tint: Implement uniformity analaysis

This implements the uniformity analysis as currently described in the
WGSL specification. Uniformity issues are presented as warnings, and
will be switched to errors in a future release.

A follow-up patch will improve the error messages, which currently
just show the point at which a uniformity was detected.

In a future release, once we have obtained initial feedback from
users, uniformity issues will become errors.

Bug: tint:880
Change-Id: I7d0b3080932c786c5d50b55720fec6d19f00d356
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/88368
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Alan Baker <alanbaker@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>

docs/tint/origin-trial-changes.md

@@ -1,5 +1,12 @@
 # Tint changes during Origin Trial
 
+## Changes for M103
+
+### New features
+
+* Produce warnings for when calling barriers, textureSample, and derivative
+builtins in non-uniform control flow [tint:880](crbug.com/tint/880)
+
 ## Changes for M102
 
 ### New Features

src/tint/BUILD.gn

@@ -375,6 +375,8 @@ libtint_source_set("libtint_core_all_src") {
     "resolver/resolver_constants.cc",
     "resolver/sem_helper.cc",
     "resolver/sem_helper.h",
+    "resolver/uniformity.cc",
+    "resolver/uniformity.h",
     "resolver/validator.cc",
     "resolver/validator.h",
     "scope_stack.h",

src/tint/CMakeLists.txt

@@ -256,6 +256,8 @@ set(TINT_LIB_SRCS
   resolver/resolver.h
   resolver/sem_helper.cc
   resolver/sem_helper.h
+  resolver/uniformity.cc
+  resolver/uniformity.h
   resolver/validator.cc
   resolver/validator.h
   scope_stack.h
@@ -833,6 +835,13 @@ if(TINT_BUILD_TESTS)
     writer/text_generator_test.cc
   )
 
+  # Uniformity analysis tests depend on WGSL reader
+  if(${TINT_BUILD_WGSL_READER})
+    list(APPEND TINT_TEST_SRCS
+      resolver/uniformity_test.cc
+    )
+  endif()
+
   # Inspector tests depend on WGSL reader
   if(${TINT_BUILD_WGSL_READER})
     list(APPEND TINT_TEST_SRCS

src/tint/resolver/resolver.cc

@@ -50,6 +50,7 @@
 #include "src/tint/ast/variable_decl_statement.h"
 #include "src/tint/ast/vector.h"
 #include "src/tint/ast/workgroup_attribute.h"
+#include "src/tint/resolver/uniformity.h"
 #include "src/tint/sem/array.h"
 #include "src/tint/sem/atomic.h"
 #include "src/tint/sem/call.h"
@@ -145,6 +146,10 @@ bool Resolver::ResolveInternal() {
         return false;
     }
 
+    if (!AnalyzeUniformity(builder_, dependencies_)) {
+        // TODO(jrprice): Reject programs that fail uniformity analysis.
+    }
+
     bool result = true;
     for (auto* node : builder_->ASTNodes().Objects()) {
         if (marked_.count(node) == 0) {

src/tint/resolver/uniformity.h

@@ -0,0 +1,36 @@
+// Copyright 2022 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef SRC_TINT_RESOLVER_UNIFORMITY_H_
+#define SRC_TINT_RESOLVER_UNIFORMITY_H_
+
+// Forward declarations.
+namespace tint {
+namespace resolver {
+struct DependencyGraph;
+}  // namespace resolver
+class ProgramBuilder;
+}  // namespace tint
+
+namespace tint::resolver {
+
+/// Analyze the uniformity of a program.
+/// @param builder the program to analyze
+/// @param dependency_graph the dependency-ordered module-scope declarations
+/// @returns true if there are no uniformity issues, false otherwise
+bool AnalyzeUniformity(ProgramBuilder* builder, const resolver::DependencyGraph& dependency_graph);
+
+}  // namespace tint::resolver
+
+#endif  // SRC_TINT_RESOLVER_UNIFORMITY_H_

src/tint/scope_stack.h

@@ -71,6 +71,16 @@ class ScopeStack {
         return V{};
     }
 
+    /// Return the top scope of the stack.
+    /// @returns the top scope of the stack
+    const std::unordered_map<K, V>& Top() const { return stack_.back(); }
+
+    /// Clear the scope stack.
+    void Clear() {
+        stack_.clear();
+        stack_.push_back({});
+    }
+
   private:
     std::vector<std::unordered_map<K, V>> stack_;
 };

src/tint/scope_stack_test.cc

@@ -67,5 +67,25 @@ TEST_F(ScopeStackTest, Set) {
     EXPECT_EQ(s.Get(b), 25u);
 }
 
