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Atomics: make use of the "cmpxchg weak" instruction.
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This also simplifies the IR we create slightly: instead of working out
where success & failure should go manually, it turns out we can just
always jump to a success/failure block created for the purpose. Later
phases will sort out the mess without much difficulty.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210917 91177308-0d34-0410-b5e6-96231b3b80d8
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@TNorthover
TNorthover committed Jun 13, 2014
1 parent 6b3ed2b commit 33fe993
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Showing 6 changed files with 232 additions and 48 deletions.
34 changes: 22 additions & 12 deletions lib/CodeGen/AtomicExpandLoadLinkedPass.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -243,19 +243,26 @@ bool AtomicExpandLoadLinked::expandAtomicCmpXchg(AtomicCmpXchgInst *CI) {
// %loaded = @load.linked(%addr)
// %should_store = icmp eq %loaded, %desired
// br i1 %should_store, label %cmpxchg.trystore,
// label %cmpxchg.end/%cmpxchg.barrier
// label %cmpxchg.failure
// cmpxchg.trystore:
// %stored = @store_conditional(%new, %addr)
// %try_again = icmp i32 ne %stored, 0
// br i1 %try_again, label %loop, label %cmpxchg.end
// cmpxchg.barrier:
// %success = icmp eq i32 %stored, 0
// br i1 %success, label %cmpxchg.success, label %loop/%cmpxchg.failure
// cmpxchg.success:
// fence?
// br label %cmpxchg.end
// cmpxchg.failure:
// fence?
// br label %cmpxchg.end
// cmpxchg.end:
// %success = phi i1 [true, %cmpxchg.success], [false, %cmpxchg.failure]
// %restmp = insertvalue { iN, i1 } undef, iN %loaded, 0
// %res = insertvalue { iN, i1 } %restmp, i1 %success, 1
// [...]
BasicBlock *ExitBB = BB->splitBasicBlock(CI, "cmpxchg.end");
auto BarrierBB = BasicBlock::Create(Ctx, "cmpxchg.barrier", F, ExitBB);
auto TryStoreBB = BasicBlock::Create(Ctx, "cmpxchg.trystore", F, BarrierBB);
auto FailureBB = BasicBlock::Create(Ctx, "cmpxchg.failure", F, ExitBB);
auto SuccessBB = BasicBlock::Create(Ctx, "cmpxchg.success", F, FailureBB);
auto TryStoreBB = BasicBlock::Create(Ctx, "cmpxchg.trystore", F, SuccessBB);
auto LoopBB = BasicBlock::Create(Ctx, "cmpxchg.start", F, TryStoreBB);

// This grabs the DebugLoc from CI
Expand All @@ -277,31 +284,34 @@ bool AtomicExpandLoadLinked::expandAtomicCmpXchg(AtomicCmpXchgInst *CI) {

// If the the cmpxchg doesn't actually need any ordering when it fails, we can
// jump straight past that fence instruction (if it exists).
BasicBlock *FailureBB = FailureOrder == Monotonic ? ExitBB : BarrierBB;
Builder.CreateCondBr(ShouldStore, TryStoreBB, FailureBB);

Builder.SetInsertPoint(TryStoreBB);
Value *StoreSuccess = TLI->emitStoreConditional(
Builder, CI->getNewValOperand(), Addr, MemOpOrder);
StoreSuccess = Builder.CreateICmpEQ(
StoreSuccess, ConstantInt::get(Type::getInt32Ty(Ctx), 0), "success");
Builder.CreateCondBr(StoreSuccess, BarrierBB, LoopBB);
Builder.CreateCondBr(StoreSuccess, SuccessBB,
CI->isWeak() ? FailureBB : LoopBB);

// Make sure later instructions don't get reordered with a fence if necessary.
Builder.SetInsertPoint(BarrierBB);
Builder.SetInsertPoint(SuccessBB);
insertTrailingFence(Builder, SuccessOrder);
Builder.CreateBr(ExitBB);

Builder.SetInsertPoint(FailureBB);
insertTrailingFence(Builder, FailureOrder);
Builder.CreateBr(ExitBB);

// Finally, we have control-flow based knowledge of whether the cmpxchg
// succeeded or not. We expose this to later passes by converting any
// subsequent "icmp eq/ne %loaded, %oldval" into a use of an appropriate PHI.

