsigned. */ - if (GET_CODE (op0) == LSHIFTRT) - code = unsigned_condition (code); - - const_op <<= INTVAL (XEXP (op0, 1)); - op1 = GEN_INT (const_op); - op0 = XEXP (op0, 0); - continue; + unsigned HOST_WIDE_INT low_bits + = (nonzero_bits (XEXP (op0, 0), mode) + & (((unsigned HOST_WIDE_INT) 1 + << INTVAL (XEXP (op0, 1))) - 1)); + if (low_bits == 0 || !equality_comparison_p) + { + /* If the shift was logical, then we must make the condition + unsigned. */ + if (GET_CODE (op0) == LSHIFTRT) + code = unsigned_condition (code); + + const_op <<= INTVAL (XEXP (op0, 1)); + if (low_bits != 0 + && (code == GT || code == GTU + || code == LE || code == LEU)) + const_op + |= (((HOST_WIDE_INT) 1 << INTVAL (XEXP (op0, 1))) - 1); + op1 = GEN_INT (const_op); + op0 = XEXP (op0, 0); + continue; + } } /* If we are using this shift to extract just the sign bit, we |