Use vector size from vector type when dynamic indexing cb vector. (#3530)

lib/HLSL/HLOperationLower.cpp

@@ -6648,12 +6648,8 @@ void TranslateCBGepLegacy(GetElementPtrInst *GEP, Value *handle,
         }
       } else {
         Type *EltTy = GEPIt->getVectorElementType();
-        unsigned size = DL.getTypeSizeInBits(EltTy);
-        unsigned vecSize = 4;
-        if (size == 64)
-          vecSize = 2;
-        else if (size == 16)
-          vecSize = 8;
+        unsigned vecSize = GEPIt->getVectorNumElements();
+
         // Load the whole register.
         Value *newLd = GenerateCBLoadLegacy(handle, legacyIndex,
                                      /*channelOffset*/ 0, EltTy,

tools/clang/test/HLSLFileCheck/hlsl/objects/CbufferLegacy/double4_indexing.hlsl

@@ -0,0 +1,12 @@
+// RUN: %dxc -E main -T ps_6_0 %s | FileCheck %s
+
+// Make sure only 2 cbufferLoadLegacy.
+// CHECK:call %dx.types.CBufRet.f64 @dx.op.cbufferLoadLegacy.f64(i32 59, %dx.types.Handle %{{.*}}, i32 0)
+// CHECK:call %dx.types.CBufRet.f64 @dx.op.cbufferLoadLegacy.f64(i32 59, %dx.types.Handle %{{.*}}, i32 1)
+// CHECK-NOT:call %dx.types.CBufRet.f64
+
+double4 g;
+
+float main(int2 i:I) : SV_Target {
+  return g[i.x]+g[i.y];
+}