[PATCH] D143471: [X86][MC][NFC] Refine code in X86MCCodeEmitter.cpp about opcode prefix

[Kan Shengchen via Phabricator via llvm-commits]

skan added a comment.

In D143471#4117637 <https://reviews.llvm.org/D143471#4117637>, @uabelho wrote:

> Hi,
>
> I noticed that if I run lit tests with ubsan built binaries with this patch there are many many tests failing like
>
>   ../lib/Target/X86/MCTargetDesc/X86MCCodeEmitter.cpp:222:19: runtime error: left shift of negative value -1

I think it's false positive?

  ~R << 7

`R` is an `unsigned`, so `~R` is `unsigned` too. Although the value of `~R` may be `0xffffffff`. But I remember the left shift operation on `unsigned` is always well defined.


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https://reviews.llvm.org/D143471