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

[S. Bharadwaj Yadavalli via llvm-commits]

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@@ -46,21 +49,79 @@ static void updateFunctionFlags(ComputedShaderFlags &CSF,
   }
 }
 
-void ModuleShaderFlags::initialize(const Module &M) {
-  // Collect shader flags for each of the functions
-  for (const auto &F : M.getFunctionList()) {
-    if (F.isDeclaration())
+void ModuleShaderFlags::initialize(Module &M) {
+  CallGraph CG(M);
+
+  // Compute Shader Flags Mask for all functions using post-order visit of SCC
+  // of the call graph.
+  for (scc_iterator<CallGraph *> SCCI = scc_begin(&CG); !SCCI.isAtEnd();
+       ++SCCI) {
+    const std::vector<CallGraphNode *> &CurSCC = *SCCI;
+
+    // Union of shader masks of all functions in CurSCC
+    ComputedShaderFlags SCCSF;
+    for (CallGraphNode *CGN : CurSCC) {
+      Function *F = CGN->getFunction();
+      if (!F)
+        continue;
+
+      if (F->isDeclaration())
+        continue;
+
+      ComputedShaderFlags CSF;
+      for (const auto &BB : *F)
+        for (const auto &I : BB)
+          updateFunctionFlags(CSF, I);
+      // Insert shader flag mask for function F
+      FunctionFlags.insert({F, CSF});
+      // Update combined shader flags mask for all functions of the module
+      CombinedSFMask.merge(CSF);
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bharadwajy wrote:

> Since we have to calculate SCCSF anyways, we can hoist the merge of the combined mask out of this loop

Changed.

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