[llvm] [DirectX] Propagate shader flags mask of callees to callers (PR #118306)

[S. Bharadwaj Yadavalli via llvm-commits]

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@@ -81,16 +101,31 @@ void ComputedShaderFlags::print(raw_ostream &OS) const {
   OS << ";\n";
 }
 
-/// Return the shader flags mask of the specified function Func.
-const ComputedShaderFlags &
-ModuleShaderFlags::getFunctionFlags(const Function *Func) const {
+auto ModuleShaderFlags::getFunctionShaderFlagInfo(const Function *Func) const {
   const auto Iter = llvm::lower_bound(
       FunctionFlags, Func,
       [](const std::pair<const Function *, ComputedShaderFlags> FSM,
          const Function *FindFunc) { return (FSM.first < FindFunc); });
   assert((Iter != FunctionFlags.end() && Iter->first == Func) &&
          "No Shader Flags Mask exists for function");
-  return Iter->second;
+  return Iter;
+}
+
+/// Merge mask NewSF to that of Func, if different.
+/// Return true if mask of Func is changed, else false.
+bool ModuleShaderFlags::mergeFunctionShaderFlags(
+    const Function *Func, const ComputedShaderFlags NewSF) {
+  const auto FuncSFInfo = getFunctionShaderFlagInfo(Func);
+  if ((FuncSFInfo->second & NewSF) != NewSF) {
+    const_cast<ComputedShaderFlags &>(FuncSFInfo->second).merge(NewSF);
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bharadwajy wrote:

Changed `merge()` to operate on `ComputeShaderFlags` type thereby not relying on implicit cast to `uint64_t`.

Updated `mergeFunctionShaderFlags()` with the check for shader flag value change.

However, testing for equality still implicitly casts to `uint64_t`. Getting rid of implicit conversion operator requires changes to other access functions such as `getFeatureFlags()` etc., that use the conversion. I'll plan to delete implicit conversion operator in a follow-on PR. I think this implies that `operator==` would need to be implemented. Created an [issue](https://github.com/llvm/llvm-project/issues/118570) for this.

https://github.com/llvm/llvm-project/pull/118306