[clang] [HLSL] Appropriately set function attribute optnone (PR #125937)

[S. Bharadwaj Yadavalli via cfe-commits]

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@@ -446,6 +449,13 @@ void CGHLSLRuntime::setHLSLFunctionAttributes(const FunctionDecl *FD,
     const StringRef ExportAttrKindStr = "hlsl.export";
     Fn->addFnAttr(ExportAttrKindStr);
   }
+  llvm::Triple T(Fn->getParent()->getTargetTriple());
+  if (T.getEnvironment() == llvm::Triple::EnvironmentType::Library) {
+    if (CGM.getCodeGenOpts().OptimizationLevel == 0) {
+      Fn->addFnAttr(llvm::Attribute::OptimizeNone);
+      Fn->addFnAttr(llvm::Attribute::NoInline);
+    }
+  }
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bharadwajy wrote:

> Do we want to do this on all functions in a library or just entry points and exported functions? In any case, it really would be preferable if "SetLLVMFunctionAttributesForDefinition" did the right thing (whatever that may be) rather than us needing to duplicate that logic here...

OK. It would be sufficient to set the `optnone` attribute just for entry functions of both non-library shaders and library shaders since all shaders will have one or more (respectively) entry functions. The shader flag `DisableOptimizations` can be set based on the presence of this attribute on entry function(s).

Deleted this change.

The consequences and utility in the later passes of setting `optnone` attribute for exported library functions when optimizatons are disabled is not very clear to me, yet. I'd like to propose an change, if needed, be done in a follow on PR. 

https://github.com/llvm/llvm-project/pull/125937