fix(naga): Evaluate compound assignment LHS before RHS (#9181)

Author: andyleiserson

CHANGELOG.md

@@ -209,6 +209,7 @@ depth_stencil: Some(wgpu::DepthStencilState::stencil(
 - Naga now detects bitwise shifts by a constant exceeding the operand bit width at compile time, and disallows scalar-by-vector and vector-by-scalar shifts in constant evaluation. By @andyleiserson in [#8907](https://github.com/gfx-rs/wgpu/pull/8907).
 - Naga uses wrapping arithmetic when evaluating dot products on concrete integer types (`u32` and `i32`). By @BKDaugherty in [#9142](https://github.com/gfx-rs/wgpu/pull/9142).
 - Disallow negation of a matrix in WGSL. By @andyleiserson in [#9157](https://github.com/gfx-rs/wgpu/pull/9157).
+- Fix evaluation order of compound assignment (e.g. `+=`) LHS and RHS. By @andyleiserson in [#9181](https://github.com/gfx-rs/wgpu/pull/9181).
 
 #### Validation
 

cts_runner/test.lst

@@ -324,6 +324,7 @@ webgpu:shader,execution,flow_control,return:*
 // Many other vertex_buffer_access subtests also passing, but there are too many to enumerate.
 // Fails on Metal in CI only, not when running locally.
 fails-if(metal) webgpu:shader,execution,robust_access_vertex:vertex_buffer_access:indexed=true;indirect=false;drawCallTestParameter="baseVertex";type="float32x4";additionalBuffers=4;partialLastNumber=false;offsetVertexBuffer=true
+webgpu:shader,execution,statement,compound:*
 
 webgpu:shader,validation,const_assert,const_assert:*
 webgpu:shader,validation,decl,assignment_statement:*

naga/src/front/wgsl/lower/mod.rs

@@ -2153,6 +2153,13 @@ impl<'source, 'temp> Lowerer<'source, 'temp> {
                         .pointer_automatically_convertible_scalar(&ectx.module.types),
                 };
 
+                // Need to emit the LHS _before_ the RHS so that it is evaluated first.
+                let op_assign = if let Some(op) = op {
+                    Some((op, ectx.apply_load_rule(target)?))
+                } else {
+                    None
+                };
+
                 let value = self.expression_for_abstract(value, &mut ectx)?;
                 let mut value = match target_scalar {
                     Some(target_scalar) => ectx.try_automatic_conversion_for_leaf_scalar(
@@ -2163,9 +2170,8 @@ impl<'source, 'temp> Lowerer<'source, 'temp> {
                     None => value,
                 };
 
-                let value = match op {
-                    Some(op) => {
-                        let mut left = ectx.apply_load_rule(target)?;
+                let value = match op_assign {
+                    Some((op, mut left)) => {
                         ectx.binary_op_splat(op, &mut left, &mut value)?;
                         ectx.append_expression(
                             ir::Expression::Binary {

naga/tests/out/glsl/wgsl-break-if.main.Compute.glsl

@@ -68,8 +68,8 @@ void breakIfSeparateVariable() {
             }
         }
         loop_init_3 = false;
-        uint _e3 = counter;
-        counter = (_e3 + 1u);
+        uint _e2 = counter;
+        counter = (_e2 + 1u);
     }
     return;
 }

