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Fix a critical bug in 64-bit atomic operation lowering for 32-bit. The results of the cmpxchg8b instructions are being thrown away when it branches back to the top of the checking loop. This means the loop always compares against the old value and this can result in a dead lock.

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llvm-svn: 93028
This commit is contained in:
Evan Cheng 2010-01-08 23:41:50 +00:00
parent 79200db8b8
commit 2e497d1ed4
2 changed files with 39 additions and 8 deletions
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18
lib/Target/X86/X86ISelLowering.cpp
View File

@ -7831,14 +7831,16 @@ X86TargetLowering::EmitAtomicBit6432WithCustomInserter(MachineInstr *bInstr,
BuildMI(newMBB, dl, TII->get(X86::PHI), dest2Oper.getReg())
.addReg(t2).addMBB(thisMBB).addReg(t4).addMBB(newMBB);
unsigned tt1 = F->getRegInfo().createVirtualRegister(RC);
unsigned tt2 = F->getRegInfo().createVirtualRegister(RC);
// The subsequent operations should be using the destination registers of
//the PHI instructions.
if (invSrc) {
MIB = BuildMI(newMBB, dl, TII->get(NotOpc), tt1).addReg(t1);
MIB = BuildMI(newMBB, dl, TII->get(NotOpc), tt2).addReg(t2);
t1 = F->getRegInfo().createVirtualRegister(RC);
t2 = F->getRegInfo().createVirtualRegister(RC);
MIB = BuildMI(newMBB, dl, TII->get(NotOpc), t1).addReg(dest1Oper.getReg());
MIB = BuildMI(newMBB, dl, TII->get(NotOpc), t2).addReg(dest2Oper.getReg());
} else {
tt1 = t1;
tt2 = t2;
t1 = dest1Oper.getReg();
t2 = dest2Oper.getReg();
}
int valArgIndx = lastAddrIndx + 1;
@ -7852,7 +7854,7 @@ X86TargetLowering::EmitAtomicBit6432WithCustomInserter(MachineInstr *bInstr,
else
MIB = BuildMI(newMBB, dl, TII->get(immOpcL), t5);
if (regOpcL != X86::MOV32rr)
MIB.addReg(tt1);
MIB.addReg(t1);
(*MIB).addOperand(*argOpers[valArgIndx]);
assert(argOpers[valArgIndx + 1]->isReg() ==
argOpers[valArgIndx]->isReg());
@ -7863,7 +7865,7 @@ X86TargetLowering::EmitAtomicBit6432WithCustomInserter(MachineInstr *bInstr,
else
MIB = BuildMI(newMBB, dl, TII->get(immOpcH), t6);
if (regOpcH != X86::MOV32rr)
MIB.addReg(tt2);
MIB.addReg(t2);
(*MIB).addOperand(*argOpers[valArgIndx + 1]);
MIB = BuildMI(newMBB, dl, TII->get(copyOpc), X86::EAX);

29
test/CodeGen/X86/2010-01-08-Atomic64Bug.ll Normal file
View File

@ -0,0 +1,29 @@
; RUN: llc < %s -mtriple=i386-apple-darwin | FileCheck %s
; rdar://r7512579
; PHI defs in the atomic loop should be used by the add / adc
; instructions. They should not be dead.
define void @t(i64* nocapture %p) nounwind ssp {
entry:
; CHECK: t:
; CHECK: movl $1
; CHECK: movl (%ebp), %eax
; CHECK: movl 4(%ebp), %edx
; CHECK: LBB1_1:
; CHECK-NOT: movl $1
; CHECK-NOT: movl $0
; CHECK: addl
; CHECK: adcl
; CHECK: lock
; CHECK: cmpxchg8b
; CHECK: jne
tail call void @llvm.memory.barrier(i1 true, i1 true, i1 true, i1 true, i1 true)
%0 = tail call i64 @llvm.atomic.load.add.i64.p0i64(i64* %p, i64 1) ; <i64> [#uses=0]
tail call void @llvm.memory.barrier(i1 true, i1 true, i1 true, i1 true, i1 true)
ret void
}
declare void @llvm.memory.barrier(i1, i1, i1, i1, i1) nounwind
declare i64 @llvm.atomic.load.add.i64.p0i64(i64* nocapture, i64) nounwind