If we have a DYN_ALLOCA_* instruction, it will eventually be expanded to a stack probe and subtract-from-SP. Add debug-info instrumentation to X86FrameLowering::emitStackProbe so that it can redirect debug-info for the DYN_ALLOCA to the lowered stack probe.
In practice, this means putting an instruction number label either the call instruction to _chkstk for win32, or more commonly on the subtract from SP instruction. The two tests added cover both of these cases.
- I don't think there are any paths with the Large code-model and 64-bit Windows that will use the NumCallOps number, because it's only win32 that uses _chkstck to modify SP,
- There are other code paths from emitStackProbe that implement probes, such as emitStackProbeInline, but I believe they all deal with fixed-size allocations in the prologue, and so aren't of interest to lowered DYN_ALLOCA instructions
(Adding Craig as this touches X86 things)