[x86] Flip the sentinel values used in the target shuffle mask decoding

to significantly more sane sentinels. Notably, everywhere else in the
backend's representation of shuffles uses '-1' to represent undef. The
target shuffle masks really shouldn't diverge from that, especially as
in a few places they are manipulated by shared code.

This causes us to lose some undef lanes in various test masks. I want to
get these back, but technically it isn't invalid and there are a *lot*
of bugs here so I want to try to establish a saner baseline for fixing
some of the bugs by aligning the specific senitnel values used.

llvm-svn: 218561

1 files changed, 1 insertions, 1 deletions

diff --git a/llvm/lib/Target/X86/Utils/X86ShuffleDecode.h b/llvm/lib/Target/X86/Utils/X86ShuffleDecode.h
index ece895d77cc..af26d0a509b 100644
--- a/llvm/lib/Target/X86/Utils/X86ShuffleDecode.h
+++ b/llvm/lib/Target/X86/Utils/X86ShuffleDecode.h
@@ -26,7 +26,7 @@ namespace llvm {
 class Constant;
 class MVT;
 
-enum { SM_SentinelZero = -1, SM_SentinelUndef = -2 };
+enum { SM_SentinelUndef = -1, SM_SentinelZero = -2 };
 
 void DecodeINSERTPSMask(unsigned Imm, SmallVectorImpl<int> &ShuffleMask);