Fix -fvk-invert-y (#7447)

#7446
This fixes some outdated documentation as well as a compile error when
enabling fvk-invert-y on lib files and makes sure that it only gets
enabled on SV_POSITION that is used in VS/GS/DS/MS (so PS doesn't get
caught in the crossfire).
Also tested the dx-position-w one and that one already has correct
behavior here.

---------

Co-authored-by: NielsbishereAlt <[email protected]>

Author: Nielsbishere

docs/SPIR-V.rst

@@ -4227,7 +4227,7 @@ codegen for Vulkan:
 - ``-fvk-use-dx-layout``: Uses DirectX layout rules for resources.
 - ``-fvk-invert-y``: Negates (additively inverts) SV_Position.y before writing
   to stage output. Used to accommodate the difference between Vulkan's
-  coordinate system and DirectX's. Only allowed in VS/DS/GS.
+  coordinate system and DirectX's. Only allowed in VS/DS/GS/MS/Lib.
 - ``-fvk-use-dx-position-w``: Reciprocates (multiplicatively inverts)
   SV_Position.w after reading from stage input. Used to accommodate the
   difference between Vulkan DirectX: the w component of SV_Position in PS is

include/dxc/Support/HLSLOptions.td

@@ -368,7 +368,7 @@ def fvk_bind_register : MultiArg<["-"], "fvk-bind-register", 4>, MetaVarName<"<t
   HelpText<"Specify Vulkan descriptor set and binding for a specific register">;
 def vkbr : MultiArg<["-"], "vkbr", 4>, Flags<[CoreOption, DriverOption]>, Alias<fvk_bind_register>;
 def fvk_invert_y: Flag<["-"], "fvk-invert-y">, Group<spirv_Group>, Flags<[CoreOption, DriverOption]>,
-  HelpText<"Negate SV_Position.y before writing to stage output in VS/DS/GS to accommodate Vulkan's coordinate system">;
+  HelpText<"Negate SV_Position.y before writing to stage output in VS/DS/GS/MS/Lib to accommodate Vulkan's coordinate system">;
 def fvk_use_dx_position_w: Flag<["-"], "fvk-use-dx-position-w">, Group<spirv_Group>, Flags<[CoreOption, DriverOption]>,
   HelpText<"Reciprocate SV_Position.w after reading from stage input in PS to accommodate the difference between Vulkan and DirectX">;
 def fvk_support_nonzero_base_instance: Flag<["-"], "fvk-support-nonzero-base-instance">, Group<spirv_Group>, Flags<[CoreOption, DriverOption]>,

tools/clang/lib/SPIRV/SpirvEmitter.cpp

@@ -604,8 +604,8 @@ SpirvEmitter::SpirvEmitter(CompilerInstance &ci)
     emitError("unknown shader module: %0", {}) << shaderModel->GetName();
 
   if (spirvOptions.invertY && !shaderModel->IsVS() && !shaderModel->IsDS() &&
-      !shaderModel->IsGS() && !shaderModel->IsMS())
-    emitError("-fvk-invert-y can only be used in VS/DS/GS/MS", {});
+      !shaderModel->IsGS() && !shaderModel->IsMS() && !shaderModel->IsLib())
+    emitError("-fvk-invert-y can only be used in VS/DS/GS/MS/Lib", {});
 
   if (spirvOptions.useGlLayout && spirvOptions.useDxLayout)
     emitError("cannot specify both -fvk-use-dx-layout and -fvk-use-gl-layout",
@@ -14964,8 +14964,12 @@ SpirvEmitter::createSpirvIntrInstExt(llvm::ArrayRef<const Attr *> attrs,
 SpirvInstruction *SpirvEmitter::invertYIfRequested(SpirvInstruction *position,
                                                    SourceLocation loc,
                                                    SourceRange range) {
-  // Negate SV_Position.y if requested
-  if (spirvOptions.invertY) {
+  // Negate SV_Position.y if requested and supported
+
+  bool supportsInvertY = spvContext.isVS() || spvContext.isGS() ||
+                         spvContext.isDS() || spvContext.isMS();
+
+  if (spirvOptions.invertY && supportsInvertY) {
     const auto oldY = spvBuilder.createCompositeExtract(
         astContext.FloatTy, position, {1}, loc, range);
     const auto newY = spvBuilder.createUnaryOp(

tools/clang/test/CodeGenSPIRV/vk.cloption.invert-y.lib.hlsl

@@ -0,0 +1,12 @@
+// RUN: %dxc -T lib_6_3 -fvk-invert-y -fcgl  %s -spirv | FileCheck %s
+
+[shader("vertex")]
+float4 main(float4 a : A) : SV_Position {
+    return a;
+}
+
+// CHECK:         [[a:%[0-9]+]] = OpFunctionCall %v4float %src_main %param_var_a
+// CHECK-NEXT: [[oldY:%[0-9]+]] = OpCompositeExtract %float [[a]] 1
+// CHECK-NEXT: [[newY:%[0-9]+]] = OpFNegate %float [[oldY]]
+// CHECK-NEXT:  [[pos:%[0-9]+]] = OpCompositeInsert %v4float [[newY]] [[a]] 1
+// CHECK-NEXT:                 OpStore %gl_Position [[pos]]