Add support for `-fvk-invert-y`. (#3012)

Co-authored-by: Yong He <yhe@nvidia.com>

9 files changed, 126 insertions, 1 deletions

diff --git a/source/slang/slang-emit.cpp b/source/slang/slang-emit.cpp
index 6a43ff8c2..8f4d68a75 100644
--- a/source/slang/slang-emit.cpp
+++ b/source/slang/slang-emit.cpp
@@ -63,6 +63,7 @@
 #include "slang-ir-string-hash.h"
 #include "slang-ir-simplify-for-emit.h"
 #include "slang-ir-pytorch-cpp-binding.h"
+#include "slang-ir-vk-invert-y.h"
 #include "slang-legalize-types.h"
 #include "slang-lower-to-ir.h"
 #include "slang-mangle.h"
@@ -864,6 +865,8 @@ Result linkAndOptimizeIR(
     if (isKhronosTarget(targetRequest) || target == CodeGenTarget::HLSL)
     {
         legalizeUniformBufferLoad(irModule);
+        if (targetRequest->getHLSLToVulkanLayoutOptions() && targetRequest->getHLSLToVulkanLayoutOptions()->shouldInvertY())
+            invertYOfPositionOutput(irModule);
     }
 
     // Lower sizeof/alignof
diff --git a/source/slang/slang-hlsl-to-vulkan-layout-options.cpp b/source/slang/slang-hlsl-to-vulkan-layout-options.cpp
index 74a3313da..1c0e0858b 100644
--- a/source/slang/slang-hlsl-to-vulkan-layout-options.cpp
+++ b/source/slang/slang-hlsl-to-vulkan-layout-options.cpp
@@ -91,7 +91,7 @@ Index HLSLToVulkanLayoutOptions::getShift(Kind kind, Index set) const
 
 bool HLSLToVulkanLayoutOptions::hasState() const
 {
-    return canInferBindings() || hasGlobalsBinding();
+    return canInferBindings() || hasGlobalsBinding() || shouldInvertY();
 }
 
 HLSLToVulkanLayoutOptions::Binding HLSLToVulkanLayoutOptions::inferBinding(Kind kind, const Binding& inBinding) const
diff --git a/source/slang/slang-hlsl-to-vulkan-layout-options.h b/source/slang/slang-hlsl-to-vulkan-layout-options.h
index e16989810..4ae169d90 100644
--- a/source/slang/slang-hlsl-to-vulkan-layout-options.h
+++ b/source/slang/slang-hlsl-to-vulkan-layout-options.h
@@ -116,6 +116,9 @@ public:
         /// True if can infer a binding for a kind
     bool canInferBindingForKind(Kind kind) const { return (m_kindShiftEnabledFlags & getKindFlag(kind)) != 0; }
 
+        /// True if the compiler should invert the Y coordinate of any SV_Position output.
+    bool shouldInvertY() const { return m_invertY; }
+
         /// Given an kind and a binding infer the vulkan binding.
         /// Will return an invalid binding if one is not found
     Binding inferBinding(Kind kind, const Binding& inBinding) const;
@@ -140,6 +143,8 @@ public:
         /// Get the globals binding
     const Binding& getGlobalsBinding() const { return m_globalsBinding; }
 
+    void setInvertY(bool value) { m_invertY = value; }
+
         /// Ctor
     HLSLToVulkanLayoutOptions();
     
@@ -163,6 +168,9 @@ protected:
 
         /// Maps a key to the amount of shift
     Dictionary<Key, Index> m_shifts;
+
+        /// Whether to invert the Y coordinate of SV_Position output.
+    bool m_invertY = false;
 };
 
 } // namespace Slang
diff --git a/source/slang/slang-ir-glsl-legalize.cpp b/source/slang/slang-ir-glsl-legalize.cpp
index 54eaa67a5..dfe370d2b 100644
--- a/source/slang/slang-ir-glsl-legalize.cpp
+++ b/source/slang/slang-ir-glsl-legalize.cpp
@@ -319,6 +319,12 @@ struct GlobalVaryingDeclarator
     GlobalVaryingDeclarator*    next;
 };
 
