Fix crash when using GLSL global uniforms and varying inputs/ouputs together (#6651)

* Fix incorrect assert on mixed global uniform and varyings

* add test

* remove unnecessary include

* fix incorrect logic

* fix comment grammar

* address review comments and improve test

* minimize diff

* fix more issues for cuda build

* remove unnecessary line for diff

2 files changed, 37 insertions, 6 deletions

diff --git a/source/slang/slang-ir-collect-global-uniforms.cpp b/source/slang/slang-ir-collect-global-uniforms.cpp
index 372ef298e..fb2a2233c 100644
--- a/source/slang/slang-ir-collect-global-uniforms.cpp
+++ b/source/slang/slang-ir-collect-global-uniforms.cpp
@@ -179,16 +179,15 @@ struct CollectGlobalUniformParametersContext
             // We expect the IR layout pass to have encoded field per-field
             // layout so that the "key" for the field is the corresponding
             // global shader parameter.
-            //
+
+            // Save the original global param before replacement.
             auto globalParam = _getGlobalParamFromLayoutFieldKey(fieldLayoutAttr->getFieldKey());
-            SLANG_ASSERT(globalParam);
 
             auto globalParamLayout = fieldLayoutAttr->getLayout();
 
-            // Once we have decided to do replacement, we need to
-            // set ourselves up to emit the replacement code.
-            //
-            builder->setInsertBefore(globalParam);
+            // Set insert position to a valid instruction under the global parent scope so we can
+            // create struct keys.
+            builder->setInsertAfter(fieldLayoutAttr->getFieldKey());
 
             // This global parameter needs to be turned into a field of the global
             // parameter structure type, and that field will need a key.
@@ -216,6 +215,8 @@ struct CollectGlobalUniformParametersContext
             if (!globalParamLayout->getTypeLayout()->findSizeAttr(LayoutResourceKind::Uniform))
                 continue;
 
+            SLANG_ASSERT(globalParam);
+
             // The new structure field will need to have whatever decorations
             // had been put on the global parameter (notably including any name hint)
             //
diff --git a/tests/glsl/global-uniform-with-varyings.slang b/tests/glsl/global-uniform-with-varyings.slang
new file mode 100644
index 000000000..678855dbf
--- /dev/null
+++ b/tests/glsl/global-uniform-with-varyings.slang
@@ -0,0 +1,30 @@
+//TEST:SIMPLE(filecheck=CHECK_SPIRV): -target spirv -entry main -stage vertex
+//TEST:SIMPLE(filecheck=CHECK_GLSL): -target glsl -entry main -stage vertex
+
+// CHECK_SPIRV: OpEntryPoint
+// CHECK_SPIRV: OpVariable {{.*}} Input {{.*}} Location 0
+// CHECK_SPIRV: OpVariable {{.*}} Uniform
+// CHECK_SPIRV: OpVariable {{.*}} Input {{.*}} Location 1
+// CHECK_SPIRV: OpVariable {{.*}} Output {{.*}} Location 0
+
+// CHECK_GLSL: layout(location = 0)
+// CHECK_GLSL-NEXT: in
+// CHECK_GLSL: layout(location = 1)
+// CHECK_GLSL-NEXT: in
+// CHECK_GLSL: layout(std140) uniform
+// CHECK_GLSL: layout(location = 0)
+// CHECK_GLSL-NEXT: out
+// CHECK_GLSL: void main
+
+#version 330 core
+layout(location=0) in float3 a_position;
+layout(location=1) in float4 a_color;
+
+out float4 v_color;
+
+uniform matrix<float,4,4> u_transform;
+
+void main() {
+    gl_Position = u_transform * vec4(a_position, 1.0);
+    v_color = a_color;
+}