[llvm-bugs] [Bug 38376] New: X86FrameLowering::emitStackProbeInline does not preserve liveness information

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=38376

            Bug ID: 38376
           Summary: X86FrameLowering::emitStackProbeInline does not
                    preserve liveness information
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: francisvm at yahoo.com
                CC: llvm-bugs at lists.llvm.org

Created attachment 20622
  --> https://bugs.llvm.org/attachment.cgi?id=20622&action=edit
MIR test for 1) and 2).

See win.mir.

It fails with:

$ ./build/bin/llc -verify-machineinstrs win.mir -run-pass prologepilog
-mtriple=x86_64-pc-win32-coreclr                     *[master]

# After Prologue/Epilogue Insertion & Frame Finalization
# Machine code for function main4k: IsSSA, NoPHIs, TracksLiveness, NoVRegs
Frame Objects:
  fi#0: size=4096, align=1, at location [SP-4096]

bb.0.entry:
  successors: %bb.3(0x40000000), %bb.1(0x40000000); %bb.3(200.00%),
%bb.1(200.00%)

  $eax = frame-setup MOV32ri 4096
  frame-setup MOV64mr $rsp, 1, $noreg, 8, $noreg, $rcx
  frame-setup MOV64mr $rsp, 1, $noreg, 16, $noreg, $rdx
  $rcx = frame-setup XOR64rr undef $rcx, undef $rcx, implicit-def $eflags
  $rdx = frame-setup MOV64rr $rsp
  $rdx = frame-setup SUB64rr $rdx, $rax, implicit-def $eflags
  $rdx = frame-setup CMOVB64rr $rdx, $rcx, implicit $eflags
  $rcx = frame-setup MOV64rm $noreg, 1, $noreg, 16, $gs
  frame-setup CMP64rr $rdx, $rcx, implicit-def $eflags
  frame-setup JAE_1 %bb.3, implicit $eflags

bb.1.entry:
; predecessors: %bb.0
  successors: %bb.2(0x80000000); %bb.2(200.00%)

  $rdx = frame-setup AND64ri32 $rdx, -4096, implicit-def $eflags
  frame-setup JMP_1 %bb.2

bb.2.entry:
; predecessors: %bb.1, %bb.2
  successors: %bb.3(0x40000000), %bb.2(0x40000000); %bb.3(200.00%),
%bb.2(200.00%)

  $rcx = frame-setup LEA64r $rcx, 1, $noreg, -4096, $noreg
  frame-setup MOV8mi $rcx, 1, $noreg, 0, $noreg, 0
  frame-setup CMP64rr $rdx, $rcx, implicit-def $eflags
  frame-setup JNE_1 %bb.2, implicit $eflags

bb.3.entry:
; predecessors: %bb.0, %bb.2

  $rcx = frame-setup MOV64rm $rsp, 1, $noreg, 8, $noreg
  $rdx = frame-setup MOV64rm $rsp, 1, $noreg, 16, $noreg
  $rsp = frame-setup SUB64rr $rsp, $rax, implicit-def $eflags
  frame-setup SEH_StackAlloc 4096
  frame-setup SEH_EndPrologue
  $eax = IMPLICIT_DEF
  SEH_Epilogue
  $rsp = frame-destroy ADD64ri32 $rsp, 4096, implicit-def dead $eflags
  RET 0, killed $eax

# End machine code for function main4k.

*** Bad machine code: Using an undefined physical register ***
- function:    main4k
- basic block: %bb.0 entry (0x7fa418837478)
- instruction: frame-setup MOV64mr $rsp, 1, $noreg, 8, $noreg, $rcx
- operand 5:   $rcx

*** Bad machine code: Using an undefined physical register ***
- function:    main4k
- basic block: %bb.0 entry (0x7fa418837478)
- instruction: frame-setup MOV64mr $rsp, 1, $noreg, 16, $noreg, $rdx
- operand 5:   $rdx

*** Bad machine code: Using an undefined physical register ***
- function:    main4k
- basic block: %bb.1 entry (0x7fa4188379a8)
- instruction: $rdx = frame-setup AND64ri32 $rdx, -4096, implicit-def $eflags
- operand 1:   $rdx(tied-def 0)

*** Bad machine code: Using an undefined physical register ***
- function:    main4k
- basic block: %bb.2 entry (0x7fa418837a70)
- instruction: $rcx = frame-setup LEA64r $rcx, 1, $noreg, -4096, $noreg
- operand 1:   $rcx

*** Bad machine code: Using an undefined physical register ***
- function:    main4k
- basic block: %bb.2 entry (0x7fa418837a70)
- instruction: frame-setup CMP64rr $rdx, $rcx, implicit-def $eflags
- operand 0:   $rdx

*** Bad machine code: Using an undefined physical register ***
- function:    main4k
- basic block: %bb.3 entry (0x7fa418837b38)
- instruction: $rsp = frame-setup SUB64rr $rsp, $rax, implicit-def $eflags
- operand 2:   $rax
LLVM ERROR: Found 6 machine code errors.

There are multiple reasons this doesn't work properly:

1) The code always spills RCX and RDX if InProlog == true, which results in an
use of undefined phys reg.
2) FinalReg, JoinReg, RoundedReg, SizeReg are not added as live-ins to the
basic blocks that use them, therefore they are seen undefined.
3) The basic block (where the stack probe is inlined) is split in two: the
original block and the continue block. The liveins and the defs from the
original block are not propagated to the continue block when splitting.

For 1), checking if RCX and RDX are part of the MBB's liveins should be enough.
For 2), adding the registers to their MBB's liveins before the usage should be
enough.
For 3), I thought of using LivePhysRegs but I seem to be missing something as
it breaks somewhere else.

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