[DXIL] Compiler crashes when using optimizations and -Zi on a complex HLSL shader

[phlogios]

Commit 37e802c (May 20, 2021) breaks compilation of this shader, if optimizations are -O1, -O2 or -O3 AND -Zi is used. I found the breaking commit by using git bisect.

Remove any line from the shader at the bottom of this report and it will compile fine.
The crash happens here:

DL is nullptr at this point, which is not allowed.
I haven't been successful in tracking down the exact cause of the bug yet, but what I've found is that the above mentioned commit adds a change where some DebugLocs are set to nullptr if the LineNumber is 0. There's an optimization pass that does scalar replacement on matrix declarations SROAGlobalAndAllocas that creates a DebugLoc for each child created in the replacement, and that DebugLoc gets the same linenumber as the parent had (variable s3 in the shader), which is also zero. My investigation into this issue could misleading, I am not an expert on the workings of DXC.

static const float StaticConst1 = 0;
static const float StaticConst2 = 0;
static const float StaticConst3 = 0;
static const float StaticConst4 = 0;
static const float StaticConst5 = 0;
static const float StaticConst6 = 0;
static const float StaticConst7 = 0;
static const float StaticConst8 = 0;
static const float StaticConst9 = 0;
static const float StaticConst10 = 0;
static const float StaticConst11 = 0;
static const float StaticConst12 = 0;
static const float StaticConst13 = 0;
static const float StaticConst14 = 0;
static const float StaticConst15 = 0;
static const float StaticConst16 = 0;
static const float StaticConst17 = 0;
static const float StaticConst18 = 0;
static const float StaticConst19 = 0;
static const float StaticConst20 = 0;
static const float StaticConst21 = 0;
static const float StaticConst22 = 0;
static const float StaticConst23 = 0;
static const float StaticConst24 = 0;
static const float StaticConst25 = 0;
static const float StaticConst26 = 0;
static const float StaticConst27 = 0;
static const float StaticConst28 = 0;
static const float StaticConst29 = 0;
static const float StaticConst30 = 0;
static const float StaticConst31 = 0;
static const float StaticConst32 = 0;
static const float StaticConst33 = 0;
static const float StaticConst34 = 0;
static const float StaticConst35 = 0;
static const float StaticConst36 = 0;
static const float StaticConst37 = 0;
static const float StaticConst38 = 0;
static const float StaticConst39 = 0;

// Removing any of the above "fixes" the problem, but so does uncommenting these!
//static const float StaticConst40 = 0;
//static const float StaticConst41 = 0;
//static const float StaticConst42 = 0;
//static const float StaticConst43 = 0;
//static const float StaticConst44 = 0;
//static const float StaticConst45 = 0;

StructuredBuffer<float> Buf;

float calculateSomething(float a, float b, float c, float d)
{
    return 0;
}

float4x4 createMatrix(StructuredBuffer<float> buffer, float otherParam)
{
    float v1 = calculateSomething(0, 0, 0, 0);
    float v2 = calculateSomething(0, 0, 0, 0);
    float v3 = 0;
    float v4 = 0;
    float v5 = 0;
    float v6 = 0;
    float v7 = 0;
    float v8 = 0;
    float v9 = 0;
    float v10 = 0;
    // Removing any of the above "fixes" the problem, but so does uncommenting these!
    //float v11 = 0;
    //float v12 = 0;
    //float v13 = 0;
    return 0;
}

float4x4 getMatrix()
{
    return createMatrix(Buf, 0);
}

void doNothing(float param) { }

struct NestedStruct1
{
    float4x4 matrixMember;

    void init()
    {
        getMatrix();
        matrixMember = getMatrix();
    }
};

struct NestedStruct2
{
    NestedStruct1 nested1;
    float2x2 otherMember;
    void setNested1(NestedStruct1 val) { nested1 = val; }
};

struct NestedStruct3
{
    NestedStruct2 nested2;
    void setNested2(NestedStruct2 val) { nested2 = val; }
};

struct NestedStruct4
{
    NestedStruct3 nested3;
    void setNested3(NestedStruct3 val) { nested3 = val; }
};

void main(
    float In0 : TEXCOORD0,
    float In1 : TEXCOORD1,
    float In2 : TEXCOORD2,
    float In3 : TEXCOORD3,
    out float4 Position : SV_Position)
{
    NestedStruct4 s4;
    NestedStruct3 s3;
    NestedStruct2 s2;
    NestedStruct1 s1;

    doNothing(0);
    doNothing(0);
    doNothing(0);
    doNothing(0);
    doNothing(0);
    doNothing(0);
    doNothing(0);

    s1.init();
    s2.setNested1(s1);
    s3.setNested2(s2);
    s4.setNested3(s3);

    Position = 0;
}

[simontaylor81]

Is it possible to get some traction on this issue. It is completely blocking us (i.e. EA Frostbite) from updating DXC beyond our very old current version.