[DirectX] compute shader errors when indexing cbuffer matrix with non constant index.

[farzonl]

Description

Repro: https://hlsl.godbolt.org/z/bMx7vaE4j

A cbuffer matrix (float4x2) indexed via a dynamic index derived from SV_GroupIndex and writes to an RWStructuredBuffer causes The following error:

error: validation errors
<source>:9:15: error: Access to out-of-bounds memory is disallowed.
note: at '%12 = getelementptr inbounds [2 x float], [2 x float]* %3, i32 0, i32 2' in block '#0' of function 'main'.
Validation failed.

We do not see this error when targeting SPIR-V. Similarly Clang does not error on this same case
https://hlsl.godbolt.org/z/4W17rPrzv

[farzonl]

This is also producing the validation error (https://hlsl.godbolt.org/z/8fY3WT75E)

RWStructuredBuffer<float2> Out : register(u0);

cbuffer example : register(b1) {
    float4x2 M1;
};

[numthreads(1,1,1)]
void main() {
    for(int I = 0; I < 4; I++)
        Out[I] = M1[I];
}

But this is not (https://hlsl.godbolt.org/z/b5KTYhK4M)

RWStructuredBuffer<float2> Out0 : register(u0);
RWStructuredBuffer<float2> Out1 : register(u1);
RWStructuredBuffer<float2> Out2 : register(u2);
RWStructuredBuffer<float2> Out3 : register(u3);

cbuffer example : register(b4) {

    float4x2 M1;
};

[numthreads(1,1,1)]
void main() {
    Out0[0] = M1[0];
    Out1[0] = M1[1];
    Out2[0] = M1[2];
    Out3[0] = M1[3];
   
}