[clang] [llvm] [X86] Support apxf in attribute target (PR #184078)

[Mikołaj Piróg via cfe-commits]

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@@ -179,10 +179,15 @@ bool X86TargetInfo::initFeatureMap(
       continue;
     }
 
+    if (llvm::X86::expandAPXFeatures(Feature, getTriple(), UpdatedFeaturesVec))
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mikolaj-pirog wrote:

| We always add more features to single functions rather than reduce

An organic example I can think of where one would like to remove features is this: when the compiler does a bad job and some specific function with a feature regresses, but at the same time other functions don't. You can then use negative feature in attribute target to remove this feature from a single function.

It also doesn't really cost us anything to support negative feature, given the machinery is already there

https://github.com/llvm/llvm-project/pull/184078