Spurious warnings about duplicated loop indices

[jbarczak]

The example below emits spurious redefinition warnings about the loop iterator. It appears that permissive scoping rules are in use. This may be intentional, to match old compiler behavior, but if so, it might be better to hide it behind a compatibility switch, since C++ has moved past this.

uint g_count1;
uint g_count2;
Buffer<float4> Things;

float4 main() : SV_Target
{
	float4 data=0;
	for( uint i=0; i<g_count1; i++ )
	{
		data += Things[i];
	}

	for( uint i=0; i<g_count2; i++ )
	{
		data += Things[g_count1+i];
	}

	return data;
}

C:\scratch\hlsl.bin\Debug\bin>dxc -T ps_6_0 test.txt
test.txt:14:12: warning: redefinition of 'i' shadows declaration in the outer scope; most recent declaration will be used
        for( uint i=0; i<g_count2; i++ )
                  ^
test.txt:9:12: note: previous definition is here
        for( uint i=0; i<g_count1; i++ )
                  ^

[marcelolr]

Yes, this is there for compat. Now that we have versioning at the language level, this is one of the things we can do without. Thanks!

[Jasper-Bekkers]

@pow2clk Continuing the discussion from #4028 here, please consider either this for hlsl 2021, or consider having a "strict" mode in which applications that don't suffer this legacy can opt-out of this odd behavior since it's been leading to quite "interesting" bugs.

[TheRealMJP]

I agree with Jasper here, it would be really really really great if the behavior could be changed for HLSL 2021 (or if there were some way to opt into the expected behavior). We run into this all of the time in our shader code.