Fixed SkSL positioning error with double negation

We were not propagating the position into a double-negated expression,
leading to an assertion failure in PrefixExpression.

Change-Id: I1970ff1a06d9631582626c68e151f12f6b3ef278
Bug: oss-fuzz:46381
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/527507
Reviewed-by: Brian Osman <brianosman@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>

gn/sksl_tests.gni

@@ -410,6 +410,7 @@ sksl_shared_tests = [
   "/sksl/shared/DependentInitializers.sksl",
   "/sksl/shared/DerivativesUnused.sksl",
   "/sksl/shared/Discard.sksl",
+  "/sksl/shared/DoubleNegation.sksl",
   "/sksl/shared/DoWhileControlFlow.sksl",
   "/sksl/shared/EmptyBlocksES2.sksl",
   "/sksl/shared/EmptyBlocksES3.sksl",

resources/sksl/shared/DoubleNegation.sksl

@@ -0,0 +1,5 @@
+uniform half4 colorGreen;
+
+half4 main(float2 coords) {
+    return half4(half(-(-int(colorGreen.r))), -(-colorGreen.g), -(-(colorGreen.ba)));
+}

src/sksl/ir/SkSLExpression.h

@@ -206,6 +206,15 @@ public:
 
     virtual std::unique_ptr<Expression> clone() const = 0;
 
+    /**
+     * Returns a clone with a modified position.
+     */
+    std::unique_ptr<Expression> clone(Position pos) {
+        std::unique_ptr<Expression> result = this->clone();
+        result->fPosition = pos;
+        return result;
+    }
+
 private:
     const Type* fType;
 

src/sksl/ir/SkSLPrefixExpression.cpp

@@ -44,7 +44,7 @@ static std::unique_ptr<Expression> simplify_negation(const Context& context,
             // Convert `-(-expression)` into `expression`.
             const PrefixExpression& prefix = value->as<PrefixExpression>();
             if (prefix.getOperator().kind() == Operator::Kind::MINUS) {
-                return prefix.operand()->clone();
+                return prefix.operand()->clone(pos);
             }
             break;
         }

tests/SkSLTest.cpp

@@ -455,6 +455,7 @@ SKSL_TEST(CPU + GPU + SkQP, DeadReturn,                      "shared/DeadReturn.
 // SKSL_TEST(GPU_ES3,       SkSLDeadReturnES3,               "shared/DeadReturnES3.sksl")
 SKSL_TEST(CPU + GPU + SkQP, DeadStripFunctions,              "shared/DeadStripFunctions.sksl")
 SKSL_TEST(CPU + GPU + SkQP, DependentInitializers,           "shared/DependentInitializers.sksl")
+SKSL_TEST(CPU + GPU + SkQP, DoubleNegation,                  "shared/DoubleNegation.sksl")
 SKSL_TEST(GPU_ES3,          DoWhileControlFlow,              "shared/DoWhileControlFlow.sksl")
 SKSL_TEST(CPU + GPU + SkQP, EmptyBlocksES2,                  "shared/EmptyBlocksES2.sksl")
 SKSL_TEST(GPU_ES3,          EmptyBlocksES3,                  "shared/EmptyBlocksES3.sksl")

