[clang] [llvm] [clang][HLSL][SPRI-V] Add convergence intrinsics (PR #80680)

[Matt Arsenault via cfe-commits]

Nathan =?utf-8?q?Gauër?= <brioche at google.com>,
Nathan =?utf-8?q?Gauër?= <brioche at google.com>
Message-ID:
In-Reply-To: <llvm.org/llvm/llvm-project/pull/80680 at github.com>


================
@@ -1130,8 +1130,96 @@ struct BitTest {
 
   static BitTest decodeBitTestBuiltin(unsigned BuiltinID);
 };
+
+// Returns the first convergence entry/loop/anchor instruction found in |BB|.
+// std::nullopt otherwise.
+std::optional<llvm::IntrinsicInst *> getConvergenceToken(llvm::BasicBlock *BB) {
+  for (auto &I : *BB) {
+    auto *II = dyn_cast<llvm::IntrinsicInst>(&I);
+    if (II && isConvergenceControlIntrinsic(II->getIntrinsicID()))
+      return II;
+  }
+  return std::nullopt;
+}
+
 } // namespace
 
+llvm::CallBase *
+CodeGenFunction::AddConvergenceControlAttr(llvm::CallBase *Input,
+                                           llvm::Value *ParentToken) {
+  llvm::Value *bundleArgs[] = {ParentToken};
+  llvm::OperandBundleDef OB("convergencectrl", bundleArgs);
+  auto Output = llvm::CallBase::addOperandBundle(
+      Input, llvm::LLVMContext::OB_convergencectrl, OB, Input);
+  Input->replaceAllUsesWith(Output);
+  Input->eraseFromParent();
+  return Output;
+}
+
+llvm::IntrinsicInst *
+CodeGenFunction::EmitConvergenceLoop(llvm::BasicBlock *BB,
+                                     llvm::Value *ParentToken) {
+  CGBuilderTy::InsertPoint IP = Builder.saveIP();
+  Builder.SetInsertPoint(&BB->front());
+  auto CB = Builder.CreateIntrinsic(
+      llvm::Intrinsic::experimental_convergence_loop, {}, {});
+  Builder.restoreIP(IP);
+
+  auto I = AddConvergenceControlAttr(CB, ParentToken);
+  // Controlled convergence is incompatible with uncontrolled convergence.
+  // Removing any old attributes.
+  I->setNotConvergent();
----------------
arsenm wrote:

Don't understand this. I thought it was a verifier error to be not-convergent and have a convergence token.

This won't actually do anything for an intrinsic. Because convergent is broken/backwards, you can't locally override it at a callsite and you can't remove the convergent from the underlying declaration 

https://github.com/llvm/llvm-project/pull/80680