Fix varying output structs in GLSL source (#8501)

Closes #8500.

`slang-ir-translate-global-varying-var.cpp` turns the global varying
outputs into a struct that's returned from the entry point. Currently,
there's a problem when one of the outputs is a struct. It always creates
a generic `IRTypeLayout`, even when a correct type layout already
exists. Somehow, this appears to work when the global varying outputs
aren't structs.

The crash occurs in
`slang-ir-glsl-legalize.cpp:createGLSLGlobalVaryingsImpl()`. It
correctly handles the generated outer struct, but when that contains an
inner struct, it's been given a non-struct type layout and crashes.

This PR uses the correct layout if found, instead of generating a broken
placeholder. This matches the behaviour that has already been
implemented for inputs.

Additionally, I removed a call to `addResourceUsage` from both the input
and output side. I can't see any way in which it would've affected
anything, the layout builder is never used after that call and it
doesn't retroactively modify the layout that was already created.

1 files changed, 11 insertions, 3 deletions

diff --git a/tests/glsl/interface-block.glsl b/tests/glsl/interface-block.glsl
index 3d18db6c7..8378de7bf 100644
--- a/tests/glsl/interface-block.glsl
+++ b/tests/glsl/interface-block.glsl
@@ -1,7 +1,10 @@
 //TEST:SIMPLE(filecheck=CHECK_GLSL): -target glsl -stage fragment -entry fragmentMain -allow-glsl
 
 //CHECK_GLSL: layout(location = 0)
-//CHECK_GLSL: out vec4 entryPointParam_fragmentMain_out1_0;
+//CHECK_GLSL: out vec4 entryPointParam_fragmentMain_cd_out1_0;
+
+//CHECK_GLSL: layout(location = 1)
+//CHECK_GLSL: out vec4 entryPointParam_fragmentMain_cd_out2_0;
 
 //CHECK_GLSL: layout(location = 0)
 //CHECK_GLSL: in vec2 vd_texcoord_0_0;
@@ -28,10 +31,15 @@ in VertexData
     innerData inner;
 } vd;
 
-out vec4 out1;
+out ColorData
+{
+    vec4 out1;
+    vec4 out2;
+} cd;
 
 void fragmentMain()
 {
-    out1 = vec4(vd.texcoord_0, vd.texcoord_1.x, vd.inner.texcoord_2.y);
+    cd.out1 = vec4(vd.texcoord_0, vd.texcoord_1.x, vd.inner.texcoord_2.y);
+    cd.out2 = vec4(vd.texcoord_1, vd.texcoord_0.x, vd.inner.texcoord_2.y);
 }