[HLSL] Adding Flatten and Branch if attributes (#116331)

- adding Flatten and Branch to if stmt.
- adding dxil control flow hint metadata generation
- modifing spirv OpSelectMerge to account for the specific attributes.

Closes #70112

---------

Co-authored-by: Joao Saffran <jderezende@microsoft.com>
Co-authored-by: joaosaffran <joao.saffran@microsoft.com>

1 files changed, 21 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index af58fa6..56c56f5 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -40,6 +40,7 @@
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/Dominators.h"
 #include "llvm/IR/FPEnv.h"
+#include "llvm/IR/Instruction.h"
 #include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/Intrinsics.h"
 #include "llvm/IR/MDBuilder.h"
@@ -2083,7 +2084,26 @@ void CodeGenFunction::EmitBranchOnBoolExpr(
     Weights = createProfileWeights(TrueCount, CurrentCount - TrueCount);
   }
 
-  Builder.CreateCondBr(CondV, TrueBlock, FalseBlock, Weights, Unpredictable);
+  llvm::Instruction *BrInst = Builder.CreateCondBr(CondV, TrueBlock, FalseBlock,
+                                                   Weights, Unpredictable);
+  switch (HLSLControlFlowAttr) {
+  case HLSLControlFlowHintAttr::Microsoft_branch:
+  case HLSLControlFlowHintAttr::Microsoft_flatten: {
+    llvm::MDBuilder MDHelper(CGM.getLLVMContext());
+
+    llvm::ConstantInt *BranchHintConstant =
+        HLSLControlFlowAttr ==
+                HLSLControlFlowHintAttr::Spelling::Microsoft_branch
+            ? llvm::ConstantInt::get(CGM.Int32Ty, 1)
+            : llvm::ConstantInt::get(CGM.Int32Ty, 2);
+
+    SmallVector<llvm::Metadata *, 2> Vals(
+        {MDHelper.createString("hlsl.controlflow.hint"),
+         MDHelper.createConstant(BranchHintConstant)});
+    BrInst->setMetadata("hlsl.controlflow.hint",
+                        llvm::MDNode::get(CGM.getLLVMContext(), Vals));
+  } break;
+  }
 }
 
 /// ErrorUnsupported - Print out an error that codegen doesn't support the