// Setup the builder so we can create any PHIs we need.
Builder.SetInsertPoint(FailureBB, FailureBB->begin());
BasicBlock *SuccessBB = FailureOrder == Monotonic ? BarrierBB : TryStoreBB;
Builder.SetInsertPoint(ExitBB, ExitBB->begin());
PHINode *Success = Builder.CreatePHI(Type::getInt1Ty(Ctx), 2);
Success->addIncoming(ConstantInt::getTrue(Ctx), SuccessBB);
Success->addIncoming(ConstantInt::getFalse(Ctx), LoopBB);
Success->addIncoming(ConstantInt::getFalse(Ctx), FailureBB);

// Look for any users of the cmpxchg that are just comparing the loaded value
// against the desired one, and replace them with the CFG-derived version.
Expand Down
5 changes: 3 additions & 2 deletions test/CodeGen/ARM/atomic-64bit.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -171,9 +171,10 @@ define i64 @test6(i64* %ptr, i64 %val) {

define i64 @test7(i64* %ptr, i64 %val1, i64 %val2) {
; CHECK-LABEL: test7:
; CHECK: dmb {{ish$}}
; CHECK-DAG: mov [[VAL1LO:r[0-9]+]], r1
; CHECK-DAG: dmb {{ish$}}
; CHECK: ldrexd [[REG1:(r[0-9]?[02468])]], [[REG2:(r[0-9]?[13579])]]
; CHECK-LE-DAG: eor [[MISMATCH_LO:r[0-9]+]], [[REG1]], r1
; CHECK-LE-DAG: eor [[MISMATCH_LO:r[0-9]+]], [[REG1]], [[VAL1LO]]
; CHECK-LE-DAG: eor [[MISMATCH_HI:r[0-9]+]], [[REG2]], r2
; CHECK-BE-DAG: eor [[MISMATCH_LO:r[0-9]+]], [[REG2]], r2
; CHECK-BE-DAG: eor [[MISMATCH_HI:r[0-9]+]], [[REG1]], r1
Expand Down
43 changes: 43 additions & 0 deletions test/CodeGen/ARM/cmpxchg-weak.ll
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Original file line number Diff line number Diff line change
@@ -0,0 +1,43 @@
; RUN: llc < %s -mtriple=armv7-apple-ios -verify-machineinstrs | FileCheck %s

define void @test_cmpxchg_weak(i32 *%addr, i32 %desired, i32 %new) {
; CHECK-LABEL: test_cmpxchg_weak:

%pair = cmpxchg weak i32* %addr, i32 %desired, i32 %new seq_cst monotonic
%oldval = extractvalue { i32, i1 } %pair, 0
; CHECK: dmb ish
; CHECK: ldrex [[LOADED:r[0-9]+]], [r0]
; CHECK: cmp [[LOADED]], r1
; CHECK: strexeq [[SUCCESS:r[0-9]+]], r2, [r0]
; CHECK: cmpeq [[SUCCESS]], #0
; CHECK: bne [[DONE:LBB[0-9]+_[0-9]+]]
; CHECK: dmb ish
; CHECK: [[DONE]]:
; CHECK: str r3, [r0]
; CHECK: bx lr

store i32 %oldval, i32* %addr
ret void
}


define i1 @test_cmpxchg_weak_to_bool(i32, i32 *%addr, i32 %desired, i32 %new) {
; CHECK-LABEL: test_cmpxchg_weak_to_bool:

%pair = cmpxchg weak i32* %addr, i32 %desired, i32 %new seq_cst monotonic
%success = extractvalue { i32, i1 } %pair, 1

; CHECK: dmb ish
; CHECK: mov r0, #0
; CHECK: ldrex [[LOADED:r[0-9]+]], [r1]
; CHECK: cmp [[LOADED]], r2
; CHECK: strexeq [[STATUS:r[0-9]+]], r3, [r1]
; CHECK: cmpeq [[STATUS]], #0
; CHECK: bne [[DONE:LBB[0-9]+_[0-9]+]]
; CHECK: dmb ish
; CHECK: mov r0, #1
; CHECK: [[DONE]]:
; CHECK: bx lr

ret i1 %success
}
48 changes: 32 additions & 16 deletions test/Transforms/AtomicExpandLoadLinked/ARM/atomic-expansion-v7.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -229,20 +229,24 @@ define i8 @test_cmpxchg_i8_seqcst_seqcst(i8* %ptr, i8 %desired, i8 %newval) {
; CHECK: [[OLDVAL32:%.*]] = call i32 @llvm.arm.ldrex.p0i8(i8* %ptr)
; CHECK: [[OLDVAL:%.*]] = trunc i32 %1 to i8
; CHECK: [[SHOULD_STORE:%.*]] = icmp eq i8 [[OLDVAL]], %desired
; CHECK: br i1 [[SHOULD_STORE]], label %[[TRY_STORE:.*]], label %[[BARRIER:.*]]
; CHECK: br i1 [[SHOULD_STORE]], label %[[TRY_STORE:.*]], label %[[FAILURE_BB:.*]]

