Pick correct GLSL version when `gl_Layer` used

`gl_Layer` as a fragment input requires at least version 4.30 of GLSL, so we try to track that information when we see the name used.

Note that this does *not* override a user-specified `#version` line.

This required re-ordering when lowering happens relative to emitting the `#version` directive, since this code works by actually modifying the chosen profile for the entry point.
Yes, that is kind of gross and we should do something cleaner in the long term.

5 files changed, 80 insertions, 4 deletions

diff --git a/source/slang/emit.cpp b/source/slang/emit.cpp
index 8c6a46196..0eb371b88 100644
--- a/source/slang/emit.cpp
+++ b/source/slang/emit.cpp
@@ -3604,6 +3604,13 @@ String emitEntryPoint(
 
     auto translationUnitSyntax = translationUnit->SyntaxNode.Ptr();
 
+    // We perform lowering of the program before emitting *anything*,
+    // because the lowering process might change how we emit some
+    // boilerplate at the start of the ouput for GLSL (e.g., what
+    // version we require).
+    auto lowered = lowerEntryPoint(entryPoint, programLayout, target);
+    sharedContext.program = lowered.program;
+
 
     // There may be global-scope modifiers that we should emit now
     visitor.emitGLSLPreprocessorDirectives(translationUnitSyntax);
@@ -3624,9 +3631,6 @@ String emitEntryPoint(
         break;
     }
 
-    auto lowered = lowerEntryPoint(entryPoint, programLayout, target);
-
-    sharedContext.program = lowered.program;
 
     visitor.EmitDeclsInContainer(lowered.program.Ptr());
 
diff --git a/source/slang/lower.cpp b/source/slang/lower.cpp
index 856da9b6c..98f6d8273 100644
--- a/source/slang/lower.cpp
+++ b/source/slang/lower.cpp
@@ -221,7 +221,8 @@ public:
 
 struct SharedLoweringContext
 {
-    CompileRequest* compileRequest;
+    CompileRequest*     compileRequest;
+    EntryPointRequest*  entryPointRequest;
 
     ProgramLayout*      programLayout;
     EntryPointLayout*   entryPointLayout;
@@ -2329,6 +2330,31 @@ struct LoweringVisitor
         return false;
     }
 
+    void requireGLSLVersion(ProfileVersion version)
+    {
+        if (shared->target != CodeGenTarget::GLSL)
+            return;
+
+        auto entryPoint = shared->entryPointRequest;
+        auto profile = entryPoint->profile;
+        auto currentVersion = profile.GetVersion();
+        if (profile.getFamily() == ProfileFamily::GLSL)
+        {
+            // Check if this profile is newer
+            if ((UInt)version > (UInt)profile.GetVersion())
+            {
+                profile.setVersion(version);
+                entryPoint->profile = profile;
+            }
+        }
+        else
+        {
+            // Non-GLSL target? Set it to a GLSL one.
+            profile.setVersion(version);
+            entryPoint->profile = profile;
+        }
+    }
+
     void lowerSimpleShaderParameterToGLSLGlobal(
         VaryingParameterInfo const&     info,
         RefPtr<ExpressionType>          varType,
@@ -2460,6 +2486,10 @@ struct LoweringVisitor
             }
             else if (ns == "sv_rendertargetarrayindex")
             {
+                if (info.direction == VaryingParameterDirection::Input)
+                {
+                    requireGLSLVersion(ProfileVersion::GLSL_430);
+                }
                 globalVarExpr = createGLSLBuiltinRef("gl_Layer");
             }
             else if (ns == "sv_sampleindex")
@@ -3040,6 +3070,7 @@ LoweredEntryPoint lowerEntryPoint(
 {
     SharedLoweringContext sharedContext;
     sharedContext.compileRequest = entryPoint->compileRequest;
+    sharedContext.entryPointRequest = entryPoint;
     sharedContext.programLayout = programLayout;
     sharedContext.target = target;
 
diff --git a/source/slang/profile.h b/source/slang/profile.h
index 6d55d3195..3b5242ada 100644
--- a/source/slang/profile.h
+++ b/source/slang/profile.h
@@ -70,6 +70,11 @@ namespace Slang
         ProfileVersion GetVersion() const { return ProfileVersion(uint32_t(raw) & 0xFFFF); }
         ProfileFamily getFamily() const { return getProfileFamily(GetVersion()); }
 
+        void setVersion(ProfileVersion version)
+        {
+            raw = (raw & ~0xFFFF) | uint32_t(version);
+        }
+
         static Profile LookUp(char const* name);
 
         RawVal raw = Unknown;
diff --git a/tests/cross-compile/gl-layer-pick-version.slang b/tests/cross-compile/gl-layer-pick-version.slang
new file mode 100644
index 000000000..c68d68427
--- /dev/null
+++ b/tests/cross-compile/gl-layer-pick-version.slang
@@ -0,0 +1,11 @@
+//TEST:CROSS_COMPILE: -profile ps_5_0 -entry main -target spirv-assembly
+
+struct VS_OUT
+{
+	nointerpolation uint layerID : SV_RenderTargetArrayIndex;	
+};
+
+float4 main(VS_OUT vsOut) : SV_Target
+{
+	return float4(float(vsOut.layerID));
+}
diff --git a/tests/cross-compile/gl-layer-pick-version.slang.glsl b/tests/cross-compile/gl-layer-pick-version.slang.glsl
new file mode 100644
index 000000000..55d419405
--- /dev/null
+++ b/tests/cross-compile/gl-layer-pick-version.slang.glsl
@@ -0,0 +1,25 @@
+//TEST_IGNORE_FILE:
+#version 430
+
+struct VS_OUT
+{
+	uint layerID;
+};
+
+vec4 main_(VS_OUT vsOut) : SV_Target
+{
+	return vec4(float(vsOut.layerID));
+}
+
+out vec4 SLANG_out_main_result;
+
+void main()
+{
+	VS_OUT vsOut;
+	vsOut.layerID = gl_Layer;
+
+	vec4 main_result;
+	main_result = main_(vsOut);
+
+	SLANG_out_main_result = main_result;
+}
\ No newline at end of file