+enum GLSLSystemValueKind
+{
+    General,
+    PositionOutput,
+};
+
 struct GLSLSystemValueInfo
 {
     // The name of the built-in GLSL variable
@@ -334,6 +340,9 @@ struct GLSLSystemValueInfo
     // If the built in GLSL variable is an array, holds the index into the array.
     // If < 0, then there is no array indexing
     Index arrayIndex;
+
+    // The kind of the system value that requires special treatment.
+    GLSLSystemValueKind kind = GLSLSystemValueKind::General;
 };
 
 static void leafAddressesImpl(List<IRInst*>& ret, const ScalarizedVal& v)
@@ -511,6 +520,7 @@ GLSLSystemValueInfo* getGLSLSystemValueInfo(
     char const* name = nullptr;
     char const* outerArrayName = nullptr;
     int arrayIndex = -1;
+    GLSLSystemValueKind systemValueKind = GLSLSystemValueKind::General;
 
     auto semanticInst = varLayout->findSystemValueSemanticAttr();
     if(!semanticInst)
@@ -558,6 +568,10 @@ GLSLSystemValueInfo* getGLSLSystemValueInfo(
         else
         {
             name = "gl_Position";
+            if (kind == LayoutResourceKind::VaryingOutput)
+            {
+                systemValueKind = GLSLSystemValueKind::PositionOutput;
+            }
         }
 
         requiredType = builder->getVectorType(builder->getBasicType(BaseType::Float), builder->getIntValue(builder->getIntType(), 4));
@@ -918,6 +932,7 @@ GLSLSystemValueInfo* getGLSLSystemValueInfo(
         inStorage->outerArrayName = outerArrayName;
         inStorage->requiredType = requiredType;
         inStorage->arrayIndex = arrayIndex;
+        inStorage->kind = systemValueKind;
         return inStorage;
     }
 
@@ -1160,6 +1175,15 @@ ScalarizedVal createSimpleGLSLGlobalVarying(
         {
             builder->addGLSLOuterArrayDecoration(globalParam, UnownedTerminatedStringSlice(outerArrayName));
         }
+
+        switch (systemValueInfo->kind)
+        {
+        case GLSLSystemValueKind::PositionOutput:
+            builder->addGLPositionOutputDecoration(globalParam);
+            break;
+        default:
+            break;
+        }
     }
 
     if(declarator && declarator->flavor == GlobalVaryingDeclarator::Flavor::meshOutputPrimitives)
diff --git a/source/slang/slang-ir-inst-defs.h b/source/slang/slang-ir-inst-defs.h
index 231ae6dbe..4716ed427 100644
--- a/source/slang/slang-ir-inst-defs.h
+++ b/source/slang/slang-ir-inst-defs.h
@@ -795,6 +795,9 @@ INST(HighLevelDeclDecoration,               highLevelDecl,          1, 0)
     INST_RANGE(MeshOutputDecoration, VerticesDecoration, PrimitivesDecoration)
     INST(GLSLPrimitivesRateDecoration, perprimitive, 0, 0)
 
+        // Marks an inst that represents the gl_Position output.
+    INST(GLPositionOutputDecoration, PositionOutput, 0, 0)
+
     /* StageAccessDecoration */
         INST(StageReadAccessDecoration, stageReadAccess, 0, 0)
         INST(StageWriteAccessDecoration, stageWriteAccess, 0, 0)
diff --git a/source/slang/slang-ir-insts.h b/source/slang/slang-ir-insts.h
index 417b39da3..2312cc4f2 100644
--- a/source/slang/slang-ir-insts.h
+++ b/source/slang/slang-ir-insts.h
@@ -1213,6 +1213,11 @@ struct IRGLSLPrimitivesRateDecoration : public IRDecoration
     IR_LEAF_ISA(GLSLPrimitivesRateDecoration)
 };
 
+struct IRGLPositionOutputDecoration : public IRDecoration
+{
+    IR_LEAF_ISA(GLPositionOutputDecoration)
+};
+
 struct IRMeshOutputRef : public IRInst
 {
     enum { kOp = kIROp_MeshOutputRef };
@@ -3815,6 +3820,11 @@ public:
         addDecoration(value, kIROp_GLSLOuterArrayDecoration, getStringValue(text));
     }
 