; CHECK: [[TRY_STORE]]:
; CHECK: [[NEWVAL32:%.*]] = zext i8 %newval to i32
; CHECK: [[TRYAGAIN:%.*]] = call i32 @llvm.arm.strex.p0i8(i32 [[NEWVAL32]], i8* %ptr)
; CHECK: [[TST:%.*]] = icmp eq i32 [[TRYAGAIN]], 0
; CHECK: br i1 [[TST]], label %[[BARRIER:.*]], label %[[LOOP]]
; CHECK: br i1 [[TST]], label %[[SUCCESS_BB:.*]], label %[[LOOP]]

; CHECK: [[BARRIER]]:
; CHECK: [[SUCCESS:%.*]] = phi i1 [ true, %[[TRY_STORE]] ], [ false, %[[LOOP]] ]
; CHECK: [[SUCCESS_BB]]:
; CHECK: fence seq_cst
; CHECK: br label %[[DONE:.*]]

; CHECK: [[FAILURE_BB]]:
; CHECK: fence seq_cst
; CHECK: br label %[[DONE]]

; CHECK: [[DONE]]:
; CHECK: [[SUCCESS:%.*]] = phi i1 [ true, %[[SUCCESS_BB]] ], [ false, %[[FAILURE_BB]] ]
; CHECK: ret i8 [[OLDVAL]]

%pairold = cmpxchg i8* %ptr, i8 %desired, i8 %newval seq_cst seq_cst
Expand All @@ -259,20 +263,24 @@ define i16 @test_cmpxchg_i16_seqcst_monotonic(i16* %ptr, i16 %desired, i16 %newv
; CHECK: [[OLDVAL32:%.*]] = call i32 @llvm.arm.ldrex.p0i16(i16* %ptr)
; CHECK: [[OLDVAL:%.*]] = trunc i32 %1 to i16
; CHECK: [[SHOULD_STORE:%.*]] = icmp eq i16 [[OLDVAL]], %desired
; CHECK: br i1 [[SHOULD_STORE]], label %[[TRY_STORE:.*]], label %[[DONE:.*]]
; CHECK: br i1 [[SHOULD_STORE]], label %[[TRY_STORE:.*]], label %[[FAILURE_BB:.*]]

; CHECK: [[TRY_STORE]]:
; CHECK: [[NEWVAL32:%.*]] = zext i16 %newval to i32
; CHECK: [[TRYAGAIN:%.*]] = call i32 @llvm.arm.strex.p0i16(i32 [[NEWVAL32]], i16* %ptr)
; CHECK: [[TST:%.*]] = icmp eq i32 [[TRYAGAIN]], 0
; CHECK: br i1 [[TST]], label %[[BARRIER:.*]], label %[[LOOP]]
; CHECK: br i1 [[TST]], label %[[SUCCESS_BB:.*]], label %[[LOOP]]

; CHECK: [[BARRIER]]:
; CHECK: [[SUCCESS_BB]]:
; CHECK: fence seq_cst
; CHECK: br label %[[DONE:.*]]

; CHECK: [[FAILURE_BB]]:
; CHECK-NOT: fence
; CHECK: br label %[[DONE]]

; CHECK: [[DONE]]:
; CHECK: [[SUCCESS:%.*]] = phi i1 [ true, %[[BARRIER]] ], [ false, %[[LOOP]] ]
; CHECK: [[SUCCESS:%.*]] = phi i1 [ true, %[[SUCCESS_BB]] ], [ false, %[[FAILURE_BB]] ]
; CHECK: ret i16 [[OLDVAL]]

