From b32280baf9ef46cc0c9f1c700af4fd5c4e1e9acb Mon Sep 17 00:00:00 2001
From: Tim Northover <tnorthover@apple.com>
Date: Tue, 22 Nov 2022 11:27:05 +0000
Subject: [PATCH] X86: relax EFLAGS liveness check when generating stack
 probes.

The probes are all inserted at the iterator passed into the functions, so
that's where any EFLAGS clobbering will happen and where we need it to be dead.

Fixes: https://github.com/llvm/llvm-project/issues/59121
---
 llvm/lib/Target/X86/X86FrameLowering.cpp    |  9 ++++---
 llvm/test/CodeGen/X86/probe-stack-eflags.ll | 37 +++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+), 3 deletions(-)

diff --git a/llvm/lib/Target/X86/X86FrameLowering.cpp b/llvm/lib/Target/X86/X86FrameLowering.cpp
index b6fa3d5..2f1f21f 100644
--- a/llvm/lib/Target/X86/X86FrameLowering.cpp
+++ b/llvm/lib/Target/X86/X86FrameLowering.cpp
@@ -733,7 +733,8 @@ void X86FrameLowering::emitStackProbeInlineGenericLoop(
     uint64_t AlignOffset) const {
   assert(Offset && "null offset");
 
-  assert(!MBB.isLiveIn(X86::EFLAGS) &&
+  assert(MBB.computeRegisterLiveness(TRI, X86::EFLAGS, MBBI) !=
+             MachineBasicBlock::LQR_Live &&
          "Inline stack probe loop will clobber live EFLAGS.");
 
   const bool NeedsDwarfCFI = needsDwarfCFI(MF);
@@ -873,7 +874,8 @@ void X86FrameLowering::emitStackProbeInlineWindowsCoreCLR64(
   const TargetInstrInfo &TII = *STI.getInstrInfo();
   const BasicBlock *LLVM_BB = MBB.getBasicBlock();
 
-  assert(!MBB.isLiveIn(X86::EFLAGS) &&
+  assert(MBB.computeRegisterLiveness(TRI, X86::EFLAGS, MBBI) !=
+             MachineBasicBlock::LQR_Live &&
          "Inline stack probe loop will clobber live EFLAGS.");
 
   // RAX contains the number of bytes of desired stack adjustment.
@@ -1112,7 +1114,8 @@ void X86FrameLowering::emitStackProbeCall(
     report_fatal_error("Emitting stack probe calls on 64-bit with the large "
                        "code model and indirect thunks not yet implemented.");
 
-  assert(!MBB.isLiveIn(X86::EFLAGS) &&
+  assert(MBB.computeRegisterLiveness(TRI, X86::EFLAGS, MBBI) !=
+             MachineBasicBlock::LQR_Live &&
          "Stack probe calls will clobber live EFLAGS.");
 
   unsigned CallOp;
diff --git a/llvm/test/CodeGen/X86/probe-stack-eflags.ll b/llvm/test/CodeGen/X86/probe-stack-eflags.ll
index 28432ef..cc1839b 100644
--- a/llvm/test/CodeGen/X86/probe-stack-eflags.ll
+++ b/llvm/test/CodeGen/X86/probe-stack-eflags.ll
@@ -75,4 +75,41 @@ exit2: ; preds = %bb70.i, %bb13.i
   ret i32 %.1.i
 }
 
+define void @CSE_eflags_live(i64 %length) "probe-stack"="__chkstk_darwin" {
+; CHECK-LABEL: CSE_eflags_live:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    pushq %rbp
+; CHECK-NEXT:    .cfi_def_cfa_offset 16
+; CHECK-NEXT:    .cfi_offset %rbp, -16
+; CHECK-NEXT:    movq %rsp, %rbp
+; CHECK-NEXT:    .cfi_def_cfa_register %rbp
+; CHECK-NEXT:    testq %rdi, %rdi
+; CHECK-NEXT:    je .LBB1_2
+; CHECK-NEXT:  # %bb.1: # %if.end6
+; CHECK-NEXT:    movq $-1, %rax
+; CHECK-NEXT:    cmovnsq %rdi, %rax
+; CHECK-NEXT:    addq $15, %rax
+; CHECK-NEXT:    andq $-16, %rax
+; CHECK-NEXT:    callq __chkstk_darwin
+; CHECK-NEXT:    subq %rax, %rsp
+; CHECK-NEXT:  .LBB1_2: # %cleanup78
+; CHECK-NEXT:    movq %rbp, %rsp
+; CHECK-NEXT:    popq %rbp
+; CHECK-NEXT:    .cfi_def_cfa %rsp, 8
+; CHECK-NEXT:    retq
+entry:
+  %cmp4 = icmp eq i64 %length, 0
+  br i1 %cmp4, label %cleanup78, label %if.end6
+
+if.end6:
+  %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 = { nounwind "probe-stack"="inline-asm" }
-- 
2.7.4