[SPIR-V] Set RValue for the result of bitfield extract emulation (#7200)

Otherwise, the result of bitfield extract emulation is treated as LValue
and may have an extra OpLoad generated.

Author: Junda Liu

tools/clang/lib/SPIRV/SpirvBuilder.cpp

@@ -994,6 +994,8 @@ SpirvInstruction *SpirvBuilder::createEmulatedBitFieldExtract(
     rightShift->setResultType(baseType);
   }
 
+  rightShift->setRValue(true);
+
   return rightShift;
 }
 

tools/clang/test/CodeGenSPIRV/op.struct.access.bitfield.sized.rvalue.hlsl

@@ -0,0 +1,22 @@
+// RUN: %dxc -T cs_6_2 -E main -spirv -fcgl -enable-16bit-types %s | FileCheck %s
+
+struct S1
+{
+  uint16_t a : 8;
+};
+
+S1 foo()
+{
+  return (S1)0;
+}
+
+[numthreads(1, 1, 1)]
+void main() {
+  uint16_t test = foo().a;
+// CHECK: [[ptr:%[0-9]+]] = OpAccessChain %_ptr_Function_ushort %temp_var_S1 %int_0
+// CHECK: [[raw:%[0-9]+]] = OpLoad %ushort [[ptr]]
+// CHECK: [[tmp:%[0-9]+]] = OpShiftLeftLogical %ushort [[raw]] %uint_8
+// CHECK: [[out:%[0-9]+]] = OpShiftRightLogical %ushort [[tmp]] %uint_8
+// CHECK-NOT:               OpLoad %ushort [[out]]
+// CHECK:                   OpStore %test [[out]]
+}