%pairold = cmpxchg i16* %ptr, i16 %desired, i16 %newval seq_cst monotonic
Expand All @@ -288,19 +296,23 @@ define i32 @test_cmpxchg_i32_acquire_acquire(i32* %ptr, i32 %desired, i32 %newva
; CHECK: [[LOOP]]:
; CHECK: [[OLDVAL:%.*]] = call i32 @llvm.arm.ldrex.p0i32(i32* %ptr)
; CHECK: [[SHOULD_STORE:%.*]] = icmp eq i32 [[OLDVAL]], %desired
; CHECK: br i1 [[SHOULD_STORE]], label %[[TRY_STORE:.*]], label %[[DONE:.*]]
; CHECK: br i1 [[SHOULD_STORE]], label %[[TRY_STORE:.*]], label %[[FAILURE_BB:.*]]

; CHECK: [[TRY_STORE]]:
; CHECK: [[TRYAGAIN:%.*]] = call i32 @llvm.arm.strex.p0i32(i32 %newval, i32* %ptr)
; CHECK: [[TST:%.*]] = icmp eq i32 [[TRYAGAIN]], 0
; CHECK: br i1 [[TST]], label %[[BARRIER:.*]], label %[[LOOP]]
; CHECK: br i1 [[TST]], label %[[SUCCESS_BB:.*]], label %[[LOOP]]

; CHECK: [[BARRIER]]:
; CHECK: [[SUCCESS:%.*]] = phi i1 [ true, %[[TRY_STORE]] ], [ false, %[[LOOP]] ]
; CHECK: [[SUCCESS_BB]]:
; CHECK: fence acquire
; CHECK: br label %[[DONE:.*]]

; CHECK: [[FAILURE_BB]]:
; CHECK: fence acquire
; CHECK: br label %[[DONE]]

; CHECK: [[DONE]]:
; CHECK: [[SUCCESS:%.*]] = phi i1 [ true, %[[SUCCESS_BB]] ], [ false, %[[FAILURE_BB]] ]
; CHECK: ret i32 [[OLDVAL]]

%pairold = cmpxchg i32* %ptr, i32 %desired, i32 %newval acquire acquire
Expand All @@ -323,7 +335,7 @@ define i64 @test_cmpxchg_i64_monotonic_monotonic(i64* %ptr, i64 %desired, i64 %n
; CHECK: [[HI64:%.*]] = shl i64 [[HI64_TMP]], 32
; CHECK: [[OLDVAL:%.*]] = or i64 [[LO64]], [[HI64]]
; CHECK: [[SHOULD_STORE:%.*]] = icmp eq i64 [[OLDVAL]], %desired
; CHECK: br i1 [[SHOULD_STORE]], label %[[TRY_STORE:.*]], label %[[DONE:.*]]
; CHECK: br i1 [[SHOULD_STORE]], label %[[TRY_STORE:.*]], label %[[FAILURE_BB:.*]]

; CHECK: [[TRY_STORE]]:
; CHECK: [[NEWLO:%.*]] = trunc i64 %newval to i32
Expand All @@ -332,14 +344,18 @@ define i64 @test_cmpxchg_i64_monotonic_monotonic(i64* %ptr, i64 %desired, i64 %n
; CHECK: [[PTR8:%.*]] = bitcast i64* %ptr to i8*
; CHECK: [[TRYAGAIN:%.*]] = call i32 @llvm.arm.strexd(i32 [[NEWLO]], i32 [[NEWHI]], i8* [[PTR8]])
; CHECK: [[TST:%.*]] = icmp eq i32 [[TRYAGAIN]], 0
; CHECK: br i1 [[TST]], label %[[BARRIER:.*]], label %[[LOOP]]
; CHECK: br i1 [[TST]], label %[[SUCCESS_BB:.*]], label %[[LOOP]]

; CHECK: [[BARRIER]]:
; CHECK: [[SUCCESS_BB]]:
; CHECK-NOT: fence
; CHECK: br label %[[DONE:.*]]

; CHECK: [[FAILURE_BB]]:
; CHECK-NOT: fence
; CHECK: br label %[[DONE]]

; CHECK: [[DONE]]:
; CHECK: [[SUCCESS:%.*]] = phi i1 [ true, %[[BARRIER]] ], [ false, %[[LOOP]] ]
; CHECK: [[SUCCESS:%.*]] = phi i1 [ true, %[[SUCCESS_BB]] ], [ false, %[[FAILURE_BB]] ]
; CHECK: ret i64 [[OLDVAL]]

