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Make GVN's propagateEquality non-recursive. No intended functionality change.

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The modifications are a lot more trivial than they appear to be in the diff!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@154174 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan Sands 2012-04-06 15:31:09 +00:00
parent f85cb768fe
commit a28bd85aa9
1 changed files with 104 additions and 97 deletions
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201
lib/Transforms/Scalar/GVN.cpp
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@ -1974,112 +1974,119 @@ unsigned GVN::replaceAllDominatedUsesWith(Value *From, Value *To,
/// dominated by 'Root'. Exploit this, for example by replacing 'LHS' with
/// 'RHS' everywhere in the scope. Returns whether a change was made.
bool GVN::propagateEquality(Value *LHS, Value *RHS, BasicBlock *Root) {
if (LHS == RHS) return false;
assert(LHS->getType() == RHS->getType() && "Equal but types differ!");
// Don't try to propagate equalities between constants.
if (isa<Constant>(LHS) && isa<Constant>(RHS))
return false;
// Prefer a constant on the right-hand side, or an Argument if no constants.
if (isa<Constant>(LHS) || (isa<Argument>(LHS) && !isa<Constant>(RHS)))
std::swap(LHS, RHS);
assert((isa<Argument>(LHS) || isa<Instruction>(LHS)) && "Unexpected value!");
// If there is no obvious reason to prefer the left-hand side over the right-
// hand side, ensure the longest lived term is on the right-hand side, so the
// shortest lived term will be replaced by the longest lived. This tends to
// expose more simplifications.
uint32_t LVN = VN.lookup_or_add(LHS);
if ((isa<Argument>(LHS) && isa<Argument>(RHS)) ||
(isa<Instruction>(LHS) && isa<Instruction>(RHS))) {
// Move the 'oldest' value to the right-hand side, using the value number as
// a proxy for age.
uint32_t RVN = VN.lookup_or_add(RHS);
if (LVN < RVN) {
std::swap(LHS, RHS);
LVN = RVN;
}
}
assert((!isa<Instruction>(RHS) ||
DT->properlyDominates(cast<Instruction>(RHS)->getParent(), Root)) &&
"Instruction doesn't dominate scope!");
// If value numbering later deduces that an instruction in the scope is equal
// to 'LHS' then ensure it will be turned into 'RHS'.
addToLeaderTable(LVN, RHS, Root);
// Replace all occurrences of 'LHS' with 'RHS' everywhere in the scope. As
// LHS always has at least one use that is not dominated by Root, this will
// never do anything if LHS has only one use.
SmallVector<std::pair<Value*, Value*>, 4> Worklist;
Worklist.push_back(std::make_pair(LHS, RHS));
bool Changed = false;
if (!LHS->hasOneUse()) {
unsigned NumReplacements = replaceAllDominatedUsesWith(LHS, RHS, Root);
Changed |= NumReplacements > 0;
NumGVNEqProp += NumReplacements;
}
// Now try to deduce additional equalities from this one. For example, if the
// known equality was "(A != B)" == "false" then it follows that A and B are
// equal in the scope. Only boolean equalities with an explicit true or false
// RHS are currently supported.
if (!RHS->getType()->isIntegerTy(1))
// Not a boolean equality - bail out.
return Changed;
ConstantInt *CI = dyn_cast<ConstantInt>(RHS);
if (!CI)
// RHS neither 'true' nor 'false' - bail out.
return Changed;
// Whether RHS equals 'true'. Otherwise it equals 'false'.
bool isKnownTrue = CI->isAllOnesValue();
bool isKnownFalse = !isKnownTrue;
while (!Worklist.empty()) {
std::pair<Value*, Value*> Item = Worklist.pop_back_val();
LHS = Item.first; RHS = Item.second;
// If "A && B" is known true then both A and B are known true. If "A || B"
// is known false then both A and B are known false.
Value *A, *B;
if ((isKnownTrue && match(LHS, m_And(m_Value(A), m_Value(B)))) ||
(isKnownFalse && match(LHS, m_Or(m_Value(A), m_Value(B))))) {
Changed |= propagateEquality(A, RHS, Root);
Changed |= propagateEquality(B, RHS, Root);
return Changed;
}
if (LHS == RHS) continue;
assert(LHS->getType() == RHS->getType() && "Equality but unequal types!");
// If we are propagating an equality like "(A == B)" == "true" then also
// propagate the equality A == B. When propagating a comparison such as
// "(A >= B)" == "true", replace all instances of "A < B" with "false".
if (ICmpInst *Cmp = dyn_cast<ICmpInst>(LHS)) {
Value *Op0 = Cmp->getOperand(0), *Op1 = Cmp->getOperand(1);
// Don't try to propagate equalities between constants.
if (isa<Constant>(LHS) && isa<Constant>(RHS)) continue;
// If "A == B" is known true, or "A != B" is known false, then replace
// A with B everywhere in the scope.
if ((isKnownTrue && Cmp->getPredicate() == CmpInst::ICMP_EQ) ||
(isKnownFalse && Cmp->getPredicate() == CmpInst::ICMP_NE))
Changed |= propagateEquality(Op0, Op1, Root);
// Prefer a constant on the right-hand side, or an Argument if no constants.
if (isa<Constant>(LHS) || (isa<Argument>(LHS) && !isa<Constant>(RHS)))
std::swap(LHS, RHS);
assert((isa<Argument>(LHS) || isa<Instruction>(LHS)) && "Unexpected value!");
// If "A >= B" is known true, replace "A < B" with false everywhere.
