[Bug target/80517] [missed optimization] constant propagation through Intel intrinsics
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80517 Andrew Pinski changed: What|Removed |Added See Also||https://gcc.gnu.org/bugzill ||a/show_bug.cgi?id=24928 --- Comment #8 from Andrew Pinski --- status of this bug: comment #0 first testcase: Fixed since GCC 9 comment #0 second testcase: still needs improvement comment #3 is now basically PR 24928
[Bug target/80517] [missed optimization] constant propagation through Intel intrinsics
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80517 Andrew Pinski changed: What|Removed |Added Severity|normal |enhancement
[Bug target/80517] [missed optimization] constant propagation through Intel intrinsics
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80517 --- Comment #7 from Uroš Bizjak --- See also PR55894.
[Bug target/80517] [missed optimization] constant propagation through Intel intrinsics
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80517 --- Comment #6 from Marc Glisse --- (In reply to Matthias Kretz from comment #4) > A similar test case showing that something is still missing You don't seem to be passing constants here, so this is unrelated to this PR. If you file a new one, please annotate your example explaining where you expect what to simplify to what and why. > (https://gcc.godbolt.org/z/t1DT7E): Adding -fdump-tree-optimized=- -g0 and showing the compiler output makes this more understandable for me...
[Bug target/80517] [missed optimization] constant propagation through Intel intrinsics
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80517
--- Comment #5 from Marc Glisse ---
(In reply to Matthias Kretz from comment #3)
> GCC 9 almost resolves this. However, for some reason this extended test case
> is not fully optimized: https://gcc.godbolt.org/z/jRrHth
> i.e. the call to dont_call_me() should be eliminated as dead code
We are left with:
_GLOBAL__sub_I__Z1fv ()
{
[local count: 1073741824]:
d = 125;
return;
}
f ()
{
unsigned int d.1_1;
[local count: 1073741824]:
d.1_1 = d;
if (d.1_1 == 125)
[...]
This is a classic, if the initialization of global variables is only noticed to
be constant after optimizations (as opposed to in the front-end), gcc doesn't
manage to turn the dynamic initialization into a static one. Making the
intrinsics constexpr may help, but really this is something that would be nice
to fix eventually, there are several PRs blocked by this.
[Bug target/80517] [missed optimization] constant propagation through Intel intrinsics
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80517
--- Comment #4 from Matthias Kretz ---
A similar test case showing that something is still missing
(https://gcc.godbolt.org/z/t1DT7E):
#include
inline __m128i cmp(__m128i x, __m128i y) {
return _mm_cmpeq_epi16(x, y);
}
inline unsigned to_bits(__m128i mask0) {
return _pext_u32(_mm_movemask_epi8(mask0), 0x);
}
inline __m128i to_vmask(unsigned bits) {
__m128i mask = _mm_set1_epi16(bits);
mask = _mm_and_si128(mask, _mm_setr_epi16(1, 2, 4, 8, 16, 32, 64, 128));
mask = _mm_cmpeq_epi16(mask, _mm_setzero_si128());
mask = _mm_xor_si128(mask, _mm_cmpeq_epi16(mask, mask));
return mask;
}
auto f(__m128i x, __m128i y) {
// should be:
// vpcmpeqw %xmm1, %xmm0, %xmm0
// ret
return to_vmask(to_bits(cmp(x, y)));
}
auto f(unsigned bits) {
// should be equivalent to `return 0xff & bits;`
return to_bits(to_vmask(bits));
}
[Bug target/80517] [missed optimization] constant propagation through Intel intrinsics
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80517
Matthias Kretz changed:
What|Removed |Added
Version|8.0 |9.0
--- Comment #3 from Matthias Kretz ---
GCC 9 almost resolves this. However, for some reason this extended test case is
not fully optimized: https://gcc.godbolt.org/z/jRrHth
i.e. the call to dont_call_me() should be eliminated as dead code
#include
inline __m128i cmp(__m128i x, __m128i y) {
return _mm_cmpeq_epi16(x, y);
}
inline unsigned to_bits(__m128i mask0) {
return _pext_u32(_mm_movemask_epi8(mask0), 0x);
}
inline __m128i to_vmask(unsigned bits) {
__m128i mask = _mm_set1_epi16(bits);
mask = _mm_and_si128(mask, _mm_setr_epi16(1, 2, 4, 8, 16, 32, 64, 128));
mask = _mm_cmpeq_epi16(mask, _mm_setzero_si128());
mask = _mm_xor_si128(mask, _mm_cmpeq_epi16(mask, mask));
return mask;
}
inline bool is_eq(unsigned bits, __m128i vmask) {
return to_bits(vmask) == bits;
}
extern const auto a = __m128i{0x0001'0002'0004'0003, 0x0009'0008'0007'0006};
extern const auto b = __m128i{0x0001'0002'0005'0003, 0x'0008'0007'0006};
extern const auto c = cmp(a, b);
extern const auto d = to_bits(c);
void call_me();
void dont_call_me();
void f() {
if (is_eq(d, cmp(b, a))) {
call_me();
} else {
dont_call_me();
}
}
[Bug target/80517] [missed optimization] constant propagation through Intel intrinsics
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80517 Richard Biener changed: What|Removed |Added Keywords||missed-optimization Target||x86_64-*-*, i?86-*-* Status|UNCONFIRMED |NEW Last reconfirmed||2017-04-26 Ever confirmed|0 |1 --- Comment #2 from Richard Biener --- Confirmed.
[Bug target/80517] [missed optimization] constant propagation through Intel intrinsics
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80517 --- Comment #1 from Marc Glisse --- Several of those intrinsics are implemented using vector extensions and constant propagation works fine on those. What seems to be missing here is constant folding of the very specific __builtin_ia32_pmovmskb128 and __builtin_ia32_pext_si in ix86_fold_builtin. It should not be very hard, mostly needs someone motivated ;-)
