[X86] Don't select (cmp (and, imm), 0) to testw
Summary:
X86ISelDAGToDAG tries to analyze ANDs compared with 0 to optimize to narrower immediates using subregisters.
I don't think we should be optimizing to 16-bit test instructions. It goes against our normal behavior of promoting i16 operations to i32. It only saves one byte due to the need to add a 0x66 prefix. I think it would also be subject to a length changing prefix penalty in the decoders on Intel CPUs.
Reviewers: RKSimon, zvi, spatel
Reviewed By: spatel
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D38273
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@314474 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed