[clang] [llvm] [AMDGPU] Infer amdgpu-no-flat-scratch-init attribute in AMDGPUAttributor (PR #94647)

[Matt Arsenault via cfe-commits]

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@@ -678,6 +690,37 @@ struct AAAMDAttributesFunction : public AAAMDAttributes {
     return !A.checkForAllCallLikeInstructions(DoesNotRetrieve, *this,
                                               UsedAssumedInformation);
   }
+
+  // Returns true if FlatScratchInit is needed, i.e., no-flat-scratch-init is
+  // not to be set.
+  bool needFlatScratchInit(Attributor &A) {
+    assert(isAssumed(FLAT_SCRATCH_INIT)); // only called if the bit is still set
+
+    // This is called on each callee; false means callee shouldn't have
+    // no-flat-scratch-init.
+    auto CheckForNoFlatScratchInit = [&](Instruction &I) {
+      const auto &CB = cast<CallBase>(I);
+      const Function *Callee = CB.getCalledFunction();
+
+      // Callee == 0 for inline asm or indirect call with known callees.
+      // In the latter case, updateImpl() already checked the callees and we
+      // know their FLAT_SCRATCH_INIT bit is set.
+      // If function has indirect call with unknown callees, the bit is
+      // already removed in updateImpl() and execution won't reach here.
+      if (!Callee)
+        return true;
+      else
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arsenm wrote:

No else after return 

https://github.com/llvm/llvm-project/pull/94647