tests/sksl/shared/DoubleNegation.asm.frag

@@ -0,0 +1,77 @@
+OpCapability Shader
+%1 = OpExtInstImport "GLSL.std.450"
+OpMemoryModel Logical GLSL450
+OpEntryPoint Fragment %_entrypoint_v "_entrypoint" %sk_FragColor %sk_Clockwise
+OpExecutionMode %_entrypoint_v OriginUpperLeft
+OpName %sk_FragColor "sk_FragColor"
+OpName %sk_Clockwise "sk_Clockwise"
+OpName %_UniformBuffer "_UniformBuffer"
+OpMemberName %_UniformBuffer 0 "colorGreen"
+OpName %_entrypoint_v "_entrypoint_v"
+OpName %main "main"
+OpDecorate %sk_FragColor RelaxedPrecision
+OpDecorate %sk_FragColor Location 0
+OpDecorate %sk_FragColor Index 0
+OpDecorate %sk_Clockwise BuiltIn FrontFacing
+OpMemberDecorate %_UniformBuffer 0 Offset 0
+OpMemberDecorate %_UniformBuffer 0 RelaxedPrecision
+OpDecorate %_UniformBuffer Block
+OpDecorate %10 Binding 0
+OpDecorate %10 DescriptorSet 0
+OpDecorate %30 RelaxedPrecision
+OpDecorate %31 RelaxedPrecision
+OpDecorate %33 RelaxedPrecision
+OpDecorate %35 RelaxedPrecision
+OpDecorate %36 RelaxedPrecision
+OpDecorate %38 RelaxedPrecision
+OpDecorate %39 RelaxedPrecision
+OpDecorate %40 RelaxedPrecision
+OpDecorate %41 RelaxedPrecision
+OpDecorate %42 RelaxedPrecision
+%float = OpTypeFloat 32
+%v4float = OpTypeVector %float 4
+%_ptr_Output_v4float = OpTypePointer Output %v4float
+%sk_FragColor = OpVariable %_ptr_Output_v4float Output
+%bool = OpTypeBool
+%_ptr_Input_bool = OpTypePointer Input %bool
+%sk_Clockwise = OpVariable %_ptr_Input_bool Input
+%_UniformBuffer = OpTypeStruct %v4float
+%_ptr_Uniform__UniformBuffer = OpTypePointer Uniform %_UniformBuffer
+%10 = OpVariable %_ptr_Uniform__UniformBuffer Uniform
+%void = OpTypeVoid
+%15 = OpTypeFunction %void
+%v2float = OpTypeVector %float 2
+%float_0 = OpConstant %float 0
+%19 = OpConstantComposite %v2float %float_0 %float_0
+%_ptr_Function_v2float = OpTypePointer Function %v2float
+%23 = OpTypeFunction %v4float %_ptr_Function_v2float
+%_ptr_Uniform_v4float = OpTypePointer Uniform %v4float
+%int = OpTypeInt 32 1
+%int_0 = OpConstant %int 0
+%_entrypoint_v = OpFunction %void None %15
+%16 = OpLabel
+%20 = OpVariable %_ptr_Function_v2float Function
+OpStore %20 %19
+%22 = OpFunctionCall %v4float %main %20
+OpStore %sk_FragColor %22
+OpReturn
+OpFunctionEnd
+%main = OpFunction %v4float None %23
+%24 = OpFunctionParameter %_ptr_Function_v2float
+%25 = OpLabel
+%26 = OpAccessChain %_ptr_Uniform_v4float %10 %int_0
+%30 = OpLoad %v4float %26
+%31 = OpCompositeExtract %float %30 0
+%32 = OpConvertFToS %int %31
+%33 = OpConvertSToF %float %32
+%34 = OpAccessChain %_ptr_Uniform_v4float %10 %int_0
+%35 = OpLoad %v4float %34
+%36 = OpCompositeExtract %float %35 1
+%37 = OpAccessChain %_ptr_Uniform_v4float %10 %int_0
+%38 = OpLoad %v4float %37
+%39 = OpVectorShuffle %v2float %38 %38 2 3
+%40 = OpCompositeExtract %float %39 0
+%41 = OpCompositeExtract %float %39 1
+%42 = OpCompositeConstruct %v4float %33 %36 %40 %41
+OpReturnValue %42
+OpFunctionEnd

tests/sksl/shared/DoubleNegation.glsl

@@ -0,0 +1,6 @@
+
+out vec4 sk_FragColor;
+uniform vec4 colorGreen;
+vec4 main() {
+    return vec4(float(int(colorGreen.x)), colorGreen.y, colorGreen.zw);
+}

tests/sksl/shared/DoubleNegation.metal

@@ -0,0 +1,17 @@
+#include <metal_stdlib>
+#include <simd/simd.h>
+using namespace metal;
+struct Uniforms {
+    half4 colorGreen;
+};
+struct Inputs {
+};
+struct Outputs {
+    half4 sk_FragColor [[color(0)]];
+};
+fragment Outputs fragmentMain(Inputs _in [[stage_in]], constant Uniforms& _uniforms [[buffer(0)]], bool _frontFacing [[front_facing]], float4 _fragCoord [[position]]) {
+    Outputs _out;
+    (void)_out;
+    _out.sk_FragColor = half4(half(int(_uniforms.colorGreen.x)), _uniforms.colorGreen.y, _uniforms.colorGreen.zw);
+    return _out;
+}