Add test for split of `--`.

An expression like `b--b` needs the `--` split into two symbols in
order to parse correctly. This change was done previously, adding
a test case to show the generated output.

Bug: tint:988
Change-Id: Id389224e33b7702a90e4c157b02031fb605c1b14
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/106580
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Auto-Submit: Dan Sinclair <dsinclair@chromium.org>
Commit-Queue: Antonio Maiorano <amaiorano@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>

test/tint/statements/decrement/split.wgsl

@@ -0,0 +1,4 @@
+fn main() {
+  var b = 2;
+  var c = b--b;
+}

test/tint/statements/decrement/split.wgsl.expected.dxc.hlsl

@@ -0,0 +1,9 @@
+[numthreads(1, 1, 1)]
+void unused_entry_point() {
+  return;
+}
+
+void main() {
+  int b = 2;
+  int c = (b - -(b));
+}

test/tint/statements/decrement/split.wgsl.expected.fxc.hlsl

@@ -0,0 +1,9 @@
+[numthreads(1, 1, 1)]
+void unused_entry_point() {
+  return;
+}
+
+void main() {
+  int b = 2;
+  int c = (b - -(b));
+}

test/tint/statements/decrement/split.wgsl.expected.glsl

@@ -0,0 +1,11 @@
+#version 310 es
+
+layout(local_size_x = 1, local_size_y = 1, local_size_z = 1) in;
+void unused_entry_point() {
+  return;
+}
+void tint_symbol() {
+  int b = 2;
+  int c = (b - -(b));
+}
+

test/tint/statements/decrement/split.wgsl.expected.msl

@@ -0,0 +1,13 @@
+#include <metal_stdlib>
+
+using namespace metal;
+
+int tint_unary_minus(const int v) {
+  return select(-v, v, v == -2147483648);
+}
+
+void tint_symbol() {
+  int b = 2;
+  int c = as_type<int>((as_type<uint>(b) - as_type<uint>(tint_unary_minus(b))));
+}
+

test/tint/statements/decrement/split.wgsl.expected.spvasm

@@ -0,0 +1,35 @@
+; SPIR-V
+; Version: 1.3
+; Generator: Google Tint Compiler; 0
+; Bound: 17
+; Schema: 0
+               OpCapability Shader
+               OpMemoryModel Logical GLSL450
+               OpEntryPoint GLCompute %unused_entry_point "unused_entry_point"
+               OpExecutionMode %unused_entry_point LocalSize 1 1 1
+               OpName %unused_entry_point "unused_entry_point"
+               OpName %main "main"
+               OpName %b "b"
+               OpName %c "c"
+       %void = OpTypeVoid
+          %1 = OpTypeFunction %void
+        %int = OpTypeInt 32 1
+      %int_2 = OpConstant %int 2
+%_ptr_Function_int = OpTypePointer Function %int
+         %11 = OpConstantNull %int
+%unused_entry_point = OpFunction %void None %1
+          %4 = OpLabel
+               OpReturn
+               OpFunctionEnd
+       %main = OpFunction %void None %1
+          %6 = OpLabel
+          %b = OpVariable %_ptr_Function_int Function %11
+          %c = OpVariable %_ptr_Function_int Function %11
+               OpStore %b %int_2
+         %12 = OpLoad %int %b
+         %14 = OpLoad %int %b
+         %13 = OpSNegate %int %14
+         %15 = OpISub %int %12 %13
+               OpStore %c %15
+               OpReturn
+               OpFunctionEnd

test/tint/statements/decrement/split.wgsl.expected.wgsl

@@ -0,0 +1,4 @@
+fn main() {
+  var b = 2;
+  var c = (b - -(b));
+}