+    void addGLPositionOutputDecoration(IRInst* value)
+    {
+        addDecoration(value, kIROp_GLPositionOutputDecoration);
+    }
+
     void addInterpolationModeDecoration(IRInst* value, IRInterpolationMode mode)
     {
         addDecoration(value, kIROp_InterpolationModeDecoration, getIntValue(getIntType(), IRIntegerValue(mode)));
diff --git a/source/slang/slang-ir-vk-invert-y.cpp b/source/slang/slang-ir-vk-invert-y.cpp
new file mode 100644
index 000000000..5c21fee95
--- /dev/null
+++ b/source/slang/slang-ir-vk-invert-y.cpp
@@ -0,0 +1,59 @@
+#include "slang-ir-vk-invert-y.h"
+#include "slang-ir.h"
+#include "slang-ir-insts.h"
+
+namespace Slang
+{
+
+static IRInst* _invertYOfVector(IRBuilder& builder, IRInst* originalVector)
+{
+    auto vectorType = as<IRVectorType>(originalVector->getDataType());
+    SLANG_ASSERT(vectorType);
+    UInt elementIndexY = 1;
+    auto originalY = builder.emitSwizzle(vectorType->getElementType(), originalVector, 1, &elementIndexY);
+    auto negY = builder.emitNeg(originalY->getDataType(), originalY);
+    auto newVal = builder.emitSwizzleSet(originalVector->getDataType(), originalVector, negY, 1, &elementIndexY);
+    return newVal;
+}
+// Find outputs to SV_Position and invert the y coordinates of it right before the write.
+void invertYOfPositionOutput(IRModule* module)
+{
+    for (auto globalInst : module->getGlobalInsts())
+    {
+        if (globalInst->findDecoration<IRGLPositionOutputDecoration>())
+        {
+            // Find all loads and stores to it.
+            IRBuilder builder(module);
+            traverseUses(globalInst, [&](IRUse* use)
+                {
+                    if (auto store = as<IRStore>(use->getUser()))
+                    {
+                        if (store->getPtr() != globalInst)
+                            return;
+
+                        builder.setInsertBefore(store);
+                        auto originalVal = store->getVal();
+                        auto invertedVal = _invertYOfVector(builder, originalVal);
+                        builder.replaceOperand(&store->val, invertedVal);
+                    }
+                    else if (auto load = as<IRLoad>(use->getUser()))
+                    {
+                        // Since we negate the y coordinate before writing
+                        // to gl_Position, we also need to negate the value after reading from it.
+                        builder.setInsertAfter(load);
+                        // Store existing uses of the load that we are going to replace with inverted val later.
+                        List<IRUse*> oldUses;
+                        for (auto loadUse = load->firstUse; loadUse; loadUse = loadUse->nextUse)
+                            oldUses.add(loadUse);
+                        // Get the inverted vector.
+                        auto invertedVal = _invertYOfVector(builder, load);
+                        // Replace original uses with the invertex vector.
+                        for (auto loadUse : oldUses)
+                            builder.replaceOperand(loadUse, invertedVal);
+                    }
+                });
+        }
+    }
+}
+
+}
diff --git a/source/slang/slang-ir-vk-invert-y.h b/source/slang/slang-ir-vk-invert-y.h
new file mode 100644
index 000000000..b6b1e4a4c
--- /dev/null
+++ b/source/slang/slang-ir-vk-invert-y.h
@@ -0,0 +1,10 @@
+#ifndef SLANG_IR_VK_INVERT_Y_H
+#define SLANG_IR_VK_INVERT_Y_H
+
+namespace Slang
+{
+    struct IRModule;
+    void invertYOfPositionOutput(IRModule* module);
+}
+
+#endif
diff --git a/source/slang/slang-options.cpp b/source/slang/slang-options.cpp
index dd4473497..e59109b37 100644
--- a/source/slang/slang-options.cpp
+++ b/source/slang/slang-options.cpp
@@ -92,6 +92,7 @@ enum class OptionKind
 
     VulkanBindShift,
     VulkanBindGlobals,
+    VulkanInvertY,
 
     GLSLForceScalarLayout,
     EnableEffectAnnotations,
@@ -496,6 +497,7 @@ void initCommandOptions(CommandOptions& options)
         "* [GLSL wiki](https://github.com/KhronosGroup/glslang/wiki/HLSL-FAQ#auto-mapped-binding-numbers)\n" },
         { OptionKind::VulkanBindGlobals, "-fvk-bind-globals", "-fvk-bind-globals <N> <descriptor-set>",
         "Places the $Globals cbuffer at descriptor set <descriptor-set> and binding <N>."},
+        { OptionKind::VulkanInvertY, "-fvk-invert-y", nullptr, "Negates (additively inverts) SV_Position.y before writing to stage output."},
         { OptionKind::EnableEffectAnnotations,
          "-enable-effect-annotations", nullptr, 
          "Enables support for legacy effect annotation syntax."},
@@ -2008,6 +2010,12 @@ SlangResult OptionsParser::_parse(
                 m_hlslToVulkanLayoutOptions->setGlobalsBinding(Index(bindingSet), Index(binding));
                 break;
             }
+            case OptionKind::VulkanInvertY:
+            {
+                // -fvk-invert-y
+                m_hlslToVulkanLayoutOptions->setInvertY(true);
+                break;
+            }
             case OptionKind::Profile: SLANG_RETURN_ON_FAIL(_parseProfile(arg)); break;
             case OptionKind::Capability:
             {