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369e0e389f
DMB instructions can be expensive, so it's best to avoid them if possible. In
atomicrmw operations there will always be an attempted store so a release
barrier is always needed, but in the cmpxchg case we can delay the DMB until we
know we'll definitely try to perform a store (and so need release semantics).
In the strong cmpxchg case this isn't quite free: we must duplicate the LDREX
instructions to skip the barrier on subsequent iterations. The basic outline
becomes:
ldrex rOld, [rAddr]
cmp rOld, rDesired
bne Ldone
dmb
Lloop:
strex rRes, rNew, [rAddr]
cbz rRes Ldone
ldrex rOld, [rAddr]
cmp rOld, rDesired
beq Lloop
Ldone:
So we'll skip this version for strong operations in "minsize" functions.
llvm-svn: 261568
125 lines
2.9 KiB
LLVM
125 lines
2.9 KiB
LLVM
; RUN: llc -mtriple=thumbv7s-apple-ios7.0 -o - %s | FileCheck %s
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define i32 @test_return(i32* %p, i32 %oldval, i32 %newval) {
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; CHECK-LABEL: test_return:
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; CHECK: ldrex [[LOADED:r[0-9]+]], [r0]
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; CHECK: cmp [[LOADED]], r1
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; CHECK: bne [[FAILED:LBB[0-9]+_[0-9]+]]
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; CHECK: dmb ishst
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; CHECK: [[LOOP:LBB[0-9]+_[0-9]+]]:
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; CHECK: strex [[STATUS:r[0-9]+]], {{r[0-9]+}}, [r0]
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; CHECK: cbz [[STATUS]], [[SUCCESS:LBB[0-9]+_[0-9]+]]
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; CHECK: ldrex [[LOADED]], [r0]
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; CHECK: cmp [[LOADED]], r1
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; CHECK: beq [[LOOP]]
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; CHECK: [[FAILED]]:
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; CHECK-NOT: cmp {{r[0-9]+}}, {{r[0-9]+}}
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; CHECK: clrex
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; CHECK: dmb ish
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; CHECK: movs r0, #0
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; CHECK: bx lr
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; CHECK: [[SUCCESS]]:
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; CHECK-NOT: cmp {{r[0-9]+}}, {{r[0-9]+}}
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; CHECK: dmb ish
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; CHECK: movs r0, #1
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; CHECK: bx lr
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%pair = cmpxchg i32* %p, i32 %oldval, i32 %newval seq_cst seq_cst
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%success = extractvalue { i32, i1 } %pair, 1
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%conv = zext i1 %success to i32
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ret i32 %conv
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}
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define i1 @test_return_bool(i8* %value, i8 %oldValue, i8 %newValue) {
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; CHECK-LABEL: test_return_bool:
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; CHECK: uxtb [[OLDBYTE:r[0-9]+]], r1
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; CHECK: ldrexb [[LOADED:r[0-9]+]], [r0]
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; CHECK: cmp [[LOADED]], [[OLDBYTE]]
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; CHECK: bne [[FAIL:LBB[0-9]+_[0-9]+]]
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; CHECK: dmb ishst
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; CHECK: [[LOOP:LBB[0-9]+_[0-9]+]]:
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; CHECK: strexb [[STATUS:r[0-9]+]], {{r[0-9]+}}, [r0]
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; CHECK: cbz [[STATUS]], [[SUCCESS:LBB[0-9]+_[0-9]+]]
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; CHECK: ldrexb [[LOADED]], [r0]
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; CHECK: cmp [[LOADED]], [[OLDBYTE]]
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; CHECK: beq [[LOOP]]
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; FIXME: this eor is redundant. Need to teach DAG combine that.
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; CHECK: [[FAIL]]:
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; CHECK: clrex
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; CHECK: movs [[TMP:r[0-9]+]], #0
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; CHECK: eor r0, [[TMP]], #1
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; CHECK: bx lr
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; CHECK: [[SUCCESS]]:
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; CHECK-NOT: cmp {{r[0-9]+}}, {{r[0-9]+}}
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; CHECK: movs [[TMP:r[0-9]+]], #1
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; CHECK: eor r0, [[TMP]], #1
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; CHECK: bx lr
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%pair = cmpxchg i8* %value, i8 %oldValue, i8 %newValue acq_rel monotonic
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%success = extractvalue { i8, i1 } %pair, 1
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%failure = xor i1 %success, 1
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ret i1 %failure
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}
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define void @test_conditional(i32* %p, i32 %oldval, i32 %newval) {
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; CHECK-LABEL: test_conditional:
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; CHECK: ldrex [[LOADED:r[0-9]+]], [r0]
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; CHECK: cmp [[LOADED]], r1
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; CHECK: bne [[FAILED:LBB[0-9]+_[0-9]+]]
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; CHECK: dmb ishst
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; CHECK: [[LOOP:LBB[0-9]+_[0-9]+]]:
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; CHECK: strex [[STATUS:r[0-9]+]], r2, [r0]
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; CHECK: cbz [[STATUS]], [[SUCCESS:LBB[0-9]+_[0-9]+]]
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; CHECK: ldrex [[LOADED]], [r0]
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; CHECK: cmp [[LOADED]], r1
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; CHECK: beq [[LOOP]]
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; CHECK: [[FAILED]]:
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; CHECK-NOT: cmp {{r[0-9]+}}, {{r[0-9]+}}
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; CHECK: clrex
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; CHECK: dmb ish
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; CHECK: b.w _baz
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; CHECK: [[SUCCESS]]:
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; CHECK-NOT: cmp {{r[0-9]+}}, {{r[0-9]+}}
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; CHECK: dmb ish
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; CHECK: b.w _bar
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%pair = cmpxchg i32* %p, i32 %oldval, i32 %newval seq_cst seq_cst
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%success = extractvalue { i32, i1 } %pair, 1
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br i1 %success, label %true, label %false
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true:
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tail call void @bar() #2
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br label %end
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false:
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tail call void @baz() #2
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br label %end
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end:
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ret void
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}
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declare void @bar()
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declare void @baz()
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