+TEST_F(ScopeStackTest, Clear) {
+    ScopeStack<Symbol, uint32_t> s;
+    Symbol a(1, ID());
+    Symbol b(2, ID());
+
+    EXPECT_EQ(s.Set(a, 5u), 0u);
+    EXPECT_EQ(s.Get(a), 5u);
+
+    s.Push();
+
+    EXPECT_EQ(s.Set(b, 10u), 0u);
+    EXPECT_EQ(s.Get(b), 10u);
+
+    s.Push();
+
+    s.Clear();
+    EXPECT_EQ(s.Get(a), 0u);
+    EXPECT_EQ(s.Get(b), 0u);
+}
+
 }  // namespace
 }  // namespace tint

test/tint/BUILD.gn

@@ -272,6 +272,7 @@ tint_unittests_source_set("tint_unittests_resolver_src") {
     "../../src/tint/resolver/struct_storage_class_use_test.cc",
     "../../src/tint/resolver/type_constructor_validation_test.cc",
     "../../src/tint/resolver/type_validation_test.cc",
+    "../../src/tint/resolver/uniformity_test.cc",
     "../../src/tint/resolver/validation_test.cc",
     "../../src/tint/resolver/validator_is_storeable_test.cc",
     "../../src/tint/resolver/var_let_test.cc",

test/tint/bug/dawn/947.wgsl.expected.glsl

@@ -1,3 +1,7 @@
+bug/dawn/947.wgsl:59:20 warning: 'textureSample' must only be called from uniform control flow
+    var srcColor = textureSample(myTexture, mySampler, texcoord);
+                   ^^^^^^^^^^^^^
+
 #version 310 es
 
 layout(location = 0) out vec2 texcoords_1;

test/tint/bug/dawn/947.wgsl.expected.hlsl

@@ -1,3 +1,7 @@
+bug/dawn/947.wgsl:59:20 warning: 'textureSample' must only be called from uniform control flow
+    var srcColor = textureSample(myTexture, mySampler, texcoord);
+                   ^^^^^^^^^^^^^
+
 cbuffer cbuffer_uniforms : register(b0, space0) {
   uint4 uniforms[1];
 };

test/tint/bug/dawn/947.wgsl.expected.msl

@@ -1,3 +1,7 @@
+bug/dawn/947.wgsl:59:20 warning: 'textureSample' must only be called from uniform control flow
+    var srcColor = textureSample(myTexture, mySampler, texcoord);
+                   ^^^^^^^^^^^^^
+
 #include <metal_stdlib>
 
 using namespace metal;

test/tint/bug/dawn/947.wgsl.expected.spvasm

@@ -1,3 +1,7 @@
+bug/dawn/947.wgsl:59:20 warning: 'textureSample' must only be called from uniform control flow
+    var srcColor = textureSample(myTexture, mySampler, texcoord);
+                   ^^^^^^^^^^^^^
+
 ; SPIR-V
 ; Version: 1.3
 ; Generator: Google Tint Compiler; 0

test/tint/bug/dawn/947.wgsl.expected.wgsl

@@ -1,3 +1,7 @@
+bug/dawn/947.wgsl:59:20 warning: 'textureSample' must only be called from uniform control flow
+    var srcColor = textureSample(myTexture, mySampler, texcoord);
+                   ^^^^^^^^^^^^^
+
 struct Uniforms {
   u_scale : vec2<f32>,
   u_offset : vec2<f32>,

test/tint/bug/fxc/gradient_in_varying_loop/1112.wgsl.expected.glsl

@@ -1,3 +1,7 @@
+bug/fxc/gradient_in_varying_loop/1112.wgsl:23:33 warning: 'textureSample' must only be called from uniform control flow
+        let sampleDepth : f32 = textureSample(depthTexture, Sampler, offset.xy).r;
+                                ^^^^^^^^^^^^^
+
 #version 310 es
 precision mediump float;
 

test/tint/bug/fxc/gradient_in_varying_loop/1112.wgsl.expected.hlsl

@@ -1,3 +1,7 @@
+bug/fxc/gradient_in_varying_loop/1112.wgsl:23:33 warning: 'textureSample' must only be called from uniform control flow
+        let sampleDepth : f32 = textureSample(depthTexture, Sampler, offset.xy).r;
+                                ^^^^^^^^^^^^^
+
 SamplerState tint_symbol : register(s0, space0);
 Texture2D<float4> randomTexture : register(t1, space0);
 Texture2D<float4> depthTexture : register(t2, space0);

test/tint/bug/fxc/gradient_in_varying_loop/1112.wgsl.expected.msl

@@ -1,3 +1,7 @@
+bug/fxc/gradient_in_varying_loop/1112.wgsl:23:33 warning: 'textureSample' must only be called from uniform control flow
+        let sampleDepth : f32 = textureSample(depthTexture, Sampler, offset.xy).r;
+                                ^^^^^^^^^^^^^
+
 #include <metal_stdlib>
 
 using namespace metal;

