From 1300678a36bf8d7081647aef3e2a37dbd496aaf5 Mon Sep 17 00:00:00 2001
From: Ronan <ro.cailleau@gmail.com>
Date: Wed, 8 Oct 2025 11:19:13 +0200
Subject: `ExprLoweringVisitorBase::getDefaultVal(Type*)` use
 `MakeVector/MatrixFromScalar` (#8512)

- Allows using `Vector/Matrix` type with yet unresolved dimensions
- Simpler implementation and in-line with default `Array`
- Added `test/bugs/gh-8512.slang`
---
 source/slang/slang-lower-to-ir.cpp | 25 ++++--------------------
 tests/bugs/gh-8512-2.slang         | 40 ++++++++++++++++++++++++++++++++++++++
 tests/bugs/gh-8512.slang           | 39 +++++++++++++++++++++++++++++++++++++
 3 files changed, 83 insertions(+), 21 deletions(-)
 create mode 100644 tests/bugs/gh-8512-2.slang
 create mode 100644 tests/bugs/gh-8512.slang

diff --git a/source/slang/slang-lower-to-ir.cpp b/source/slang/slang-lower-to-ir.cpp
index d3f7d4e4c..c4492cfbb 100644
--- a/source/slang/slang-lower-to-ir.cpp
+++ b/source/slang/slang-lower-to-ir.cpp
@@ -4948,34 +4948,17 @@ struct ExprLoweringVisitorBase : public ExprVisitor<Derived, LoweredValInfo>
         }
         else if (auto vectorType = as<VectorExpressionType>(type))
         {
-            UInt elementCount = (UInt)getIntVal(vectorType->getElementCount());
-
             auto irDefaultValue =
                 getSimpleVal(context, getDefaultVal(vectorType->getElementType()));
-
-            List<IRInst*> args;
-            for (UInt ee = 0; ee < elementCount; ++ee)
-            {
-                args.add(irDefaultValue);
-            }
             return LoweredValInfo::simple(
-                getBuilder()->emitMakeVector(irType, args.getCount(), args.getBuffer()));
+                getBuilder()->emitMakeVectorFromScalar(irType, irDefaultValue));
         }
         else if (auto matrixType = as<MatrixExpressionType>(type))
         {
-            UInt rowCount = (UInt)getIntVal(matrixType->getRowCount());
-
-            auto rowType = matrixType->getRowType();
-
-            auto irDefaultValue = getSimpleVal(context, getDefaultVal(rowType));
-
-            List<IRInst*> args;
-            for (UInt rr = 0; rr < rowCount; ++rr)
-            {
-                args.add(irDefaultValue);
-            }
+            auto irDefaultValue =
+                getSimpleVal(context, getDefaultVal(matrixType->getElementType()));
             return LoweredValInfo::simple(
-                getBuilder()->emitMakeMatrix(irType, args.getCount(), args.getBuffer()));
+                getBuilder()->emitMakeMatrixFromScalar(irType, irDefaultValue));
         }
         else if (auto arrayType = as<ArrayExpressionType>(type))
         {
diff --git a/tests/bugs/gh-8512-2.slang b/tests/bugs/gh-8512-2.slang
new file mode 100644
index 000000000..4c51af696
--- /dev/null
+++ b/tests/bugs/gh-8512-2.slang
@@ -0,0 +1,40 @@
+//TEST:INTERPRET(filecheck=ICHECK):
+
+__generic <Scalar : __BuiltinFloatingPointType, int Mode>
+struct Spectrum
+{
+	static const int Samples = Mode & 0xFF;
+	typealias VecT = vector<Scalar, Samples>;
+	VecT data;
+	
+	static const bool IsRGB = (Mode & 0x100) != 0;
+
+	__generic <Float : __BuiltinFloatingPointType>
+	__init(vector<Float, Samples> v)
+	{
+		this.data = VecT(v);
+	}
+
+	static This MakeFromRGB<Float : __BuiltinFloatingPointType>(vector<Float, 3> rgb)
+	{
+		if(IsRGB)
+		{
+			return (Spectrum<Scalar, 0x103>(rgb) as This).value;
+		}
+		else
+		{
+			return {};
+		}
+	}
+}
+
+static const int DefaultMode = 0x103;
+typealias Spec = Spectrum<float, DefaultMode>;
+
+void main()
+{
+	float3 color = {1, 2, 3};
+	let spec = Spec::MakeFromRGB(color);
+	// ICHECK: (1, 2, 3)
+	printf("(%.0f, %.0f, %.0f)", spec.data[0], spec.data[1], spec.data[2]);
+}
diff --git a/tests/bugs/gh-8512.slang b/tests/bugs/gh-8512.slang
new file mode 100644
index 000000000..e94d95719
--- /dev/null
+++ b/tests/bugs/gh-8512.slang
@@ -0,0 +1,39 @@
+//TEST:SIMPLE(filecheck=CHECK): -target spirv
+// CHECK: OpEntryPoint
+
+__generic <Scalar : __BuiltinFloatingPointType, int Mode>
+struct Spectrum
+{
+	static const int Samples = Mode & 0xFF;
+	typealias VecT = vector<Scalar, Samples>;
+	VecT data;
+	
+	static const bool IsRGB = (Mode & 0x100) != 0;
+
+	__generic <Float : __BuiltinFloatingPointType>
+	__init(vector<Float, Samples> v)
+	{
+		this.data = VecT(v);
+	}
+
+	static This MakeFromRGB<Float : __BuiltinFloatingPointType>(vector<Float, 3> rgb)
+	{
+		if(IsRGB)
+		{
+			return (Spectrum<Scalar, 0x103>(rgb) as This).value;
+		}
+		else
+		{
+			return {};
+		}
+	}
+}
+
+static const int DefaultMode = 0x103;
+typealias Spec = Spectrum<float, DefaultMode>;
+
+[shader("vertex")]
+Spec main(float3 vertex_color : COLOR0) : COLOR0
+{
+	return Spec::MakeFromRGB(vertex_color);
+}
-- 
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