https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82281
Bug ID: 82281
Summary: Bulldozer/Zen tuning: uses XMM for single 64-bit
integer AND, even with a simple mask
Product: gcc
Version: 8.0
Status: UNCONFIRMED
Keywords: missed-optimization, ssemmx
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: peter at cordes dot ca
Target Milestone: ---
long long test_and(long long x) {
return x & 0x77ffffffffULL;
}
// https://godbolt.org/g/D6XujV
# -O3 -march=znver1 -m32 -mno-avx
movaps .LC0, %xmm1
movq 4(%esp), %xmm0
andps %xmm1, %xmm0
movd %xmm0, %eax
pextrd $1, %xmm0, %edx
ret
# -O3 -m32
movl 8(%esp), %edx
movl 4(%esp), %eax
andl $119, %edx
ret
We get this with znver1 and bdver1-4, but not barcelona or btver2.
Also not haswell, skylake or knl.
So something is wrong with tunings for recent AMD that make it over-eager to go
to vector registers for 64-bit integers in the most trivial case possible.
Fortunately it's on when coming from memory:
long long ext();
long long test_and() {
long long x = ext();
return x & 0x77ffffffffULL;
}
# -O3 -march=znver1 -m32
subl $12, %esp
call ext()
addl $12, %esp
andl $119, %edx
ret
