http://llvm.org/bugs/show_bug.cgi?id=20714
Bug ID: 20714
Summary: SLP vectorizer cost model should handle divide by
power-of-two constants
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Backend: AArch64
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
Inspired by the equivalent X86 problem being handled in
http://reviews.llvm.org/D4971
Consider:
void f(int *restrict a, int *restrict b, int *restrict c) {
a[0] = (b[0] + c[0]) / 2;
a[1] = (b[1] + c[1]) / 2;
a[2] = (b[2] + c[2]) / 2;
a[3] = (b[3] + c[3]) / 2;
}
ARM64 can handle this via:
ldr q0, [x0]
ldr q1, [x1]
add.4s v0, v0, v1
usra.4s v0, v0, #31
sshr.4s v0, v0, #1
str q0, [x2]
Instead we generate the long scalarized sequence:
ldp w8, w9, [x1]
ldp w10, w11, [x2]
add w8, w10, w8
cmp w8, #0 ; =0
cinc w8, w8, lt
asr w8, w8, #1
str w8, [x0]
add w8, w11, w9
cmp w8, #0 ; =0
cinc w8, w8, lt
asr w8, w8, #1
str w8, [x0, #4]
ldp w8, w9, [x1, #8]
ldp w10, w11, [x2, #8]
add w8, w10, w8
cmp w8, #0 ; =0
cinc w8, w8, lt
asr w8, w8, #1
str w8, [x0, #8]
add w8, w11, w9
cmp w8, #0 ; =0
cinc w8, w8, lt
asr w8, w8, #1
str w8, [x0, #12]
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