spirv-reader: switch to HLSL-style pipeline IO

- When storing to sample_mask output, write to the 0th element
- Only make a return struct if it has members
- Adjust type signedness coercion when loading special builtins.
- Adapt tests

- Update expectations for end-to-end tests

- Handle sample_mask with stride
  Input variables normally don't have layout. But they can have it
  up through SPIR-V 1.4.
  Handle this case in the SPIR-V reader, by seeing through the
  intermediate alias type created for the strided array type.

Bug: tint:508
Change-Id: I0f19dc1305d3f250dbbc0698a602288c34245274
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/54743
Auto-Submit: David Neto <dneto@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: James Price <jrprice@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>

test/samples/simple_vertex.spvasm.expected.msl

@@ -1,13 +1,23 @@
 #include <metal_stdlib>
 
 using namespace metal;
-struct tint_symbol_out {
+struct main_out {
+  float4 gl_Position;
+};
+struct tint_symbol_1 {
   float4 gl_Position [[position]];
 };
 
-vertex tint_symbol_out tint_symbol() {
-  tint_symbol_out _tint_out = {};
-  _tint_out.gl_Position = float4(0.0f, 0.0f, 0.0f, 0.0f);
-  return _tint_out;
+void main_1(thread float4* const tint_symbol_4) {
+  *(tint_symbol_4) = float4(0.0f, 0.0f, 0.0f, 0.0f);
+  return;
+}
+
+vertex tint_symbol_1 tint_symbol() {
+  thread float4 tint_symbol_5 = 0.0f;
+  main_1(&(tint_symbol_5));
+  main_out const tint_symbol_2 = {.gl_Position=tint_symbol_5};
+  tint_symbol_1 const tint_symbol_3 = {.gl_Position=tint_symbol_2.gl_Position};
+  return tint_symbol_3;
 }
 

test/samples/simple_vertex.spvasm.expected.spvasm

@@ -1,32 +1,58 @@
 ; SPIR-V
 ; Version: 1.3
 ; Generator: Google Tint Compiler; 0
-; Bound: 16
+; Bound: 30
 ; Schema: 0
                OpCapability Shader
                OpMemoryModel Logical GLSL450
-               OpEntryPoint Vertex %main "main" %tint_pointsize %gl_Position
+               OpEntryPoint Vertex %main "main" %tint_pointsize %tint_symbol_1
                OpName %tint_pointsize "tint_pointsize"
                OpName %gl_Position "gl_Position"
+               OpName %tint_symbol_1 "tint_symbol_1"
+               OpName %main_1 "main_1"
+               OpName %main_out "main_out"
+               OpMemberName %main_out 0 "gl_Position"
+               OpName %tint_symbol_2 "tint_symbol_2"
+               OpName %tint_symbol "tint_symbol"
                OpName %main "main"
                OpDecorate %tint_pointsize BuiltIn PointSize
-               OpDecorate %gl_Position BuiltIn Position
+               OpDecorate %tint_symbol_1 BuiltIn Position
+               OpMemberDecorate %main_out 0 Offset 0
       %float = OpTypeFloat 32
 %_ptr_Output_float = OpTypePointer Output %float
           %4 = OpConstantNull %float
 %tint_pointsize = OpVariable %_ptr_Output_float Output %4
     %v4float = OpTypeVector %float 4
-%_ptr_Output_v4float = OpTypePointer Output %v4float
+%_ptr_Private_v4float = OpTypePointer Private %v4float
           %8 = OpConstantNull %v4float
-%gl_Position = OpVariable %_ptr_Output_v4float Output %8
+%gl_Position = OpVariable %_ptr_Private_v4float Private %8
+%_ptr_Output_v4float = OpTypePointer Output %v4float
+%tint_symbol_1 = OpVariable %_ptr_Output_v4float Output %8
        %void = OpTypeVoid
-          %9 = OpTypeFunction %void
-    %float_1 = OpConstant %float 1
+         %11 = OpTypeFunction %void
     %float_0 = OpConstant %float 0
-         %15 = OpConstantComposite %v4float %float_0 %float_0 %float_0 %float_0
-       %main = OpFunction %void None %9
-         %12 = OpLabel
-               OpStore %tint_pointsize %float_1
-               OpStore %gl_Position %15
+         %16 = OpConstantComposite %v4float %float_0 %float_0 %float_0 %float_0
+   %main_out = OpTypeStruct %v4float
+         %17 = OpTypeFunction %void %main_out
+    %float_1 = OpConstant %float 1
+     %main_1 = OpFunction %void None %11
+         %14 = OpLabel
+               OpStore %gl_Position %16
+               OpReturn
+               OpFunctionEnd
+%tint_symbol_2 = OpFunction %void None %17
+%tint_symbol = OpFunctionParameter %main_out
+         %21 = OpLabel
+         %22 = OpCompositeExtract %v4float %tint_symbol 0
+               OpStore %tint_symbol_1 %22
+               OpReturn
+               OpFunctionEnd
+       %main = OpFunction %void None %11
+         %24 = OpLabel
+               OpStore %tint_pointsize %float_1
+         %26 = OpFunctionCall %void %main_1
+         %28 = OpLoad %v4float %gl_Position
+         %29 = OpCompositeConstruct %main_out %28
+         %27 = OpFunctionCall %void %tint_symbol_2 %29
                OpReturn
                OpFunctionEnd

test/samples/simple_vertex.spvasm.expected.wgsl

@@ -1,7 +1,17 @@
-[[builtin(position)]] var<out> gl_Position : vec4<f32>;
+var<private> gl_Position : vec4<f32>;
 
-[[stage(vertex)]]
-fn main() {
+fn main_1() {
   gl_Position = vec4<f32>(0.0, 0.0, 0.0, 0.0);
   return;
 }
+
+struct main_out {
+  [[builtin(position)]]
+  gl_Position : vec4<f32>;
+};
+
+[[stage(vertex)]]
+fn main() -> main_out {
+  main_1();
+  return main_out(gl_Position);
+}