[llvm] [DirectX] Set Shader Flag DisableOptimizations. (PR #123136)

[S. Bharadwaj Yadavalli via llvm-commits]

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@@ -68,6 +68,37 @@ static ModuleMetadataInfo collectMetadataInfo(Module &M) {
     }
     MMDAI.EntryPropertyVec.push_back(EFP);
   }
+
+  // Set shader flags based on Module properties
+  SmallVector<llvm::Module::ModuleFlagEntry> FlagEntries;
+  SmallVector<llvm::Module::ModuleFlagEntry> NewFlagEntries;
+  M.getModuleFlagsMetadata(FlagEntries);
+  for (const auto &Flag : FlagEntries) {
+    if ((Flag.Behavior == Module::ModFlagBehavior::Override) &&
+        (Flag.Key->getString().compare("dx.disable_optimizations") == 0)) {
+      const auto *V = mdconst::extract<llvm::ConstantInt>(Flag.Val);
+      if (V->isOne())
+        MMDAI.DisableOptimizations = true;
+    } else
+      // Collect all Module Flags other than dx.disable_optimizations.
+      NewFlagEntries.push_back(Flag);
+  }
+
+  // "dx.disable_optimizations" is not included in the metadata specified in
+  // DXIL specification. Hence it needs to be deleted such that it is not
+  // emitted in the final DXIL output, now that its intent is captured in MMDAI,
+  // if present.
+
+  if (NewFlagEntries.size() != FlagEntries.size()) {
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bharadwajy wrote:

> Do we need to do this here? We have code in DXILPrepare that cleans the module flags.
> 
> @bogner, I think the reason the `dx.disable_optimizations` named metadata wasn't causing issues is because DXIL doesn't use custom module flags at all, so in DXILPrepare we just strip out any non-standard LLVM 3.7 module flags, which will clean this up.

@llvm-beanz I [proposed a PR](#125937) to decorate shader entry functions with the attribute `optnone` as an alternative to using `dx.disable_optimizations` named metadata - per feedback [above](#issuecomment-2611684827). 

The idea is to eliminate creation of `dx.disable_optimizations` metadata and key off the `optnone` attribute on shader entry functions to set the shader flag `DisableOptimizations` as implemented [here](https://github.com/llvm/llvm-project/compare/main...bharadwajy:llvm-project:delete-disable-opt-metadata?expand=1) with an expectation of converting it to a follow-on PR to #125937.

I'd appreciate a feedback on #125937 in this context as well as the preferred choice compared to this PR.

https://github.com/llvm/llvm-project/pull/123136