%pairold = cmpxchg i64* %ptr, i64 %desired, i64 %newval monotonic monotonic
Expand Down
53 changes: 35 additions & 18 deletions test/Transforms/AtomicExpandLoadLinked/ARM/atomic-expansion-v8.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -91,20 +91,24 @@ define i8 @test_cmpxchg_i8_seqcst_seqcst(i8* %ptr, i8 %desired, i8 %newval) {
; CHECK: [[OLDVAL32:%.*]] = call i32 @llvm.arm.ldaex.p0i8(i8* %ptr)
; CHECK: [[OLDVAL:%.*]] = trunc i32 %1 to i8
; CHECK: [[SHOULD_STORE:%.*]] = icmp eq i8 [[OLDVAL]], %desired
; CHECK: br i1 [[SHOULD_STORE]], label %[[TRY_STORE:.*]], label %[[BARRIER:.*]]
; CHECK: br i1 [[SHOULD_STORE]], label %[[TRY_STORE:.*]], label %[[FAILURE_BB:.*]]

; CHECK: [[TRY_STORE]]:
; CHECK: [[NEWVAL32:%.*]] = zext i8 %newval to i32
; CHECK: [[TRYAGAIN:%.*]] = call i32 @llvm.arm.stlex.p0i8(i32 [[NEWVAL32]], i8* %ptr)
; CHECK: [[TST:%.*]] = icmp eq i32 [[TRYAGAIN]], 0
; CHECK: br i1 [[TST]], label %[[BARRIER:.*]], label %[[LOOP]]
; CHECK: br i1 [[TST]], label %[[SUCCESS_BB:.*]], label %[[LOOP]]

; CHECK: [[BARRIER]]:
; CHECK: [[SUCCESS:%.*]] = phi i1 [ true, %[[TRY_STORE]] ], [ false, %[[LOOP]] ]
; CHECK-NOT: fence
; CHECK: [[SUCCESS_BB]]:
; CHECK-NOT: fence_cst
; CHECK: br label %[[DONE:.*]]

; CHECK: [[FAILURE_BB]]:
; CHECK-NOT: fence_cst
; CHECK: br label %[[DONE]]

; CHECK: [[DONE]]:
; CHECK: [[SUCCESS:%.*]] = phi i1 [ true, %[[SUCCESS_BB]] ], [ false, %[[FAILURE_BB]] ]
; CHECK: ret i8 [[OLDVAL]]

%pairold = cmpxchg i8* %ptr, i8 %desired, i8 %newval seq_cst seq_cst
Expand All @@ -121,20 +125,24 @@ define i16 @test_cmpxchg_i16_seqcst_monotonic(i16* %ptr, i16 %desired, i16 %newv
; CHECK: [[OLDVAL32:%.*]] = call i32 @llvm.arm.ldaex.p0i16(i16* %ptr)
; CHECK: [[OLDVAL:%.*]] = trunc i32 %1 to i16
; CHECK: [[SHOULD_STORE:%.*]] = icmp eq i16 [[OLDVAL]], %desired
; CHECK: br i1 [[SHOULD_STORE]], label %[[TRY_STORE:.*]], label %[[DONE:.*]]
; CHECK: br i1 [[SHOULD_STORE]], label %[[TRY_STORE:.*]], label %[[FAILURE_BB:.*]]

; CHECK: [[TRY_STORE]]:
; CHECK: [[NEWVAL32:%.*]] = zext i16 %newval to i32
; CHECK: [[TRYAGAIN:%.*]] = call i32 @llvm.arm.stlex.p0i16(i32 [[NEWVAL32]], i16* %ptr)
; CHECK: [[TST:%.*]] = icmp eq i32 [[TRYAGAIN]], 0
; CHECK: br i1 [[TST]], label %[[BARRIER:.*]], label %[[LOOP]]
; CHECK: br i1 [[TST]], label %[[SUCCESS_BB:.*]], label %[[LOOP]]

; CHECK: [[BARRIER]]:
; CHECK: [[SUCCESS_BB]]:
; CHECK-NOT: fence
; CHECK: br label %[[DONE:.*]]

; CHECK: [[FAILURE_BB]]:
; CHECK-NOT: fence
; CHECK: br label %[[DONE]]

; CHECK: [[DONE]]:
; CHECK: [[SUCCESS:%.*]] = phi i1 [ true, %[[BARRIER]] ], [ false, %[[LOOP]] ]
; CHECK: [[SUCCESS:%.*]] = phi i1 [ true, %[[SUCCESS_BB]] ], [ false, %[[FAILURE_BB]] ]
; CHECK: ret i16 [[OLDVAL]]

