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Add comment to explain a non-obvious setting; NFC.

This is paraphrased from Simon Pilgrim's comment in:
http://reviews.llvm.org/D7492

llvm-svn: 229566
This commit is contained in:
Sanjay Patel 2015-02-17 22:09:54 +00:00
parent f2c498a0c4
commit 60b8b1a43f

View File

@ -657,6 +657,12 @@ X86InstrInfo::X86InstrInfo(X86Subtarget &STI)
{ X86::VTESTPSYrr, X86::VTESTPSYrm, 0 },
// AVX2 foldable instructions
// VBROADCASTS{SD}rr register instructions were an AVX2 addition while the
// VBROADCASTS{SD}rm memory instructions were available from AVX1.
// TB_NO_REVERSE prevents unfolding from introducing an illegal instruction
// on AVX1 targets. The VPBROADCAST instructions are all AVX2 instructions
// so they don't need an equivalent limitation.
{ X86::VBROADCASTSSrr, X86::VBROADCASTSSrm, TB_NO_REVERSE },
{ X86::VBROADCASTSSYrr, X86::VBROADCASTSSYrm, TB_NO_REVERSE },
{ X86::VBROADCASTSDYrr, X86::VBROADCASTSDYrm, TB_NO_REVERSE },