naga/tests/out/glsl/wgsl-image.texture_sample.Fragment.glsl

@@ -14,75 +14,75 @@ void main() {
     vec2 _e1 = vec2(0.5);
     vec3 _e3 = vec3(0.5);
     ivec2 _e6 = ivec2(3, 1);
-    vec4 _e11 = texture(_group_0_binding_0_fs, 0.5);
-    vec4 _e12 = a;
-    a = (_e12 + _e11);
-    vec4 _e16 = texture(_group_0_binding_1_fs, vec2(_e1));
-    vec4 _e17 = a;
-    a = (_e17 + _e16);
-    vec4 _e24 = textureOffset(_group_0_binding_1_fs, vec2(_e1), ivec2(3, 1));
-    vec4 _e25 = a;
-    a = (_e25 + _e24);
-    vec4 _e29 = textureLod(_group_0_binding_1_fs, vec2(_e1), 2.3);
-    vec4 _e30 = a;
-    a = (_e30 + _e29);
-    vec4 _e34 = textureLodOffset(_group_0_binding_1_fs, vec2(_e1), 2.3, ivec2(3, 1));
-    vec4 _e35 = a;
-    a = (_e35 + _e34);
-    vec4 _e40 = textureOffset(_group_0_binding_1_fs, vec2(_e1), ivec2(3, 1), 2.0);
-    vec4 _e41 = a;
-    a = (_e41 + _e40);
-    vec4 _e45 = textureLod(_group_0_binding_1_fs, vec2(_e1), 0.0);
-    vec4 _e46 = a;
-    a = (_e46 + _e45);
-    vec4 _e51 = texture(_group_0_binding_4_fs, vec3(_e1, 0u));
-    vec4 _e52 = a;
-    a = (_e52 + _e51);
-    vec4 _e57 = textureOffset(_group_0_binding_4_fs, vec3(_e1, 0u), ivec2(3, 1));
-    vec4 _e58 = a;
-    a = (_e58 + _e57);
-    vec4 _e63 = textureLod(_group_0_binding_4_fs, vec3(_e1, 0u), 2.3);
-    vec4 _e64 = a;
-    a = (_e64 + _e63);
-    vec4 _e69 = textureLodOffset(_group_0_binding_4_fs, vec3(_e1, 0u), 2.3, ivec2(3, 1));
-    vec4 _e70 = a;
-    a = (_e70 + _e69);
-    vec4 _e76 = textureOffset(_group_0_binding_4_fs, vec3(_e1, 0u), ivec2(3, 1), 2.0);
-    vec4 _e77 = a;
-    a = (_e77 + _e76);
-    vec4 _e82 = texture(_group_0_binding_4_fs, vec3(_e1, 0));
-    vec4 _e83 = a;
-    a = (_e83 + _e82);
-    vec4 _e88 = textureOffset(_group_0_binding_4_fs, vec3(_e1, 0), ivec2(3, 1));
-    vec4 _e89 = a;
-    a = (_e89 + _e88);
-    vec4 _e94 = textureLod(_group_0_binding_4_fs, vec3(_e1, 0), 2.3);
-    vec4 _e95 = a;
-    a = (_e95 + _e94);
-    vec4 _e100 = textureLodOffset(_group_0_binding_4_fs, vec3(_e1, 0), 2.3, ivec2(3, 1));
-    vec4 _e101 = a;
-    a = (_e101 + _e100);
-    vec4 _e107 = textureOffset(_group_0_binding_4_fs, vec3(_e1, 0), ivec2(3, 1), 2.0);
-    vec4 _e108 = a;
-    a = (_e108 + _e107);
-    vec4 _e113 = texture(_group_0_binding_6_fs, vec4(_e3, 0u));
-    vec4 _e114 = a;
-    a = (_e114 + _e113);
-    vec4 _e119 = textureLod(_group_0_binding_6_fs, vec4(_e3, 0u), 2.3);
-    vec4 _e120 = a;
-    a = (_e120 + _e119);
-    vec4 _e126 = texture(_group_0_binding_6_fs, vec4(_e3, 0u), 2.0);
-    vec4 _e127 = a;
-    a = (_e127 + _e126);
-    vec4 _e132 = texture(_group_0_binding_6_fs, vec4(_e3, 0));
-    vec4 _e133 = a;
-    a = (_e133 + _e132);
-    vec4 _e138 = textureLod(_group_0_binding_6_fs, vec4(_e3, 0), 2.3);
-    vec4 _e139 = a;
-    a = (_e139 + _e138);
-    vec4 _e145 = texture(_group_0_binding_6_fs, vec4(_e3, 0), 2.0);
