Validation error when optimizations are enabled: `llvm.umul.with.overflow.i32` is not a DXIL function

[teoxoy]

Description
Encountered a DXIL validation error when optimizations are enabled. With -Od the shader compiles fine.

Steps to Reproduce
https://godbolt.org/z/hs5se5zzG

RWStructuredBuffer<uint> buf : register(u0);

[numthreads(1, 1, 1)]
void main()
{
    uint x = buf[0];
    uint y = buf[1];
    if (((uint64_t)x) * ((uint64_t)y) > 0xffffffffull) {
        buf[2] = 1;
    }
}

Ran via:

dxc.exe test.hlsl -E main -T cs_6_0

Actual Behavior

error: validation errors
test.hlsl:8:39: error: ExtractValue should only be used on dxil struct types and cmpxchg.
note: at '%7 = extractvalue { i32, i1 } %6, 1' in block '#0' of function 'main'.
Function: llvm.umul.with.overflow.i32: error: External function 'llvm.umul.with.overflow.i32' is not a DXIL function.
Validation failed.

Environment

• DXC version: v1.9.2602.24
• Host Operating System: Windows 11 26200.8655

[damyanp]

Repros on 1.6.2112 https://godbolt.org/z/rjW9Er1Tc