Assertion failed: (!MBB.isLiveIn(X86::EFLAGS) && "Stack probe calls will clobber live EFLAGS."), function emitStackProbeCall

[dcci]

% ./llc ./a.ll
Assertion failed: (!MBB.isLiveIn(X86::EFLAGS) && "Stack probe calls will clobber live EFLAGS."), function emitStackProbeCall, file X86FrameLowering.cpp, line 1116.
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
Stack dump:
0.	Program arguments: ./llc ./a.ll
1.	Running pass 'Function Pass Manager' on module './a.ll'.

% cat a.ll 
target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64h-apple-macosx13.0.0"

define void @patatino(i64 %length) #0 {
entry:
  %cmp4 = icmp eq i64 %length, 0
  br i1 %cmp4, label %cleanup78, label %if.end6

if.end6:                                          ; preds = %entry
  %0 = tail call i64 @llvm.smax.i64(i64 %length, i64 -1)
  %vla = alloca i8, i64 %0, align 16
  br label %cleanup78

cleanup78:
  ret void
}

declare i64 @llvm.smax.i64(i64, i64)
attributes #0 = { "probe-stack"="__chkstk_darwin" }

[dcci]

cc: @RKSimon

[llvmbot]

@llvm/issue-subscribers-backend-x86

[TNorthover]

Looks like the assertion is a bit overzealous. It's inserting the call at a DYN_ALLOCA_64 later in the block so that's where the liveness of EFLAGS matters. That instruction is already marked as clobbering the register so it would be invalid MIR if it triggers, but that's what assertions are there to catch so that's fine.

[TNorthover]

Patch in review: https://reviews.llvm.org/D138486