[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, 4 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CodeGenFunction.h b/clang/lib/CodeGen/CodeGenFunction.h
index b38c009..ff42113 100644
--- a/clang/lib/CodeGen/CodeGenFunction.h
+++ b/clang/lib/CodeGen/CodeGenFunction.h
@@ -615,6 +615,10 @@ public:
   /// True if the current statement has noconvergent attribute.
   bool InNoConvergentAttributedStmt = false;
 
+  /// HLSL Branch attribute.
+  HLSLControlFlowHintAttr::Spelling HLSLControlFlowAttr =
+      HLSLControlFlowHintAttr::SpellingNotCalculated;
+
   // The CallExpr within the current statement that the musttail attribute
   // applies to.  nullptr if there is no 'musttail' on the current statement.
   const CallExpr *MustTailCall = nullptr;