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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.
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