[clang] [clang] Function type attribute to prevent CFI instrumentation (PR #135836)

[Aaron Ballman via cfe-commits]

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@@ -1988,7 +1988,7 @@ class alignas(TypeAlignment) Type : public ExtQualsTypeCommonBase {
     /// Extra information which affects how the function is called, like
     /// regparm and the calling convention.
     LLVM_PREFERRED_TYPE(CallingConv)
-    unsigned ExtInfo : 14;
+    unsigned ExtInfo : 15;
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AaronBallman wrote:

This is correct, but it is using the last bit we have available. Any other bits we need will mean we're making this object significantly larger which is going to have some serious performance overhead concerns given how many functions appear in a TU, or we're reducing the number of parameters we support in a function declaration (cutting that value in half, at least).

Are we sure we want to use this bit for these purposes?

https://github.com/llvm/llvm-project/pull/135836