http://llvm.org/bugs/show_bug.cgi?id=22413
Bug ID: 22413
Summary: New vector shuffle legality: turns movss (SSE2) or
blendps (SSE4.2+) into shufps.
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
Created attachment 13785
--> http://llvm.org/bugs/attachment.cgi?id=13785&action=edit
IR testcase
For the attached IR, we used to generate (for SSE2, but the AVX2 and SSE4.2
outputs are similarly interesting):
movss %xmm1, %xmm0
shufps $51, %xmm0, %xmm0 ## xmm0 = xmm0[3,0,3,0]
movaps %xmm0, (%rdi)
With the new all-shuffles-are-legal lowering, we now generate:
shufps $15, %xmm1, %xmm0 ## xmm0 = xmm0[3,3],xmm1[0,0]
shufps $216, %xmm0, %xmm0 ## xmm0 = xmm0[0,2,1,3]
movaps %xmm0, (%rdi)
The example is a bit harmless, so there's another, more interesting, one, in
the attached IR.
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