Don't generate lshr for cb array indexing. (#812)

lib/HLSL/HLOperationLower.cpp

@@ -5315,8 +5315,7 @@ void TranslateCBGepLegacy(GetElementPtrInst *GEP, Value *handle,
         unsigned idxInc = tempOffset >> 4;
         legacyIndex = Builder.CreateAdd(legacyIndex, hlslOP->GetU32Const(idxInc));
       } else {
-        Value *tempOffset = Builder.CreateMul(idx, hlslOP->GetU32Const(size));
-        Value *idxInc = Builder.CreateLShr(tempOffset, 4);
+        Value *idxInc = Builder.CreateMul(idx, hlslOP->GetU32Const(size>>4));
         legacyIndex = Builder.CreateAdd(legacyIndex, idxInc);
       }
 
@@ -5366,8 +5365,7 @@ void TranslateCBGepLegacy(GetElementPtrInst *GEP, Value *handle,
         unsigned idxInc = tempOffset >> 4;
         legacyIndex = Builder.CreateAdd(legacyIndex, hlslOP->GetU32Const(idxInc));
       } else {
-        Value *tempOffset = Builder.CreateMul(idx, hlslOP->GetU32Const(size));
-        Value *idxInc = Builder.CreateLShr(tempOffset, 4);
+        Value *idxInc = Builder.CreateMul(idx, hlslOP->GetU32Const(size>>4));
         legacyIndex = Builder.CreateAdd(legacyIndex, idxInc);
       }
 

tools/clang/test/CodeGenHLSL/quick-test/cb_array.hlsl

@@ -0,0 +1,14 @@
+// RUN: %dxc -E main -T ps_6_0 %s | FileCheck %s
+
+// Make sure no lshr created for cbuffer array.
+// CHECK-NOT: lshr
+// CHECK:[[ID:[^ ]+]] = call i32 @dx.op.loadInput.i32
+// CHECK:[[ADD:[^ ]+]] = add nsw i32 [[ID]], 2
+// CHECK:call %dx.types.CBufRet.f32 @dx.op.cbufferLoadLegacy.f32(i32 59, %dx.types.Handle %"$Globals_buffer", i32 [[ADD]])
+
+
+float A[6] : register(b0);
+float main(int i : A) : SV_TARGET
+{
+  return A[i] + A[i+1] + A[i+2] ;
+}