https://llvm.org/bugs/show_bug.cgi?id=30264
Bug ID: 30264
Summary: [InstCombine] reduce shuffles with constants to a
single shuffle
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Scalar Optimizations
Assignee: unassignedb...@nondot.org
Reporter: spatel+l...@rotateright.com
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
I noticed this case in https://reviews.llvm.org/D24182 :
define <4 x float> @insertConstants(<4 x float> %x) {
%shuf1 = shufflevector <4 x float> %x, <4 x float> <float undef, float 0.0,
float undef, float undef>, <4 x i32> <i32 0, i32 5, i32 undef, i32 undef>
%shuf2 = shufflevector <4 x float> %shuf1, <4 x float> <float undef, float
undef, float 4.0, float 1.0>, <4 x i32> <i32 0, i32 1, i32 6, i32 7>
ret <4 x float> %shuf2
}
This can be combined into one shuffle instruction that we can assume is as
cheap as either of the original ones:
shufflevector <4 x float> %x, <4 x float> <float undef, float 0.0, float 4.0,
float 1.0>, <4 x i32> <i32 0, i32 5, i32 6, i32 7>
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