http://llvm.org/bugs/show_bug.cgi?id=21791
Bug ID: 21791
Summary: shuffling instead of moving high element directly
(x86)
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Backend: X86
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
In this test case, we want to store the high element of the vector:
$ cat get_high.ll
define void @get_high(<2 x double> %v, double* %ptr) {
%vecext1 = extractelement <2 x double> %v, i32 1
store double %vecext1, double* %ptr, align 8
ret void
}
With plain SSE2:
$ ./llc get_high.ll -o -
...
shufpd $1, %xmm0, %xmm0 ## xmm0 = xmm0[1,0]
movlpd %xmm0, (%rdi)
retq
With AVX:
$ ./llc -mcpu=btver2 get_high.ll -o -
...
vpermilpd $1, %xmm0, %xmm0 ## xmm0 = xmm0[1,0]
vmovlpd %xmm0, (%rdi)
retq
---------------------------------------------------------------------
I think we should be generating '(v)movhpd' instead; no shuffles needed.
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