-    vec4 _e146 = a;
-    a = (_e146 + _e145);
+    vec4 _e9 = a;
+    vec4 _e12 = texture(_group_0_binding_0_fs, 0.5);
+    a = (_e9 + _e12);
+    vec4 _e14 = a;
+    vec4 _e17 = texture(_group_0_binding_1_fs, vec2(_e1));
+    a = (_e14 + _e17);
+    vec4 _e19 = a;
+    vec4 _e25 = textureOffset(_group_0_binding_1_fs, vec2(_e1), ivec2(3, 1));
+    a = (_e19 + _e25);
+    vec4 _e27 = a;
+    vec4 _e30 = textureLod(_group_0_binding_1_fs, vec2(_e1), 2.3);
+    a = (_e27 + _e30);
+    vec4 _e32 = a;
+    vec4 _e35 = textureLodOffset(_group_0_binding_1_fs, vec2(_e1), 2.3, ivec2(3, 1));
+    a = (_e32 + _e35);
+    vec4 _e37 = a;
+    vec4 _e41 = textureOffset(_group_0_binding_1_fs, vec2(_e1), ivec2(3, 1), 2.0);
+    a = (_e37 + _e41);
+    vec4 _e43 = a;
+    vec4 _e46 = textureLod(_group_0_binding_1_fs, vec2(_e1), 0.0);
+    a = (_e43 + _e46);
+    vec4 _e48 = a;
+    vec4 _e52 = texture(_group_0_binding_4_fs, vec3(_e1, 0u));
+    a = (_e48 + _e52);
+    vec4 _e54 = a;
+    vec4 _e58 = textureOffset(_group_0_binding_4_fs, vec3(_e1, 0u), ivec2(3, 1));
+    a = (_e54 + _e58);
+    vec4 _e60 = a;
+    vec4 _e64 = textureLod(_group_0_binding_4_fs, vec3(_e1, 0u), 2.3);
+    a = (_e60 + _e64);
+    vec4 _e66 = a;
+    vec4 _e70 = textureLodOffset(_group_0_binding_4_fs, vec3(_e1, 0u), 2.3, ivec2(3, 1));
+    a = (_e66 + _e70);
+    vec4 _e72 = a;
+    vec4 _e77 = textureOffset(_group_0_binding_4_fs, vec3(_e1, 0u), ivec2(3, 1), 2.0);
+    a = (_e72 + _e77);
+    vec4 _e79 = a;
+    vec4 _e83 = texture(_group_0_binding_4_fs, vec3(_e1, 0));
+    a = (_e79 + _e83);
+    vec4 _e85 = a;
+    vec4 _e89 = textureOffset(_group_0_binding_4_fs, vec3(_e1, 0), ivec2(3, 1));
+    a = (_e85 + _e89);
+    vec4 _e91 = a;
+    vec4 _e95 = textureLod(_group_0_binding_4_fs, vec3(_e1, 0), 2.3);
+    a = (_e91 + _e95);
+    vec4 _e97 = a;
+    vec4 _e101 = textureLodOffset(_group_0_binding_4_fs, vec3(_e1, 0), 2.3, ivec2(3, 1));
+    a = (_e97 + _e101);
+    vec4 _e103 = a;
+    vec4 _e108 = textureOffset(_group_0_binding_4_fs, vec3(_e1, 0), ivec2(3, 1), 2.0);
+    a = (_e103 + _e108);
+    vec4 _e110 = a;
+    vec4 _e114 = texture(_group_0_binding_6_fs, vec4(_e3, 0u));
+    a = (_e110 + _e114);
+    vec4 _e116 = a;
+    vec4 _e120 = textureLod(_group_0_binding_6_fs, vec4(_e3, 0u), 2.3);
+    a = (_e116 + _e120);
+    vec4 _e122 = a;
+    vec4 _e127 = texture(_group_0_binding_6_fs, vec4(_e3, 0u), 2.0);
+    a = (_e122 + _e127);
+    vec4 _e129 = a;
+    vec4 _e133 = texture(_group_0_binding_6_fs, vec4(_e3, 0));
+    a = (_e129 + _e133);
+    vec4 _e135 = a;
+    vec4 _e139 = textureLod(_group_0_binding_6_fs, vec4(_e3, 0), 2.3);
+    a = (_e135 + _e139);
+    vec4 _e141 = a;
+    vec4 _e146 = texture(_group_0_binding_6_fs, vec4(_e3, 0), 2.0);
+    a = (_e141 + _e146);
     vec4 _e148 = a;
     _fs2p_location0 = _e148;
     return;

