http://llvm.org/bugs/show_bug.cgi?id=21137
Bug ID: 21137
Summary: Missing memory folding with new vector shuffle
lowering.
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Backend: X86
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
Created attachment 13121
--> http://llvm.org/bugs/attachment.cgi?id=13121&action=edit
IR to reproduce the problem
When using the new vector shuffle lowering, some folding opportunities are
missed.
To reproduce:
llc -x86-experimental-vector-shuffle-lowering=true missing_folding.ll -o new.s
llc -x86-experimental-vector-shuffle-lowering=false missing_folding.ll -o old.s
diff -U 10 old.s new.s
- pshufd $27, (%rdi), %xmm0 ## xmm0 = mem[3,2,1,0]
+ movaps (%rdi), %xmm0
+ shufps $27, %xmm0, %xmm0 ## xmm0 = xmm0[3,2,1,0]
The shuffle instruction used in the new lowering is on a different than the old
one (different domain). Thus, it is likely we need to teach how to fold the
operand for that one too.
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