Transform textureLoad calls for texture_external

Adds a transform that adds an additional 'level' parameter to textureLoad calls
when used with a texture_external. Adds a test for the textureLoad
transform. Additionally adds a test for calls to textureDimensions with
a texture_external.

Bug: dawn:728
Change-Id: I613ce8185e9a4c49529fd8e48323e586c95dde04
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/50420
Commit-Queue: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>

src/transform/external_texture_transform.cc

@@ -13,7 +13,10 @@
 // limitations under the License.
 
 #include "src/transform/external_texture_transform.h"
+
 #include "src/program_builder.h"
+#include "src/sem/call.h"
+#include "src/sem/variable.h"
 
 namespace tint {
 namespace transform {
@@ -24,6 +27,57 @@ ExternalTextureTransform::~ExternalTextureTransform() = default;
 Output ExternalTextureTransform::Run(const Program* in, const DataMap&) {
   ProgramBuilder out;
   CloneContext ctx(&out, in);
+  auto& sem = ctx.src->Sem();
+
+  // Within this transform, usages of texture_external are replaced with a
+  // texture_2d<f32>, which will allow us perform operations on a
+  // texture_external without maintaining texture_external-specific code
+  // generation paths in the backends.
+
+  // When replacing instances of texture_external with texture_2d<f32> we must
+  // also modify calls to the texture_external overload of textureLoad, which
+  // unlike its texture_2d<f32> overload does not require a level parameter.
+  // To do this we identify calls to textureLoad that use texture_external as
+  // the first parameter and add a parameter for the level (which is always 0).
+
+  // Scan the AST nodes for calls to textureLoad.
+  for (auto* node : ctx.src->ASTNodes().Objects()) {
+    if (auto* call_expr = node->As<ast::CallExpression>()) {
+      if (auto* intrinsic =
+              sem.Get(call_expr)->Target()->As<sem::Intrinsic>()) {
+        if (intrinsic->Type() == sem::IntrinsicType::kTextureLoad) {
+          // When a textureLoad has been identified, check if the first
+          // parameter is an external texture.
+          if (auto* var =
+                  sem.Get(call_expr->params()[0])->As<sem::VariableUser>()) {
+            if (var->Variable()->Type()->Is<sem::ExternalTexture>()) {
+              if (call_expr->params().size() != 2) {
+                TINT_ICE(ctx.dst->Diagnostics())
+                    << "expected TextureLoad call with a texture_external to "
+                       "have 2 parameters, found "
+                    << call_expr->params().size() << " parameters";
+              }
+              // Replace the textureLoad call with another that has the same
+              // parameters in addition to a signed integer literal for the
+              // level parameter.
+              auto* exp = ctx.Clone(call_expr->func());
+
+              auto* externalTextureParam = ctx.Clone(call_expr->params()[0]);
+              auto* coordsParam = ctx.Clone(call_expr->params()[1]);
+              // Level is always 0 for an external texture.
+              auto* levelParam = ctx.dst->Expr(0);
+
+              ast::ExpressionList params = {externalTextureParam, coordsParam,
+                                            levelParam};
+
+              auto* newCall = ctx.dst->create<ast::CallExpression>(exp, params);
+              ctx.Replace(call_expr, newCall);
+            }
+          }
+        }
+      }
+    }
+  }
 
   // Scan the AST nodes for external texture declarations.
   for (auto* node : ctx.src->ASTNodes().Objects()) {

src/transform/external_texture_transform_test.cc

@@ -22,7 +22,7 @@ namespace {
 
 using ExternalTextureTransformTest = TransformTest;
 
-TEST_F(ExternalTextureTransformTest, SinglePlane) {
+TEST_F(ExternalTextureTransformTest, SampleSinglePlane) {
   auto* src = R"(
 [[group(0), binding(0)]] var s : sampler;
 
@@ -50,6 +50,58 @@ fn main([[builtin(position)]] coord : vec4<f32>) -> [[location(0)]] vec4<f32> {
   EXPECT_EQ(expect, str(got));
 }
 
+TEST_F(ExternalTextureTransformTest, LoadSinglePlane) {
+  auto* src = R"(
+[[group(0), binding(0)]] var t : texture_external;
+
+[[stage(fragment)]]
+fn main([[builtin(position)]] coord : vec4<f32>) -> [[location(0)]] vec4<f32> {
+  return textureLoad(t, vec2<i32>(1, 1));
+}
+)";
+
+  auto* expect = R"(
+[[group(0), binding(0)]] var t : texture_2d<f32>;
+
+[[stage(fragment)]]
+fn main([[builtin(position)]] coord : vec4<f32>) -> [[location(0)]] vec4<f32> {
+  return textureLoad(t, vec2<i32>(1, 1), 0);
+}
+)";
+
+  auto got = Run<ExternalTextureTransform>(src);
+
+  EXPECT_EQ(expect, str(got));
+}
+
+TEST_F(ExternalTextureTransformTest, DimensionsSinglePlane) {
+  auto* src = R"(
+[[group(0), binding(0)]] var t : texture_external;
+
+[[stage(fragment)]]
+fn main([[builtin(position)]] coord : vec4<f32>) -> [[location(0)]] vec4<f32> {
+  var dim : vec2<i32>;
+  dim = textureDimensions(t);
+  return vec4<f32>(0.0, 0.0, 0.0, 0.0);
+}
+)";
+
+  auto* expect = R"(
+[[group(0), binding(0)]] var t : texture_2d<f32>;
+
+[[stage(fragment)]]
+fn main([[builtin(position)]] coord : vec4<f32>) -> [[location(0)]] vec4<f32> {
+  var dim : vec2<i32>;
+  dim = textureDimensions(t);
+  return vec4<f32>(0.0, 0.0, 0.0, 0.0);
+}
+)";
+
+  auto got = Run<ExternalTextureTransform>(src);
+
+  EXPECT_EQ(expect, str(got));
+}
+
 }  // namespace
 }  // namespace transform
 }  // namespace tint