Allow removal of trivially dead convergent marker

include/dxc/DXIL/DxilUtil.h

@@ -152,6 +152,9 @@ namespace dxilutil {
 
   void ReplaceRawBufferLoad64Bit(llvm::Function *F, llvm::Type *EltTy, hlsl::OP *hlslOP);
   void ReplaceRawBufferStore64Bit(llvm::Function *F, llvm::Type *ETy, hlsl::OP *hlslOP);
+
+  bool IsConvergentMarker(llvm::Value *V);
+  llvm::Value *GetConvergentSource(llvm::Value *V);
 }
 
 }

lib/DXIL/DxilUtil.cpp

@@ -14,6 +14,7 @@
 #include "dxc/DXIL/DxilUtil.h"
 #include "dxc/DXIL/DxilModule.h"
 #include "dxc/DXIL/DxilOperations.h"
+#include "dxc/HLSL/DxilConvergentName.h"
 #include "dxc/Support/Global.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/Twine.h"
@@ -1171,6 +1172,26 @@ void ReplaceRawBufferStore64Bit(llvm::Function *F, llvm::Type *ETy, hlsl::OP *hl
   }
 }
 
+bool IsConvergentMarker(const char *Name) {
+  StringRef RName = Name;
+  return RName.startswith(kConvergentFunctionPrefix);
+}
+
+bool IsConvergentMarker(const Function *F) {
+  return F && F->getName().startswith(kConvergentFunctionPrefix);
+}
+
+bool IsConvergentMarker(Value *V) {
+  CallInst *CI = dyn_cast<CallInst>(V);
+  if (!CI)
+    return false;
+  return IsConvergentMarker(CI->getCalledFunction());
+}
+
+Value *GetConvergentSource(Value *V) {
+  return cast<CallInst>(V)->getOperand(0);
+}
+
 }
 }
 

lib/HLSL/DxilConvergent.cpp

@@ -22,24 +22,13 @@
 #include "dxc/HLSL/DxilGenerationPass.h"
 #include "dxc/HLSL/HLOperations.h"
 #include "dxc/HLSL/HLModule.h"
-#include "dxc/HLSL/DxilConvergent.h"
 #include "dxc/HlslIntrinsicOp.h"
 #include "dxc/HLSL/DxilConvergentName.h"
 
 using namespace llvm;
 using namespace hlsl;
 
-bool hlsl::IsConvergentMarker(Value *V) {
-  CallInst *CI = dyn_cast<CallInst>(V);
-  if (!CI)
-    return false;
-  Function *F = CI->getCalledFunction();
-  return F->getName().startswith(kConvergentFunctionPrefix);
-}
 
-Value *hlsl::GetConvergentSource(Value *V) {
-  return cast<CallInst>(V)->getOperand(0);
-}
 
 ///////////////////////////////////////////////////////////////////////////////
 // DxilConvergent.

lib/HLSL/HLOperationLower.cpp

@@ -25,7 +25,6 @@
 #include "dxc/HLSL/HLOperationLowerExtension.h"
 #include "dxc/HLSL/HLOperations.h"
 #include "dxc/HlslIntrinsicOp.h"
-#include "dxc/HLSL/DxilConvergent.h"
 #include "dxc/DXIL/DxilResourceProperties.h"
 
 #include "llvm/IR/GetElementPtrTypeIterator.h"
@@ -844,8 +843,8 @@ Value *FindScalarSource(Value *src, unsigned vecIdx = 0) {
         vecIdx = (unsigned)cast<ConstantInt>(EE->getIndexOperand())
           ->getUniqueInteger().getLimitedValue();
         src = EE->getVectorOperand();
-      } else if (hlsl::IsConvergentMarker(src)) {
-        src = hlsl::GetConvergentSource(src);
+      } else if (hlsl::dxilutil::IsConvergentMarker(src)) {
+        src = hlsl::dxilutil::GetConvergentSource(src);
       } else {
         break;  // Found it.
       }

lib/Transforms/Utils/Local.cpp

@@ -46,6 +46,7 @@
 #include "llvm/Support/raw_ostream.h"
 
 #include "dxc/DXIL/DxilMetadataHelper.h" // HLSL Change - combine dxil metadata.
+#include "dxc/DXIL/DxilUtil.h" // HLSL Change - special handling of convergent marker
 using namespace llvm;
 
 #define DEBUG_TYPE "local"
@@ -331,6 +332,10 @@ bool llvm::isInstructionTriviallyDead(Instruction *I,
     if (Constant *C = dyn_cast<Constant>(CI->getArgOperand(0)))
       return C->isNullValue() || isa<UndefValue>(C);
 
+  // HLSL change - don't force unused convergenet markers to stay
+  if (CallInst *CI = dyn_cast<CallInst>(I))
+    if (hlsl::dxilutil::IsConvergentMarker(CI)) return true;
+
   return false;
 }
 

tools/clang/test/HLSLFileCheck/passes/llvm/dce/remove_convergent_marker.hlsl

@@ -0,0 +1,20 @@
+// RUN: %dxc /T ps_6_0  %s | FileCheck %s
+
+// Tests that a convergent marker added by a derivative call
+// is removed in time to let the rest of the dead code be removed
+
+
+// Since everything is ignored, there should be no conditionals
+// and just a single return void
+
+// CHECK: void @main
+// CHECK-NOT: br
+// CHECK: storeOutput
+// CHECK: ret void
+
+float main(float d : DEPTH0) : SV_Target {
+    if (d > 0)
+      d = max(d, 3.0);
+    ddx(d+1);
+    return 0.0;
+}