https://bugs.llvm.org/show_bug.cgi?id=37502
Bug ID: 37502
Summary: _mm_set_ps is lowered badly with sse4
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: enhancement
Priority: P
Component: Backend: X86
Assignee: unassignedb...@nondot.org
Reporter: jmuizel...@mozilla.com
CC: llvm-bugs@lists.llvm.org
__m128 f(float aYScale, float aXScale) {
return _mm_set_ps(aYScale, aXScale, aYScale, aXScale);
}
With -mssse3 this compiles to:
unpcklps %xmm0, %xmm1 # xmm1 =
xmm1[0],xmm0[0],xmm1[1],xmm0[1]
movddup %xmm1, %xmm0 # xmm0 = xmm1[0,0]
with -mssse4 this compiles to:
movaps %xmm1, %xmm2
insertps $16, %xmm0, %xmm2 # xmm2 = xmm2[0],xmm0[0],xmm2[2,3]
insertps $32, %xmm1, %xmm2 # xmm2 = xmm2[0,1],xmm1[0],xmm2[3]
insertps $48, %xmm0, %xmm2 # xmm2 = xmm2[0,1,2],xmm0[0]
movaps %xmm2, %xmm0
llvm-mca -mcpu=haswell agrees that the ssse3 version is better:
Iterations: 1
Instructions: 2
Total Cycles: 5
Dispatch Width: 4
IPC: 0.40
vs
Iterations: 1
Instructions: 5
Total Cycles: 8
Dispatch Width: 4
IPC: 0.62
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