https://bugs.llvm.org/show_bug.cgi?id=35977
Bug ID: 35977
Summary: Vector shift misoptimized with AVX512
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Backend: X86
Assignee: unassignedb...@nondot.org
Reporter: benny....@gmail.com
CC: llvm-bugs@lists.llvm.org, llvm-...@redking.me.uk
Created attachment 19688
--> https://bugs.llvm.org/attachment.cgi?id=19688&action=edit
IR test case
The attached testcase (reduced from llvmpipe) is erroneously optimized away
when AVX512 is enabled.
$ llc -mcpu=skylake < t.ll
test: # @test
.cfi_startproc
# %bb.0: # %entry
vmovq (%rdi), %xmm0 # xmm0 = mem[0],zero
vpxor %xmm1, %xmm1, %xmm1
vpunpcklbw %xmm0, %xmm1, %xmm0 # xmm0 =
xmm1[0],xmm0[0],xmm1[1],xmm0[1],xmm1[2],xmm0[2],xmm1[3],xmm0[3],xmm1[4],xmm0[4],xmm1[5],xmm0[5],xmm1[6],xmm0[6],xmm1[7],xmm0[7]
vmovdqa %xmm0, (%rsi)
retq
$ llc -mcpu=skylake-avx512 < t.ll
test: # @test
vxorps %xmm0, %xmm0, %xmm0
vmovaps %xmm0, (%rsi)
retq
This seems to have started with r321085, but seems like an unrelated latent bug
in shuffle lowering.
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