[clang] [HLSL] set alwaysinline on HLSL functions (PR #106588)

[Greg Roth via cfe-commits]

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@@ -2474,7 +2474,9 @@ void CodeGenModule::SetLLVMFunctionAttributesForDefinition(const Decl *D,
     // If we don't have a declaration to control inlining, the function isn't
     // explicitly marked as alwaysinline for semantic reasons, and inlining is
     // disabled, mark the function as noinline.
+    // HLSL functions must be always inlined
     if (!F->hasFnAttribute(llvm::Attribute::AlwaysInline) &&
+        !getLangOpts().HLSL &&
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pow2clk wrote:

I investigated this in some depth. The situation is that the autogenerated initialization and destruction functions get their attributes set through this call and others before their bodies are generated, which calls `setHLSLFunctionAttributes` while user functions generate their bodies and make the hlsl attributes call before this one. This seems error-prone to me, but the code has been around long enough that I'm not ready to go changing it even though some initial experiments showed no regressions. 

In the meantime, since so much inline attribute logic is in this function, I've concluded that the best solution is to add our inline logic here and not in `setHLSLFunctionAttributes` at all. That way it doesn't matter as much where in the IR function creation process it takes place and any consequences can be accounted for along with the existing logic. That's what my latest commit does. 

https://github.com/llvm/llvm-project/pull/106588