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Weak relaxing of the constraints on atomics in MemoryDependencyAnalysis

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Monotonic accesses do not have to kill the analysis, as long as the QueryInstr is not
itself atomic.

llvm-svn: 215942
This commit is contained in:
Robin Morisset 2014-08-18 22:18:11 +00:00
parent a9a28a5f89
commit f6230dcf49
2 changed files with 69 additions and 4 deletions
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26
lib/Analysis/MemoryDependenceAnalysis.cpp
View File

@ -409,9 +409,18 @@ getPointerDependencyFrom(const AliasAnalysis::Location &MemLoc, bool isLoad,
// a load depends on another must aliased load from the same value.
if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
// Atomic loads have complications involved.
// A monotonic load is OK if the query inst is itself not atomic.
// FIXME: This is overly conservative.
if (!LI->isUnordered())
return MemDepResult::getClobber(LI);
if (!LI->isUnordered()) {
if (!QueryInst || LI->getOrdering() != Monotonic)
return MemDepResult::getClobber(LI);
if (auto *QueryLI = dyn_cast<LoadInst>(QueryInst))
if (!QueryLI->isUnordered())
return MemDepResult::getClobber(LI);
if (auto *QuerySI = dyn_cast<StoreInst>(QueryInst))
if (!QuerySI->isUnordered())
return MemDepResult::getClobber(LI);
}
AliasAnalysis::Location LoadLoc = AA->getLocation(LI);
@ -469,9 +478,18 @@ getPointerDependencyFrom(const AliasAnalysis::Location &MemLoc, bool isLoad,
if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
// Atomic stores have complications involved.
// A monotonic store is OK if the query inst is itself not atomic.
// FIXME: This is overly conservative.
if (!SI->isUnordered())
return MemDepResult::getClobber(SI);
if (!SI->isUnordered()) {
if (!QueryInst || SI->getOrdering() != Monotonic)
return MemDepResult::getClobber(SI);
if (auto *QueryLI = dyn_cast<LoadInst>(QueryInst))
if (!QueryLI->isUnordered())
return MemDepResult::getClobber(SI);
if (auto *QuerySI = dyn_cast<StoreInst>(QueryInst))
if (!QuerySI->isUnordered())
return MemDepResult::getClobber(SI);
}
// If alias analysis can tell that this store is guaranteed to not modify
// the query pointer, ignore it. Use getModRefInfo to handle cases where

47
test/Transforms/DeadStoreElimination/atomic.ll
View File

@ -105,3 +105,50 @@ entry:
ret i32 %x
}
; DSE across monotonic load (allowed as long as the eliminated store isUnordered)
define i32 @test9() nounwind uwtable ssp {
; CHECK: test9
; CHECK-NOT: store i32 0
; CHECK: store i32 1
entry:
store i32 0, i32* @x
%x = load atomic i32* @y monotonic, align 4
store i32 1, i32* @x
ret i32 %x
}
; DSE across monotonic store (allowed as long as the eliminated store isUnordered)
define void @test10() nounwind uwtable ssp {
; CHECK: test10
; CHECK-NOT: store i32 0
; CHECK: store i32 1
entry:
store i32 0, i32* @x
store atomic i32 42, i32* @y monotonic, align 4
store i32 1, i32* @x
ret void
}
; DSE across monotonic load (forbidden since the eliminated store is atomic)
define i32 @test11() nounwind uwtable ssp {
; CHECK: test11
; CHECK: store atomic i32 0
; CHECK: store atomic i32 1
entry:
store atomic i32 0, i32* @x monotonic, align 4
%x = load atomic i32* @y monotonic, align 4
store atomic i32 1, i32* @x monotonic, align 4
ret i32 %x
}
; DSE across monotonic store (forbidden since the eliminated store is atomic)
define void @test12() nounwind uwtable ssp {
; CHECK: test12
; CHECK: store atomic i32 0
; CHECK: store atomic i32 1
entry:
store atomic i32 0, i32* @x monotonic, align 4
store atomic i32 42, i32* @y monotonic, align 4
store atomic i32 1, i32* @x monotonic, align 4
ret void
}