Do not unpack transposed matrices.

reference/opt/shaders-msl/comp/struct-packing.comp

@@ -121,6 +121,6 @@ kernel void main0(device SSBO0& ssbo_140 [[buffer(0)]], device SSBO1& ssbo_430 [
     ssbo_430.content.m3s[5].c = _60.m3s[5].c;
     ssbo_430.content.m3s[6].c = _60.m3s[6].c;
     ssbo_430.content.m3s[7].c = _60.m3s[7].c;
-    ssbo_430.content.m1.a = ssbo_430.content.m3.a * float2x3(ssbo_430.m6[1][1]);
+    ssbo_430.content.m1.a = ssbo_430.content.m3.a * ssbo_430.m6[1][1];
 }
 

reference/opt/shaders-msl/vert/packed_matrix.vert

@@ -41,7 +41,7 @@ vertex main0_out main0(main0_in in [[stage_in]], constant _42& _44 [[buffer(12)]
 {
     main0_out out = {};
     float4 _70 = _44._m0 * float4(float3(_44._m3) + (in.m_25.xyz * (_44._m6 + _44._m7)), 1.0);
-    out.m_72 = normalize(float4(in.m_25.xyz, 0.0) * float4x3(_17._m1));
+    out.m_72 = normalize(float4(in.m_25.xyz, 0.0) * _17._m1);
     float4 _95 = _70;
     _95.y = -_70.y;
     out.gl_Position = _95;

reference/shaders-msl/comp/struct-packing.comp

@@ -144,6 +144,6 @@ kernel void main0(device SSBO0& ssbo_140 [[buffer(0)]], device SSBO1& ssbo_430 [
     ssbo_430.content.m3s[5].c = _60.m3s[5].c;
     ssbo_430.content.m3s[6].c = _60.m3s[6].c;
     ssbo_430.content.m3s[7].c = _60.m3s[7].c;
-    ssbo_430.content.m1.a = ssbo_430.content.m3.a * float2x3(ssbo_430.m6[1][1]);
+    ssbo_430.content.m1.a = ssbo_430.content.m3.a * ssbo_430.m6[1][1];
 }
 

reference/shaders-msl/vert/packed_matrix.vert

@@ -44,7 +44,7 @@ vertex main0_out main0(main0_in in [[stage_in]], constant _42& _44 [[buffer(12)]
     float3 _13;
     do
     {
-        _13 = normalize(float4(in.m_25.xyz, 0.0) * float4x3(_17._m1));
+        _13 = normalize(float4(in.m_25.xyz, 0.0) * _17._m1);
         break;
     } while (false);
     float4 _39 = _44._m0 * float4(float3(_44._m3) + (in.m_25.xyz * (_44._m6 + _44._m7)), 1.0);

spirv_glsl.cpp

@@ -2375,7 +2375,10 @@ string CompilerGLSL::to_enclosed_expression(uint32_t id)
 
 string CompilerGLSL::to_unpacked_expression(uint32_t id)
 {
-	if (has_decoration(id, DecorationCPacked))
+	// If we need to transpose, it will also take care of unpacking rules.
+	auto *e = maybe_get<SPIRExpression>(id);
+	bool need_transpose = e && e->need_transpose;
+	if (!need_transpose && has_decoration(id, DecorationCPacked))
 		return unpack_expression_type(to_expression(id), expression_type(id));
 	else
 		return to_expression(id);
@@ -2383,7 +2386,10 @@ string CompilerGLSL::to_unpacked_expression(uint32_t id)
 
 string CompilerGLSL::to_enclosed_unpacked_expression(uint32_t id)
 {
-	if (has_decoration(id, DecorationCPacked))
+	// If we need to transpose, it will also take care of unpacking rules.
+	auto *e = maybe_get<SPIRExpression>(id);
+	bool need_transpose = e && e->need_transpose;
+	if (!need_transpose && has_decoration(id, DecorationCPacked))
 		return unpack_expression_type(to_expression(id), expression_type(id));
 	else
 		return to_enclosed_expression(id);

spirv_msl.cpp

@@ -2042,7 +2042,16 @@ void CompilerMSL::emit_instruction(const Instruction &instruction)
 		if (e && e->need_transpose && (t.columns == t.vecsize || is_packed))
 		{
 			e->need_transpose = false;
+
+			// This is important for matrices. Packed matrices
+			// are generally transposed, so unpacking using a constructor argument
+			// will result in an error.
+			// The simplest solution for now is to just avoid unpacking the matrix in this operation.
+			unset_decoration(mtx_id, DecorationCPacked);
+
 			emit_binary_op(ops[0], ops[1], ops[3], ops[2], "*");
+			if (is_packed)
+				set_decoration(mtx_id, DecorationCPacked);
 			e->need_transpose = true;
 		}
 		else