test/tint/bug/fxc/gradient_in_varying_loop/1112.wgsl.expected.spvasm

@@ -1,3 +1,7 @@
+bug/fxc/gradient_in_varying_loop/1112.wgsl:23:33 warning: 'textureSample' must only be called from uniform control flow
+        let sampleDepth : f32 = textureSample(depthTexture, Sampler, offset.xy).r;
+                                ^^^^^^^^^^^^^
+
 ; SPIR-V
 ; Version: 1.3
 ; Generator: Google Tint Compiler; 0

test/tint/bug/fxc/gradient_in_varying_loop/1112.wgsl.expected.wgsl

@@ -1,3 +1,7 @@
+bug/fxc/gradient_in_varying_loop/1112.wgsl:23:33 warning: 'textureSample' must only be called from uniform control flow
+        let sampleDepth : f32 = textureSample(depthTexture, Sampler, offset.xy).r;
+                                ^^^^^^^^^^^^^
+
 @group(0) @binding(0) var Sampler : sampler;
 
 @group(0) @binding(1) var randomTexture : texture_2d<f32>;

test/tint/bug/tint/1118.wgsl.expected.glsl

@@ -1,3 +1,7 @@
+bug/tint/1118.wgsl:64:31 warning: 'dpdx' must only be called from uniform control flow
+  normalW = normalize(-(cross(dpdx(x_62), dpdy(x_64))));
+                              ^^^^
+
 #version 310 es
 precision mediump float;
 

test/tint/bug/tint/1118.wgsl.expected.hlsl

@@ -1,3 +1,7 @@
+bug/tint/1118.wgsl:64:31 warning: 'dpdx' must only be called from uniform control flow
+  normalW = normalize(-(cross(dpdx(x_62), dpdy(x_64))));
+                              ^^^^
+
 static float fClipDistance3 = 0.0f;
 static float fClipDistance4 = 0.0f;
 cbuffer cbuffer_x_29 : register(b0, space0) {

test/tint/bug/tint/1118.wgsl.expected.msl

@@ -1,3 +1,7 @@
+bug/tint/1118.wgsl:64:31 warning: 'dpdx' must only be called from uniform control flow
+  normalW = normalize(-(cross(dpdx(x_62), dpdy(x_64))));
+                              ^^^^
+
 #include <metal_stdlib>
 
 using namespace metal;

test/tint/bug/tint/1118.wgsl.expected.spvasm

@@ -1,3 +1,7 @@
+bug/tint/1118.wgsl:64:31 warning: 'dpdx' must only be called from uniform control flow
+  normalW = normalize(-(cross(dpdx(x_62), dpdy(x_64))));
+                              ^^^^
+
 ; SPIR-V
 ; Version: 1.3
 ; Generator: Google Tint Compiler; 0

test/tint/bug/tint/1118.wgsl.expected.wgsl

@@ -1,3 +1,7 @@
+bug/tint/1118.wgsl:64:31 warning: 'dpdx' must only be called from uniform control flow
+  normalW = normalize(-(cross(dpdx(x_62), dpdy(x_64))));
+                              ^^^^
+
 struct Scene {
   vEyePosition : vec4<f32>,
 }

test/tint/bug/tint/943.spvasm.expected.glsl

@@ -1,3 +1,4 @@
+warning: parameter 'dimInner' of 'mm_matMul_i1_i1_i1_' must be uniform
 #version 310 es
 
 struct Uniforms {

test/tint/bug/tint/943.spvasm.expected.hlsl

@@ -1,3 +1,4 @@
+warning: parameter 'dimInner' of 'mm_matMul_i1_i1_i1_' must be uniform
 static int dimAOuter_1 = 0;
 cbuffer cbuffer_x_48 : register(b3, space0) {
   uint4 x_48[5];

test/tint/bug/tint/943.spvasm.expected.msl

@@ -1,3 +1,4 @@
+warning: parameter 'dimInner' of 'mm_matMul_i1_i1_i1_' must be uniform
 #include <metal_stdlib>
 
 using namespace metal;

test/tint/bug/tint/943.spvasm.expected.spvasm

@@ -1,3 +1,4 @@
+warning: parameter 'dimInner' of 'mm_matMul_i1_i1_i1_' must be uniform
 ; SPIR-V
 ; Version: 1.3
 ; Generator: Google Tint Compiler; 0

test/tint/bug/tint/943.spvasm.expected.wgsl

@@ -1,3 +1,4 @@
+warning: parameter 'dimInner' of 'mm_matMul_i1_i1_i1_' must be uniform
 struct Uniforms {
   NAN : f32,
   @size(12)

test/tint/bug/tint/948.wgsl.expected.glsl

@@ -1,3 +1,7 @@
+bug/tint/948.wgsl:146:33 warning: 'textureSampleBias' must only be called from uniform control flow
+        let x_217 : vec4<f32> = textureSampleBias(animationMapTexture, animationMapSampler, vec2<f32>(((x_208 + 0.5) / x_211), (0.125 * x_214)), 0.0);
+                                ^^^^^^^^^^^^^^^^^
+
 #version 310 es
 precision mediump float;
 

