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[Intrinsic] Expand SMULFIX to MUL, MULH[US], or [US]MUL_LOHI on vector arguments

Authored by leonardchan on Jan 31 2019, 11:15 AM.

Description

[Intrinsic] Expand SMULFIX to MUL, MULH[US], or [US]MUL_LOHI on vector arguments

r zero scale SMULFIX, expand into MUL which produces better code for X86.

For vector arguments, expand into MUL if SMULFIX is provided with a zero scale.
Otherwise, expand into MULH[US] or [US]MUL_LOHI.

Differential Revision: https://reviews.llvm.org/D56987

llvm-svn: 352783