[LLVMbugs] [Bug 15141] New: X86: Inefficient lowering of variable shl
bugzilla-daemon at llvm.org
bugzilla-daemon at llvm.org
Fri Feb 1 16:38:40 PST 2013
http://llvm.org/bugs/show_bug.cgi?id=15141
Bug #: 15141
Summary: X86: Inefficient lowering of variable shl
Product: libraries
Version: trunk
Platform: PC
OS/Version: All
Status: NEW
Severity: enhancement
Priority: P
Component: Backend: X86
AssignedTo: unassignedbugs at nondot.org
ReportedBy: nrotem at apple.com
CC: llvmbugs at cs.uiuc.edu
Classification: Unclassified
The code below is lowered to the following sequence.
23 define <4 x i32> @f22oo(<4 x i32> %in) {
24 entry:
25 %T = shl <4 x i32> %in, <i32 0, i32 1, i32 2, i32 4>
26 ret <4 x i32> %T
27 }
_f22oo: ## @f22oo
.cfi_startproc
## BB#0: ## %entry
vmovdqa LCPI2_0(%rip), %xmm1
vpslld $23, %xmm1, %xmm1
vpaddd LCPI2_1(%rip), %xmm1, %xmm1
vcvttps2dq %xmm1, %xmm1
vpmulld %xmm0, %xmm1, %xmm0
ret
.cfi_endproc
We could convert this code into "mul <1 , 2, 4, 8>".
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