test/tint/bug/tint/948.wgsl.expected.hlsl

@@ -1,3 +1,7 @@
+bug/tint/948.wgsl:146:33 warning: 'textureSampleBias' must only be called from uniform control flow
+        let x_217 : vec4<f32> = textureSampleBias(animationMapTexture, animationMapSampler, vec2<f32>(((x_208 + 0.5) / x_211), (0.125 * x_214)), 0.0);
+                                ^^^^^^^^^^^^^^^^^
+
 cbuffer cbuffer_x_20 : register(b9, space2) {
   uint4 x_20[8];
 };

test/tint/bug/tint/948.wgsl.expected.msl

@@ -1,3 +1,7 @@
+bug/tint/948.wgsl:146:33 warning: 'textureSampleBias' must only be called from uniform control flow
+        let x_217 : vec4<f32> = textureSampleBias(animationMapTexture, animationMapSampler, vec2<f32>(((x_208 + 0.5) / x_211), (0.125 * x_214)), 0.0);
+                                ^^^^^^^^^^^^^^^^^
+
 #include <metal_stdlib>
 
 using namespace metal;

test/tint/bug/tint/948.wgsl.expected.spvasm

@@ -1,3 +1,7 @@
+bug/tint/948.wgsl:146:33 warning: 'textureSampleBias' must only be called from uniform control flow
+        let x_217 : vec4<f32> = textureSampleBias(animationMapTexture, animationMapSampler, vec2<f32>(((x_208 + 0.5) / x_211), (0.125 * x_214)), 0.0);
+                                ^^^^^^^^^^^^^^^^^
+
 ; SPIR-V
 ; Version: 1.3
 ; Generator: Google Tint Compiler; 0

test/tint/bug/tint/948.wgsl.expected.wgsl

@@ -1,3 +1,7 @@
+bug/tint/948.wgsl:146:33 warning: 'textureSampleBias' must only be called from uniform control flow
+        let x_217 : vec4<f32> = textureSampleBias(animationMapTexture, animationMapSampler, vec2<f32>(((x_208 + 0.5) / x_211), (0.125 * x_214)), 0.0);
+                                ^^^^^^^^^^^^^^^^^
+
 struct LeftOver {
   time : f32,
   @size(12)

test/tint/bug/tint/949.wgsl.expected.glsl

@@ -1,3 +1,7 @@
+bug/tint/949.wgsl:326:29 warning: 'textureSample' must only be called from uniform control flow
+    let x_397 : vec4<f32> = textureSample(TextureSamplerTexture, TextureSamplerSampler, (x_394 + x_395));
+                            ^^^^^^^^^^^^^
+
 #version 310 es
 precision mediump float;
 

test/tint/bug/tint/949.wgsl.expected.hlsl

@@ -1,3 +1,7 @@
+bug/tint/949.wgsl:326:29 warning: 'textureSample' must only be called from uniform control flow
+    let x_397 : vec4<f32> = textureSample(TextureSamplerTexture, TextureSamplerSampler, (x_394 + x_395));
+                            ^^^^^^^^^^^^^
+
 struct lightingInfo {
   float3 diffuse;
   float3 specular;

test/tint/bug/tint/949.wgsl.expected.msl

@@ -1,3 +1,7 @@
+bug/tint/949.wgsl:326:29 warning: 'textureSample' must only be called from uniform control flow
+    let x_397 : vec4<f32> = textureSample(TextureSamplerTexture, TextureSamplerSampler, (x_394 + x_395));
+                            ^^^^^^^^^^^^^
+
 #include <metal_stdlib>
 
 using namespace metal;

test/tint/bug/tint/949.wgsl.expected.spvasm

@@ -1,3 +1,7 @@
+bug/tint/949.wgsl:326:29 warning: 'textureSample' must only be called from uniform control flow
+    let x_397 : vec4<f32> = textureSample(TextureSamplerTexture, TextureSamplerSampler, (x_394 + x_395));
+                            ^^^^^^^^^^^^^
+
 ; SPIR-V
 ; Version: 1.3
 ; Generator: Google Tint Compiler; 0

test/tint/bug/tint/949.wgsl.expected.wgsl

@@ -1,3 +1,7 @@
+bug/tint/949.wgsl:326:29 warning: 'textureSample' must only be called from uniform control flow
+    let x_397 : vec4<f32> = textureSample(TextureSamplerTexture, TextureSamplerSampler, (x_394 + x_395));
+                            ^^^^^^^^^^^^^
+
 struct lightingInfo {
   diffuse : vec3<f32>,
   specular : vec3<f32>,