Avoid capability checks on ID values. They are not literals

Works around issue 248 by weakening the test:
KhronosGroup#248

The validator should try to track (32-bit) constant values, and then
for capability checks on IDs, check the referenced value, not the
raw ID number.

source/validate_instruction.cpp

@@ -35,6 +35,7 @@
 
 #include "diagnostic.h"
 #include "opcode.h"
+#include "operand.h"
 #include "spirv_definition.h"
 #include "val/Function.h"
 #include "val/ValidationState.h"
@@ -109,6 +110,10 @@ spv_result_t CapCheck(ValidationState_t& _,
           }
         }
       }
+    } else if (spvIsIdType(operand.type)) {
+      // TODO(dneto): Check the value referenced by this Id, if we can compute
+      // it.  For now, just punt, to fix issue 248:
+      // https://github.com/KhronosGroup/SPIRV-Tools/issues/248
     } else {
       // Check the operand word as a whole.
       const auto caps = RequiredCapabilities(_.grammar(), operand.type, word);

test/Validate.Capability.cpp

@@ -1153,4 +1153,39 @@ TEST_P(ValidateCapabilityV11, Capability) {
       << test_code;
 }
 
+TEST_F(ValidateCapability, SemanticsIdIsAnIdNotALiteral) {
+  // From https://github.com/KhronosGroup/SPIRV-Tools/issues/248
+  // The validator was interpreting the memory semantics ID number
+  // as the value to be checked rather than an ID that references
+  // another value to be checked.
+  // In this case a raw ID of 64 was mistaken to mean a literal
+  // semantic value of UniformMemory, which would require the Shader
+  // capability.
+  const char str[] = R"(
+OpCapability Kernel
+OpMemoryModel Logical OpenCL
+
+;  %i32 has ID 1
+%i32    = OpTypeInt 32 1
+%tf     = OpTypeFunction %i32
+%pi32   = OpTypePointer CrossWorkgroup %i32
+%var    = OpVariable %pi32 CrossWorkgroup
+%c      = OpConstant %i32 100
+%scope  = OpConstant %i32 1 ; Device scope
+
+; Fake an instruction with 64 as the result id.
+; !64 = OpConstantNull %i32
+!0x3002e !1 !64
+
+%f = OpFunction %i32 None %tf
+%l = OpLabel
+%result = OpAtomicIAdd %i32 %var %scope !64 %c
+OpReturnValue %result
+OpFunctionEnd
+)";
+
+  CompileSuccessfully(str);
+  ASSERT_EQ(SPV_SUCCESS, ValidateInstructions());
+}
+
 }  // namespace anonymous