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author | Jakub Jelinek <jakub@redhat.com> | 2024-05-08 10:17:32 +0200 |
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committer | Jakub Jelinek <jakub@redhat.com> | 2024-05-08 10:17:32 +0200 |
commit | 9adec2d91e62a479474ae79df5b455fd4b8463ba (patch) | |
tree | c85ac4d466c48f03199bfbd10af950eee5d98ba0 /gcc | |
parent | 10e34aa5b1d23e1517f0ca5cfae3cac3b51a7a53 (diff) | |
download | gcc-9adec2d91e62a479474ae79df5b455fd4b8463ba.zip gcc-9adec2d91e62a479474ae79df5b455fd4b8463ba.tar.gz gcc-9adec2d91e62a479474ae79df5b455fd4b8463ba.tar.bz2 |
reassoc: Fix up optimize_range_tests_to_bit_test [PR114965]
The optimize_range_tests_to_bit_test optimization normally emits a range
test first:
if (entry_test_needed)
{
tem = build_range_check (loc, optype, unshare_expr (exp),
false, lowi, high);
if (tem == NULL_TREE || is_gimple_val (tem))
continue;
}
so during the bit test we already know that exp is in the [lowi, high]
range, but skips it if we have range info which tells us this isn't
necessary.
Also, normally it emits shifts by exp - lowi counter, but has an
optimization to use just exp counter if the mask isn't a more expensive
constant in that case and lowi is > 0 and high is smaller than prec.
The following testcase is miscompiled because the two abnormal cases
are triggered. The range of exp is [43, 43][48, 48][95, 95], so we on
64-bit arch decide we don't need the entry test, because 95 - 43 < 64.
And we also decide to use just exp as counter, because the range test
tests just for exp == 43 || exp == 48, so high is smaller than 64 too.
Because 95 is in the exp range, we can't do that, we'd either need to
do a range test first, i.e.
if (exp - 43U <= 48U - 43U) if ((1UL << exp) & mask1))
or need to subtract lowi from the shift counter, i.e.
if ((1UL << (exp - 43)) & mask2)
but can't do both unless r.upper_bound () is < prec.
The following patch ensures that.
2024-05-08 Jakub Jelinek <jakub@redhat.com>
PR tree-optimization/114965
* tree-ssa-reassoc.cc (optimize_range_tests_to_bit_test): Don't try to
optimize away exp - lowi subtraction from shift count unless entry
test is emitted or unless r.upper_bound () is smaller than prec.
* gcc.c-torture/execute/pr114965.c: New test.
Diffstat (limited to 'gcc')
-rw-r--r-- | gcc/testsuite/gcc.c-torture/execute/pr114965.c | 30 | ||||
-rw-r--r-- | gcc/tree-ssa-reassoc.cc | 3 |
2 files changed, 32 insertions, 1 deletions
diff --git a/gcc/testsuite/gcc.c-torture/execute/pr114965.c b/gcc/testsuite/gcc.c-torture/execute/pr114965.c new file mode 100644 index 0000000..89d68e1 --- /dev/null +++ b/gcc/testsuite/gcc.c-torture/execute/pr114965.c @@ -0,0 +1,30 @@ +/* PR tree-optimization/114965 */ + +static void +foo (const char *x) +{ + + char a = '0'; + while (1) + { + switch (*x) + { + case '_': + case '+': + a = *x; + x++; + continue; + default: + break; + } + break; + } + if (a == '0' || a == '+') + __builtin_abort (); +} + +int +main () +{ + foo ("_"); +} diff --git a/gcc/tree-ssa-reassoc.cc b/gcc/tree-ssa-reassoc.cc index 61f54f0..556ecde 100644 --- a/gcc/tree-ssa-reassoc.cc +++ b/gcc/tree-ssa-reassoc.cc @@ -3418,7 +3418,8 @@ optimize_range_tests_to_bit_test (enum tree_code opcode, int first, int length, We can avoid then subtraction of the minimum value, but the mask constant could be perhaps more expensive. */ if (compare_tree_int (lowi, 0) > 0 - && compare_tree_int (high, prec) < 0) + && compare_tree_int (high, prec) < 0 + && (entry_test_needed || wi::ltu_p (r.upper_bound (), prec))) { int cost_diff; HOST_WIDE_INT m = tree_to_uhwi (lowi); |