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Revert r282168 "GVN-hoist: fix store past load dependence analysis (PR30216)"

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and also the dependent r282175 "GVN-hoist: do not dereference null pointers"

It's causing compiler crashes building Harfbuzz (PR30499).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@282199 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Hans Wennborg 2016-09-22 21:20:53 +00:00
parent 319d69e0f2
commit 579bab4252
2 changed files with 29 additions and 88 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

65
lib/Transforms/Scalar/GVNHoist.cpp
View File

@ -329,56 +329,49 @@ private:
return I1DFS < I2DFS;
}
// Return true when there are memory uses of Def in BB.
bool hasMemoryUseOnPath(const Instruction *NewPt, MemoryDef *Def, const BasicBlock *BB) {
const Instruction *OldPt = Def->getMemoryInst();
// Return true when there are users of Def in BB.
bool hasMemoryUseOnPath(MemoryAccess *Def, const BasicBlock *BB,
const Instruction *OldPt) {
const BasicBlock *DefBB = Def->getBlock();
const BasicBlock *OldBB = OldPt->getParent();
const BasicBlock *NewBB = NewPt->getParent();
bool ReachedNewPt = false;
MemoryLocation DefLoc = MemoryLocation::get(OldPt);
const MemorySSA::AccessList *Acc = MSSA->getBlockAccesses(BB);
if (!Acc)
return false;
for (User *U : Def->users())
if (auto *MU = dyn_cast<MemoryUse>(U)) {
// FIXME: MU->getBlock() does not get updated when we move the instruction.
BasicBlock *UBB = MU->getMemoryInst()->getParent();
// Only analyze uses in BB.
if (BB != UBB)
continue;
for (const MemoryAccess &MA : *Acc) {
auto *MU = dyn_cast<MemoryUse>(&MA);
if (!MU)
continue;
// Do not check whether MU aliases Def when MU occurs after OldPt.
if (BB == OldBB && firstInBB(OldPt, MU->getMemoryInst()))
break;
// Do not check whether MU aliases Def when MU occurs before NewPt.
if (BB == NewBB) {
if (!ReachedNewPt) {
if (firstInBB(MU->getMemoryInst(), NewPt))
continue;
ReachedNewPt = true;
// A use in the same block as the Def is on the path.
if (UBB == DefBB) {
assert(MSSA->locallyDominates(Def, MU) && "def not dominating use");
return true;
}
}
if (!AA->isNoAlias(DefLoc, MemoryLocation::get(MU->getMemoryInst())))
return true;
}
if (UBB != OldBB)
return true;
// It is only harmful to hoist when the use is before OldPt.
if (firstInBB(MU->getMemoryInst(), OldPt))
return true;
}
return false;
}
// Return true when there are exception handling or loads of memory Def
// between Def and NewPt. This function is only called for stores: Def is
// the MemoryDef of the store to be hoisted.
// between OldPt and NewPt.
// Decrement by 1 NBBsOnAllPaths for each block between HoistPt and BB, and
// return true when the counter NBBsOnAllPaths reaces 0, except when it is
// initialized to -1 which is unlimited.
bool hasEHOrLoadsOnPath(const Instruction *NewPt, MemoryDef *Def,
int &NBBsOnAllPaths) {
bool hasEHOrLoadsOnPath(const Instruction *NewPt, const Instruction *OldPt,
MemoryAccess *Def, int &NBBsOnAllPaths) {
const BasicBlock *NewBB = NewPt->getParent();
const BasicBlock *OldBB = Def->getBlock();
const BasicBlock *OldBB = OldPt->getParent();
assert(DT->dominates(NewBB, OldBB) && "invalid path");
assert(DT->dominates(Def->getDefiningAccess()->getBlock(), NewBB) &&
assert(DT->dominates(Def->getBlock(), NewBB) &&
"def does not dominate new hoisting point");
// Walk all basic blocks reachable in depth-first iteration on the inverse
@ -397,7 +390,7 @@ private:
return true;
// Check that we do not move a store past loads.
if (hasMemoryUseOnPath(NewPt, Def, *I))
if (hasMemoryUseOnPath(Def, *I, OldPt))
return true;
// Stop walk once the limit is reached.
@ -480,7 +473,7 @@ private:
// Check for unsafe hoistings due to side effects.
if (K == InsKind::Store) {
if (hasEHOrLoadsOnPath(NewPt, dyn_cast<MemoryDef>(U), NBBsOnAllPaths))
if (hasEHOrLoadsOnPath(NewPt, OldPt, D, NBBsOnAllPaths))
return false;
} else if (hasEHOnPath(NewBB, OldBB, NBBsOnAllPaths))
return false;

52
test/Transforms/GVNHoist/pr30216.ll
View File

@ -1,52 +0,0 @@
; RUN: opt -S -gvn-hoist < %s | FileCheck %s
; Make sure the two stores @B do not get hoisted past the load @B.
; CHECK-LABEL: define i8* @Foo
; CHECK: store
; CHECK: store
; CHECK: load
; CHECK: store
@A = external global i8
@B = external global i8*
define i8* @Foo() {
store i8 0, i8* @A
br i1 undef, label %if.then, label %if.else
if.then:
store i8* null, i8** @B
ret i8* null
if.else:
%1 = load i8*, i8** @B
store i8* null, i8** @B
ret i8* %1
}
; Make sure the two stores @B do not get hoisted past the store @GlobalVar.
; CHECK-LABEL: define i8* @Fun
; CHECK: store
; CHECK: store
; CHECK: store
; CHECK: store
; CHECK: load
@GlobalVar = internal global i8 0
define i8* @Fun() {
store i8 0, i8* @A
br i1 undef, label %if.then, label %if.else
if.then:
store i8* null, i8** @B
ret i8* null
if.else:
store i8 0, i8* @GlobalVar
store i8* null, i8** @B
%1 = load i8*, i8** @B
ret i8* %1
}