[llvm-bugs] [Bug 32255] New: [X86] Should we use ExeDepsFix to optimize unused input to gather instructions?
llvm-bugs at lists.llvm.org
Mon Mar 13 11:51:17 PDT 2017
Bug ID: 32255
Summary: [X86] Should we use ExeDepsFix to optimize unused
input to gather instructions?
Component: Backend: X86
Assignee: unassignedbugs at nondot.org
Reporter: craig.topper at gmail.com
CC: llvm-bugs at lists.llvm.org
If the gather mask is all ones or the input is undef, we force the input to a
zero vector during lowering. It may be better to instead force the input to
undef and let ExeDepsFix handle clearance checking.
We need to be careful though because I think ExeDepsFix will first try to tie
the input to the VSIB index register since that's already an input. We would
need to teach ExeDepsFix about the early clobber restriction on the source
register that makes that illegal.
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