https://bugs.llvm.org/show_bug.cgi?id=44588
Bug ID: 44588
Summary: [InstCombine] icmp not pushed through shufflevector
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: Scalar Optimizations
Assignee: unassignedbugs at nondot.org
Reporter: nikita.ppv at gmail.com
CC: llvm-bugs at lists.llvm.org, llvm-dev at redking.me.uk,
spatel+llvm at rotateright.com
Instcombine pushes binary operations through shufflevector instructions,
however the same does not happen with icmps:
define <2 x i1> @test(i64 %X) {
%.splatinsert = insertelement <2 x i64> undef, i64 %X, i32 0
%.splat = shufflevector <2 x i64> %.splatinsert, <2 x i64> undef, <2 x i32>
zeroinitializer
%A.idx = mul nsw <2 x i64> %.splat, <i64 4, i64 4>
%A.offs = add <2 x i64> %A.idx, <i64 4, i64 4>
%C = icmp eq <2 x i64> %A.offs, <i64 4, i64 4>
ret <2 x i1> %C
}
opt -instcombine
define <2 x i1> @test(i64 %X) {
%.splatinsert = insertelement <2 x i64> undef, i64 %X, i32 0
%1 = shl <2 x i64> %.splatinsert, <i64 2, i64 undef>
%2 = add <2 x i64> %1, <i64 4, i64 undef>
%A.offs = shufflevector <2 x i64> %2, <2 x i64> undef, <2 x i32>
zeroinitializer
%C = icmp eq <2 x i64> %A.offs, <i64 4, i64 4>
ret <2 x i1> %C
}
This means that the add+eq pair that would normally get folded ends up
separated by a shufflevector.
(As a side-note, it seems like there's an opportunity here to push instructions
through insertelement if the other lanes are undef anyway.)
--
You are receiving this mail because:
You are on the CC list for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-bugs/attachments/20200119/8c69c18e/attachment-0001.html>