From 487ae034e2b03ddd67945132c8fecbd937952705 Mon Sep 17 00:00:00 2001
From: Sriram Murali <85252063+sriramm-nv@users.noreply.github.com>
Date: Mon, 13 May 2024 23:57:57 -0700
Subject: Add LoadAligned and StoreAligned methods to ByteAddressBuffers
 (#4066)

Fixes #4062

This change enables wide load/stores for byte-address-buffer backed
resources, when the data is accessed at an offset that is aligned.

**Goals**
- Improve performance by issuing wider instructions instead of sequence
  of scalar instructions, for load and stores of byte-address buffers.
- Reduce code-size and readability of the generated shaders.
- Help naive users as well as ninja programmers, generate optimal code.

**Non Goals**
- Help with Structured buffers, or other resources.
- Target compilation time improvements.

**Key changes**
Adds 2 new overloads for Load and Store operations on ByteAddress Buffers.
1. Load / Store with an extra alignment parameter
```
    resource.Load<T>(offset, alignment);
    resource.Store<T>(offset, value, alignment);
```
2. LoadAligned / StoreAligned with no extra parameter,
   with the same signature as orignial Load / Store.
```
    resource.LoadAligned<T>(offset);
    resource.StoreAligned<T>(offset, value);
```
    - This overload will implicitly identify the alignment value,
    from the base type T of the elementary unit of the resource.

**Supported resources**
1. Vectors
   This can be upto 4 elements, i.e. float -- float4.
2. Arrays
   This does not have a limit on number of elements, but on a
   conservative estimate, we can limit to few hundreds.
3. Structures
   This is used to group a resource of a single type.
```
 struct {
    float4 x;
 }
```
**Code updates**
- Modified byte-address-ir legalize to handle struct, array and vector
  kinds of load or store access
- Added custom hlsl stdlib functions to implement all the overloads for Load,
  Store etc.
- Added C-like emitter, SPIR-V emitter for handling ByteAddressBuffers.
- Added a new core stdlib function intrinsic to wrap around alignOf<T>().
- Added a new peephole optimization entry to identify the equivalent
  IntLiteral value from the alignOf<T>() inst.
- Added tests to check explicit, and implicit aligned Load and Store
  operations.
---
 source/slang/slang-emit-c-like.cpp | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

(limited to 'source/slang/slang-emit-c-like.cpp')

diff --git a/source/slang/slang-emit-c-like.cpp b/source/slang/slang-emit-c-like.cpp
index b44fa677c..19a7930f6 100644
--- a/source/slang/slang-emit-c-like.cpp
+++ b/source/slang/slang-emit-c-like.cpp
@@ -2674,6 +2674,7 @@ void CLikeSourceEmitter::defaultEmitInstExpr(IRInst* inst, const EmitOpInfo& inO
         break;
 
     case kIROp_ByteAddressBufferLoad:
+    {
         m_writer->emit("(");
         emitOperand(inst->getOperand(0), getInfo(EmitOp::General));
         m_writer->emit(").Load<");
@@ -2682,20 +2683,21 @@ void CLikeSourceEmitter::defaultEmitInstExpr(IRInst* inst, const EmitOpInfo& inO
         emitOperand(inst->getOperand(1), getInfo(EmitOp::General));
         m_writer->emit(")");
         break;
+    }
 
     case kIROp_ByteAddressBufferStore:
-        {
-            auto prec = getInfo(EmitOp::Postfix);
-            needClose = maybeEmitParens(outerPrec, prec);
+    {
+        auto prec = getInfo(EmitOp::Postfix);
+        needClose = maybeEmitParens(outerPrec, prec);
 
-            emitOperand(inst->getOperand(0), leftSide(outerPrec, prec));
-            m_writer->emit(".Store(");
-            emitOperand(inst->getOperand(1), getInfo(EmitOp::General));
-            m_writer->emit(",");
-            emitOperand(inst->getOperand(2), getInfo(EmitOp::General));
-            m_writer->emit(")");
-        }
+        emitOperand(inst->getOperand(0), leftSide(outerPrec, prec));
+        m_writer->emit(".Store(");
+        emitOperand(inst->getOperand(1), getInfo(EmitOp::General));
+        m_writer->emit(",");
+        emitOperand(inst->getOperand(inst->getOperandCount() - 1), getInfo(EmitOp::General));
+        m_writer->emit(")");
         break;
+    }
     case kIROp_PackAnyValue:
     {
         m_writer->emit("packAnyValue<");
-- 
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