%pairold = cmpxchg i16* %ptr, i16 %desired, i16 %newval seq_cst monotonic
Expand All @@ -150,19 +158,23 @@ define i32 @test_cmpxchg_i32_acquire_acquire(i32* %ptr, i32 %desired, i32 %newva
; CHECK: [[LOOP]]:
; CHECK: [[OLDVAL:%.*]] = call i32 @llvm.arm.ldaex.p0i32(i32* %ptr)
; CHECK: [[SHOULD_STORE:%.*]] = icmp eq i32 [[OLDVAL]], %desired
; CHECK: br i1 [[SHOULD_STORE]], label %[[TRY_STORE:.*]], label %[[DONE:.*]]
; CHECK: br i1 [[SHOULD_STORE]], label %[[TRY_STORE:.*]], label %[[FAILURE_BB:.*]]

; CHECK: [[TRY_STORE]]:
; CHECK: [[TRYAGAIN:%.*]] = call i32 @llvm.arm.strex.p0i32(i32 %newval, i32* %ptr)
; CHECK: [[TST:%.*]] = icmp eq i32 [[TRYAGAIN]], 0
; CHECK: br i1 [[TST]], label %[[BARRIER:.*]], label %[[LOOP]]
; CHECK: br i1 [[TST]], label %[[SUCCESS_BB:.*]], label %[[LOOP]]

; CHECK: [[BARRIER]]:
; CHECK: [[SUCCESS:%.*]] = phi i1 [ true, %[[TRY_STORE]] ], [ false, %[[LOOP]] ]
; CHECK-NOT: fence
; CHECK: [[SUCCESS_BB]]:
; CHECK-NOT: fence_cst
; CHECK: br label %[[DONE:.*]]

; CHECK: [[FAILURE_BB]]:
; CHECK-NOT: fence_cst
; CHECK: br label %[[DONE]]

; CHECK: [[DONE]]:
; CHECK: [[SUCCESS:%.*]] = phi i1 [ true, %[[SUCCESS_BB]] ], [ false, %[[FAILURE_BB]] ]
; CHECK: ret i32 [[OLDVAL]]

%pairold = cmpxchg i32* %ptr, i32 %desired, i32 %newval acquire acquire
Expand All @@ -185,7 +197,7 @@ define i64 @test_cmpxchg_i64_monotonic_monotonic(i64* %ptr, i64 %desired, i64 %n
; CHECK: [[HI64:%.*]] = shl i64 [[HI64_TMP]], 32
; CHECK: [[OLDVAL:%.*]] = or i64 [[LO64]], [[HI64]]
; CHECK: [[SHOULD_STORE:%.*]] = icmp eq i64 [[OLDVAL]], %desired
; CHECK: br i1 [[SHOULD_STORE]], label %[[TRY_STORE:.*]], label %[[DONE:.*]]
; CHECK: br i1 [[SHOULD_STORE]], label %[[TRY_STORE:.*]], label %[[FAILURE_BB:.*]]

; CHECK: [[TRY_STORE]]:
; CHECK: [[NEWLO:%.*]] = trunc i64 %newval to i32
Expand All @@ -194,13 +206,18 @@ define i64 @test_cmpxchg_i64_monotonic_monotonic(i64* %ptr, i64 %desired, i64 %n
; CHECK: [[PTR8:%.*]] = bitcast i64* %ptr to i8*
; CHECK: [[TRYAGAIN:%.*]] = call i32 @llvm.arm.strexd(i32 [[NEWLO]], i32 [[NEWHI]], i8* [[PTR8]])
; CHECK: [[TST:%.*]] = icmp eq i32 [[TRYAGAIN]], 0
; CHECK: br i1 [[TST]], label %[[BARRIER:.*]], label %[[LOOP]]
; CHECK: br i1 [[TST]], label %[[SUCCESS_BB:.*]], label %[[LOOP]]

; CHECK: [[BARRIER]]:
; CHECK-NOT: fence
; CHECK: [[SUCCESS_BB]]:
; CHECK-NOT: fence_cst
; CHECK: br label %[[DONE:.*]]

; CHECK: [[FAILURE_BB]]:
; CHECK-NOT: fence_cst
; CHECK: br label %[[DONE]]

; CHECK: [[DONE]]:
; CHECK: [[SUCCESS:%.*]] = phi i1 [ true, %[[SUCCESS_BB]] ], [ false, %[[FAILURE_BB]] ]
; CHECK: ret i64 [[OLDVAL]]

%pairold = cmpxchg i64* %ptr, i64 %desired, i64 %newval monotonic monotonic
Expand Down
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