naga/tests/out/glsl/wgsl-image.texture_sample_comparison.Fragment.glsl

@@ -11,30 +11,30 @@ void main() {
     float a_1 = 0.0;
     vec2 tc = vec2(0.5);
     vec3 tc3_ = vec3(0.5);
-    float _e8 = texture(_group_1_binding_2_fs, vec3(tc, 0.5));
-    float _e9 = a_1;
-    a_1 = (_e9 + _e8);
-    float _e14 = texture(_group_1_binding_3_fs, vec4(tc, 0u, 0.5));
-    float _e15 = a_1;
-    a_1 = (_e15 + _e14);
-    float _e20 = texture(_group_1_binding_3_fs, vec4(tc, 0, 0.5));
-    float _e21 = a_1;
-    a_1 = (_e21 + _e20);
-    float _e25 = texture(_group_1_binding_4_fs, vec4(tc3_, 0.5));
-    float _e26 = a_1;
-    a_1 = (_e26 + _e25);
-    float _e30 = textureLod(_group_1_binding_2_fs, vec3(tc, 0.5), 0.0);
-    float _e31 = a_1;
-    a_1 = (_e31 + _e30);
-    float _e36 = textureGrad(_group_1_binding_3_fs, vec4(tc, 0u, 0.5), vec2(0.0), vec2(0.0));
-    float _e37 = a_1;
-    a_1 = (_e37 + _e36);
-    float _e42 = textureGrad(_group_1_binding_3_fs, vec4(tc, 0, 0.5), vec2(0.0), vec2(0.0));
-    float _e43 = a_1;
-    a_1 = (_e43 + _e42);
-    float _e47 = textureGrad(_group_1_binding_4_fs, vec4(tc3_, 0.5), vec3(0.0), vec3(0.0));
-    float _e48 = a_1;
-    a_1 = (_e48 + _e47);
+    float _e6 = a_1;
+    float _e9 = texture(_group_1_binding_2_fs, vec3(tc, 0.5));
+    a_1 = (_e6 + _e9);
+    float _e11 = a_1;
+    float _e15 = texture(_group_1_binding_3_fs, vec4(tc, 0u, 0.5));
+    a_1 = (_e11 + _e15);
+    float _e17 = a_1;
+    float _e21 = texture(_group_1_binding_3_fs, vec4(tc, 0, 0.5));
+    a_1 = (_e17 + _e21);
+    float _e23 = a_1;
+    float _e26 = texture(_group_1_binding_4_fs, vec4(tc3_, 0.5));
+    a_1 = (_e23 + _e26);
+    float _e28 = a_1;
+    float _e31 = textureLod(_group_1_binding_2_fs, vec3(tc, 0.5), 0.0);
+    a_1 = (_e28 + _e31);
+    float _e33 = a_1;
+    float _e37 = textureGrad(_group_1_binding_3_fs, vec4(tc, 0u, 0.5), vec2(0.0), vec2(0.0));
+    a_1 = (_e33 + _e37);
+    float _e39 = a_1;
+    float _e43 = textureGrad(_group_1_binding_3_fs, vec4(tc, 0, 0.5), vec2(0.0), vec2(0.0));
+    a_1 = (_e39 + _e43);
+    float _e45 = a_1;
+    float _e48 = textureGrad(_group_1_binding_4_fs, vec4(tc3_, 0.5), vec3(0.0), vec3(0.0));
+    a_1 = (_e45 + _e48);
     float _e50 = a_1;
     _fs2p_location0 = _e50;
     return;

naga/tests/out/glsl/wgsl-operators.main.Compute.glsl

@@ -37,12 +37,12 @@ vec4 splat(float m, int n) {
 
 vec2 splat_assignment() {
     vec2 a = vec2(2.0);
-    vec2 _e4 = a;
-    a = (_e4 + vec2(1.0));
-    vec2 _e8 = a;
-    a = (_e8 - vec2(3.0));
-    vec2 _e12 = a;
-    a = (_e12 / vec2(4.0));
+    vec2 _e3 = a;
+    a = (_e3 + vec2(1.0));
+    vec2 _e7 = a;
+    a = (_e7 - vec2(3.0));
+    vec2 _e11 = a;
+    a = (_e11 / vec2(4.0));
     vec2 _e15 = a;
     return _e15;
 }
@@ -291,10 +291,10 @@ void assignment() {
     a_1 = (_e7 - 1);
     int _e9 = a_1;
     int _e10 = a_1;
-    a_1 = (_e10 * _e9);
+    a_1 = (_e9 * _e10);
     int _e12 = a_1;
     int _e13 = a_1;
-    a_1 = (_e13 / _e12);
+    a_1 = (_e12 / _e13);
     int _e15 = a_1;
     a_1 = (_e15 % 1);
     int _e17 = a_1;

naga/tests/out/glsl/wgsl-shadow.fs_main.Fragment.glsl

@@ -72,8 +72,8 @@ void main() {
             float _e23 = fetch_shadow(_e19, (light.proj * in_.world_position));
             vec3 light_dir = normalize((light.pos.xyz - in_.world_position.xyz));
             float diffuse = max(0.0, dot(normal_1, light_dir));
-            vec3 _e37 = color;
-            color = (_e37 + ((_e23 * diffuse) * light.color.xyz));
+            vec3 _e33 = color;
+            color = (_e33 + ((_e23 * diffuse) * light.color.xyz));
         }
     }
     vec3 _e42 = color;

naga/tests/out/glsl/wgsl-shadow.fs_main_without_storage.Fragment.glsl

@@ -72,8 +72,8 @@ void main() {
             float _e23 = fetch_shadow(_e19, (light.proj * in_1.world_position));
             vec3 light_dir = normalize((light.pos.xyz - in_1.world_position.xyz));
             float diffuse = max(0.0, dot(normal_1, light_dir));
-            vec3 _e37 = color_1;
-            color_1 = (_e37 + ((_e23 * diffuse) * light.color.xyz));
+            vec3 _e33 = color_1;
+            color_1 = (_e33 + ((_e23 * diffuse) * light.color.xyz));
         }
     }
     vec3 _e42 = color_1;