[clang] [Clang] Add fake use emission to Clang with -fextend-lifetimes (PR #110102)

[Jeremy Morse via cfe-commits]

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@@ -1664,6 +1710,17 @@ CodeGenFunction::EmitAutoVarAlloca(const VarDecl &D) {
                                          emission.getOriginalAllocatedAddress(),
                                          emission.getSizeForLifetimeMarkers());
 
+  // Analogous to lifetime markers, we use a 'cleanup' to emit fake.use
+  // calls for local variables. We are exempting volatile variables and
+  // non-scalars larger than 4 times the size of an unsigned int (32 bytes).
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jmorse wrote:

16 bytes presumably, or 32 bits for unsigned int? Best to avoid being too specific IMO as it's machine dependent. (Perhaps all the world's a VAX, but we can avoid saying it in comments).

https://github.com/llvm/llvm-project/pull/110102