Implement textureGather, textureGatherCompare

All writers implemented, along with resolving and validation.

TODO: SPIR-V Reader.

Bug: tint:1330
Change-Id: I8ba2f6023749474f80efb8a5422ac187e6c73a69
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/71820
Reviewed-by: David Neto <dneto@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Kokoro: Ben Clayton <bclayton@google.com>

src/sem/intrinsic.cc

@@ -50,6 +50,8 @@ bool IsFloatClassificationIntrinsic(IntrinsicType i) {
 
 bool IsTextureIntrinsic(IntrinsicType i) {
   return IsImageQueryIntrinsic(i) || i == IntrinsicType::kTextureLoad ||
+         i == IntrinsicType::kTextureGather ||
+         i == IntrinsicType::kTextureGatherCompare ||
          i == IntrinsicType::kTextureSample ||
          i == IntrinsicType::kTextureSampleLevel ||
          i == IntrinsicType::kTextureSampleBias ||

src/sem/intrinsic_type.cc

@@ -261,6 +261,12 @@ IntrinsicType ParseIntrinsicType(const std::string& name) {
   if (name == "textureDimensions") {
     return IntrinsicType::kTextureDimensions;
   }
+  if (name == "textureGather") {
+    return IntrinsicType::kTextureGather;
+  }
+  if (name == "textureGatherCompare") {
+    return IntrinsicType::kTextureGatherCompare;
+  }
   if (name == "textureNumLayers") {
     return IntrinsicType::kTextureNumLayers;
   }
@@ -488,6 +494,10 @@ const char* str(IntrinsicType i) {
       return "workgroupBarrier";
     case IntrinsicType::kTextureDimensions:
       return "textureDimensions";
+    case IntrinsicType::kTextureGather:
+      return "textureGather";
+    case IntrinsicType::kTextureGatherCompare:
+      return "textureGatherCompare";
     case IntrinsicType::kTextureNumLayers:
       return "textureNumLayers";
     case IntrinsicType::kTextureNumLevels:

src/sem/intrinsic_type.h

@@ -111,6 +111,8 @@ enum class IntrinsicType {
   kUnpack4x8unorm,
   kWorkgroupBarrier,
   kTextureDimensions,
+  kTextureGather,
+  kTextureGatherCompare,
   kTextureNumLayers,
   kTextureNumLevels,
   kTextureNumSamples,

src/sem/parameter_usage.cc

@@ -35,6 +35,8 @@ const char* str(ParameterUsage usage) {
       return "array_index";
     case ParameterUsage::kBias:
       return "bias";
+    case ParameterUsage::kComponent:
+      return "component";
     case ParameterUsage::kCoords:
       return "coords";
     case ParameterUsage::kDdx:

src/sem/parameter_usage.h

@@ -34,6 +34,7 @@ enum class ParameterUsage {
   kNone = -1,
   kArrayIndex,
   kBias,
+  kComponent,
   kCoords,
   kDdx,
   kDdy,