Implement `-fvk-use-dx-layout` (#4912)

* Implement `-fvk-use-dx-layout`

Fixes: #4126

Changes:
* Added fvk-use-dx-layout
* Modified `HLSLConstantBufferLayoutRulesImpl` for correctness (ex: Array is always 16 byte aligned)
* Added kFXCShaderResourceLayoutRulesFamilyImpl and kFXCConstantBufferLayoutRulesFamilyImpl to handle fvk-use-dx-layout
* Added `ConstantBufferLayoutRules` to manage constant buffer rules
* Added `alignCompositeElementOfNonAggregate`/`alignCompositeElementOfAggregate` to handle forced alignment of composites for ConstantBuffers
* `StructuredBuffer` rules are mostly equal to `scalar` layout, not much was needed to be changed to support this behavior.

* seperate legacy constant buffer and how Slang does constant-buffer normally

* undo an addition

* remove accidental test

* Address review and fix

Address review and remove GLSL support since GLSL requires a seperate legalization (need to linearlize structs like with `legalizeMetalIR` to assign explicit offsets)

* comments

* remove aggregate and non-aggregate logic

We don't need this distinction for the logic

---------

Co-authored-by: Yong He <yonghe@outlook.com>

1 files changed, 35 insertions, 0 deletions

diff --git a/source/slang/slang-ir-layout.cpp b/source/slang/slang-ir-layout.cpp
index 6a4e9360a..3a2471930 100644
--- a/source/slang/slang-ir-layout.cpp
+++ b/source/slang/slang-ir-layout.cpp
@@ -443,6 +443,33 @@ struct NaturalLayoutRules : IRTypeLayoutRules
     }
 };
 
+struct ConstantBufferLayoutRules : IRTypeLayoutRules
+{
+    ConstantBufferLayoutRules()
+    {
+        ruleName = IRTypeLayoutRuleName::D3DConstantBuffer;
+    }
+
+    /// Next member only aligns to 16 if the next member is an array/matrix/struct
+    virtual IRSizeAndAlignment alignCompositeElement(IRSizeAndAlignment currentSize)
+    {
+        // Matrix/Array/Struct should be aligned on a new register
+        return IRSizeAndAlignment(currentSize.size, 16);
+    }
+
+    virtual IRIntegerValue adjustOffsetForNextAggregateMember(IRIntegerValue currentSize, IRIntegerValue lastElementAlignment)
+    {
+        SLANG_UNUSED(lastElementAlignment);
+        return currentSize;
+    }
+
+    virtual IRSizeAndAlignment getVectorSizeAndAlignment(IRSizeAndAlignment element, IRIntegerValue count)
+    {
+        IRIntegerValue countForAlignment = count;
+        return IRSizeAndAlignment((int)(element.size * count), (int)(element.size * countForAlignment));
+    }
+};
+
 struct Std430LayoutRules : IRTypeLayoutRules
 {
     Std430LayoutRules()
@@ -534,6 +561,13 @@ IRTypeLayoutRules* IRTypeLayoutRules::getNatural()
     static NaturalLayoutRules rules;
     return &rules;
 }
+
+IRTypeLayoutRules* IRTypeLayoutRules::getConstantBuffer()
+{
+    static ConstantBufferLayoutRules rules;
+    return &rules;
+}
+
 IRTypeLayoutRules* IRTypeLayoutRules::get(IRTypeLayoutRuleName name)
 {
     switch (name)
@@ -541,6 +575,7 @@ IRTypeLayoutRules* IRTypeLayoutRules::get(IRTypeLayoutRuleName name)
         case IRTypeLayoutRuleName::Std430: return getStd430();
         case IRTypeLayoutRuleName::Std140: return getStd140();
         case IRTypeLayoutRuleName::Natural: return getNatural();
+        case IRTypeLayoutRuleName::D3DConstantBuffer: return getConstantBuffer();
         default: return nullptr;
     }
 }