https://llvm.org/bugs/show_bug.cgi?id=31879
Bug ID: 31879
Summary: vectorize repeated scalar ops that don't get put back
into a vector
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Transformation Utilities
Assignee: unassignedb...@nondot.org
Reporter: spatel+l...@rotateright.com
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
Forking this off from bug 31866:
; For vector <x0, x1>, return x0^2 + x1^2
define float @f(<2 x float> %x) {
%x0 = extractelement <2 x float> %x, i32 0
%x1 = extractelement <2 x float> %x, i32 1
%x0x0 = fmul float %x0, %x0
%x1x1 = fmul float %x1, %x1
%add = fadd float %x0x0, %x1x1
ret float %add
}
We should recognize patterns where the same scalar ops are applied to all
extracted elements in a vector and turn that into vector ops followed by
extraction:
define float @f(<2 x float> %x) {
%xx = fmul <2 x float> %x, %x
%x0x0 = extractelement <2 x float> %xx, i32 0
%x1x1 = extractelement <2 x float> %xx, i32 1
%add = fadd float %x0x0, %x1x1
ret float %add
}
The SLP vectorizer already handles the case where we insert back into a vector,
so we can loosen the restriction and use the existing SLP logic to catch this
case?
define <2 x i8> @g(<2 x i8> %x) {
%x0 = extractelement <2 x i8> %x, i32 0
%x1 = extractelement <2 x i8> %x, i32 1
%x0x0 = mul i8 %x0, %x0
%x1x1 = mul i8 %x1, %x1
%ins1 = insertelement <2 x i8> undef, i8 %x0x0, i32 0
%ins2 = insertelement <2 x i8> %ins1, i8 %x1x1, i32 1
ret <2 x i8> %ins2
}
$ ./opt -slp-vectorizer scalarizedmath.ll -S
define <2 x i8> @g(<2 x i8> %x) {
%1 = mul <2 x i8> %x, %x
%2 = extractelement <2 x i8> %1, i32 0
%ret = insertelement <2 x i8> undef, i8 %2, i32 0
%3 = extractelement <2 x i8> %1, i32 1
%ret2 = insertelement <2 x i8> %ret, i8 %3, i32 1
ret <2 x i8> %ret2
}
Instcombine can then clean up the useless inserts and extracts.
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