CmpInst::Predicate NotPred = Cmp->getInversePredicate();
Constant *NotVal = ConstantInt::get(Cmp->getType(), isKnownFalse);
// Since we don't have the instruction "A < B" immediately to hand, work out
// the value number that it would have and use that to find an appropriate
// instruction (if any).
uint32_t NextNum = VN.getNextUnusedValueNumber();
uint32_t Num = VN.lookup_or_add_cmp(Cmp->getOpcode(), NotPred, Op0, Op1);
// If the number we were assigned was brand new then there is no point in
// looking for an instruction realizing it: there cannot be one!
if (Num < NextNum) {
Value *NotCmp = findLeader(Root, Num);
if (NotCmp && isa<Instruction>(NotCmp)) {
unsigned NumReplacements =
replaceAllDominatedUsesWith(NotCmp, NotVal, Root);
Changed |= NumReplacements > 0;
NumGVNEqProp += NumReplacements;
// If there is no obvious reason to prefer the left-hand side over the right-
// hand side, ensure the longest lived term is on the right-hand side, so the
// shortest lived term will be replaced by the longest lived. This tends to
// expose more simplifications.
uint32_t LVN = VN.lookup_or_add(LHS);
if ((isa<Argument>(LHS) && isa<Argument>(RHS)) ||
(isa<Instruction>(LHS) && isa<Instruction>(RHS))) {
// Move the 'oldest' value to the right-hand side, using the value number as
// a proxy for age.
uint32_t RVN = VN.lookup_or_add(RHS);
if (LVN < RVN) {
std::swap(LHS, RHS);
LVN = RVN;
}
}
// Ensure that any instruction in scope that gets the "A < B" value number
// is replaced with false.
addToLeaderTable(Num, NotVal, Root);
assert((!isa<Instruction>(RHS) ||
DT->properlyDominates(cast<Instruction>(RHS)->getParent(), Root)) &&
"Instruction doesn't dominate scope!");
return Changed;
// If value numbering later deduces that an instruction in the scope is equal
// to 'LHS' then ensure it will be turned into 'RHS'.
addToLeaderTable(LVN, RHS, Root);
// Replace all occurrences of 'LHS' with 'RHS' everywhere in the scope. As
// LHS always has at least one use that is not dominated by Root, this will
// never do anything if LHS has only one use.
if (!LHS->hasOneUse()) {
unsigned NumReplacements = replaceAllDominatedUsesWith(LHS, RHS, Root);
Changed |= NumReplacements > 0;
NumGVNEqProp += NumReplacements;
}
// Now try to deduce additional equalities from this one. For example, if the
// known equality was "(A != B)" == "false" then it follows that A and B are
// equal in the scope. Only boolean equalities with an explicit true or false
// RHS are currently supported.
if (!RHS->getType()->isIntegerTy(1))
// Not a boolean equality - bail out.
continue;
ConstantInt *CI = dyn_cast<ConstantInt>(RHS);
if (!CI)
// RHS neither 'true' nor 'false' - bail out.
continue;
// Whether RHS equals 'true'. Otherwise it equals 'false'.
bool isKnownTrue = CI->isAllOnesValue();
bool isKnownFalse = !isKnownTrue;
// If "A && B" is known true then both A and B are known true. If "A || B"
// is known false then both A and B are known false.
Value *A, *B;
if ((isKnownTrue && match(LHS, m_And(m_Value(A), m_Value(B)))) ||
(isKnownFalse && match(LHS, m_Or(m_Value(A), m_Value(B))))) {
Worklist.push_back(std::make_pair(A, RHS));
Worklist.push_back(std::make_pair(B, RHS));
continue;
}
// If we are propagating an equality like "(A == B)" == "true" then also
// propagate the equality A == B. When propagating a comparison such as
// "(A >= B)" == "true", replace all instances of "A < B" with "false".
if (ICmpInst *Cmp = dyn_cast<ICmpInst>(LHS)) {
Value *Op0 = Cmp->getOperand(0), *Op1 = Cmp->getOperand(1);
// If "A == B" is known true, or "A != B" is known false, then replace
// A with B everywhere in the scope.
if ((isKnownTrue && Cmp->getPredicate() == CmpInst::ICMP_EQ) ||
(isKnownFalse && Cmp->getPredicate() == CmpInst::ICMP_NE))
Worklist.push_back(std::make_pair(Op0, Op1));
// If "A >= B" is known true, replace "A < B" with false everywhere.
CmpInst::Predicate NotPred = Cmp->getInversePredicate();
Constant *NotVal = ConstantInt::get(Cmp->getType(), isKnownFalse);
// Since we don't have the instruction "A < B" immediately to hand, work out
// the value number that it would have and use that to find an appropriate
// instruction (if any).
uint32_t NextNum = VN.getNextUnusedValueNumber();
uint32_t Num = VN.lookup_or_add_cmp(Cmp->getOpcode(), NotPred, Op0, Op1);
// If the number we were assigned was brand new then there is no point in
// looking for an instruction realizing it: there cannot be one!
if (Num < NextNum) {
Value *NotCmp = findLeader(Root, Num);
if (NotCmp && isa<Instruction>(NotCmp)) {
unsigned NumReplacements =
replaceAllDominatedUsesWith(NotCmp, NotVal, Root);
Changed |= NumReplacements > 0;
NumGVNEqProp += NumReplacements;
}
}
// Ensure that any instruction in scope that gets the "A < B" value number
// is replaced with false.
addToLeaderTable(Num, NotVal, Root);
continue;
}
}
return Changed;