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When performing a conditional branch depending on the value of a comparison

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%cmp (eg: A==B) we already replace %cmp with "true" under the true edge, and
with "false" under the false edge.  This change enhances this to replace the
negated compare (A!=B) with "false" under the true edge and "true" under the
false edge.  Reported to improve perlbench results by 1%.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@151517 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan Sands 2012-02-27 08:14:30 +00:00
parent a89cc7fec8
commit 669011f50b
2 changed files with 126 additions and 4 deletions
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66
lib/Transforms/Scalar/GVN.cpp
View File

@ -96,12 +96,17 @@ namespace {
uint32_t nextValueNumber;
Expression create_expression(Instruction* I);
Expression create_cmp_expression(unsigned Opcode,
CmpInst::Predicate Predicate,
Value *LHS, Value *RHS);
Expression create_extractvalue_expression(ExtractValueInst* EI);
uint32_t lookup_or_add_call(CallInst* C);
public:
ValueTable() : nextValueNumber(1) { }
uint32_t lookup_or_add(Value *V);
uint32_t lookup(Value *V) const;
uint32_t lookup_or_add_cmp(unsigned Opcode, CmpInst::Predicate Pred,
Value *LHS, Value *RHS);
void add(Value *V, uint32_t num);
void clear();
void erase(Value *v);
@ -181,6 +186,25 @@ Expression ValueTable::create_expression(Instruction *I) {
return e;
}
Expression ValueTable::create_cmp_expression(unsigned Opcode,
CmpInst::Predicate Predicate,
Value *LHS, Value *RHS) {
assert((Opcode == Instruction::ICmp || Opcode == Instruction::FCmp) &&
"Not a comparison!");
Expression e;
e.type = CmpInst::makeCmpResultType(LHS->getType());
e.varargs.push_back(lookup_or_add(LHS));
e.varargs.push_back(lookup_or_add(RHS));
// Sort the operand value numbers so x<y and y>x get the same value number.
if (e.varargs[0] > e.varargs[1]) {
std::swap(e.varargs[0], e.varargs[1]);
Predicate = CmpInst::getSwappedPredicate(Predicate);
}
e.opcode = (Opcode << 8) | Predicate;
return e;
}
Expression ValueTable::create_extractvalue_expression(ExtractValueInst *EI) {
assert(EI != 0 && "Not an ExtractValueInst?");
Expression e;
@ -430,6 +454,19 @@ uint32_t ValueTable::lookup(Value *V) const {
return VI->second;
}
/// lookup_or_add_cmp - Returns the value number of the given comparison,
/// assigning it a new number if it did not have one before. Useful when
/// we deduced the result of a comparison, but don't immediately have an
/// instruction realizing that comparison to hand.
uint32_t ValueTable::lookup_or_add_cmp(unsigned Opcode,
CmpInst::Predicate Predicate,
Value *LHS, Value *RHS) {
Expression exp = create_cmp_expression(Opcode, Predicate, LHS, RHS);
uint32_t& e = expressionNumbering[exp];
if (!e) e = nextValueNumber++;
return e;
}
/// clear - Remove all entries from the ValueTable.
void ValueTable::clear() {
valueNumbering.clear();
@ -1987,14 +2024,35 @@ bool GVN::propagateEquality(Value *LHS, Value *RHS, BasicBlock *Root) {
}
// If we are propagating an equality like "(A == B)" == "true" then also
// propagate the equality A == B.
// 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)) {
// Only equality comparisons are supported.
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)) {
Value *Op0 = Cmp->getOperand(0), *Op1 = Cmp->getOperand(1);
(isKnownFalse && Cmp->getPredicate() == CmpInst::ICMP_NE))
Changed |= propagateEquality(Op0, Op1, Root);
// 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).
unsigned Num = VN.lookup_or_add_cmp(Cmp->getOpcode(), NotPred, Op0, Op1);
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);
return Changed;
}

64
test/Transforms/GVN/condprop.ll
View File

@ -111,3 +111,67 @@ case3:
; CHECK: call void @bar(i32 %x)
ret void
}
; CHECK: @test5
define i1 @test5(i32 %x, i32 %y) {
%cmp = icmp eq i32 %x, %y
br i1 %cmp, label %same, label %different
same:
%cmp2 = icmp ne i32 %x, %y
; CHECK: ret i1 false
ret i1 %cmp2
different:
%cmp3 = icmp eq i32 %x, %y
; CHECK: ret i1 false
ret i1 %cmp3
}
; CHECK: @test6
define i1 @test6(i32 %x, i32 %y) {
%cmp2 = icmp ne i32 %x, %y
%cmp = icmp eq i32 %x, %y
%cmp3 = icmp eq i32 %x, %y
br i1 %cmp, label %same, label %different
same:
; CHECK: ret i1 false
ret i1 %cmp2
different:
; CHECK: ret i1 false
ret i1 %cmp3
}
; CHECK: @test7
define i1 @test7(i32 %x, i32 %y) {
%cmp = icmp sgt i32 %x, %y
br i1 %cmp, label %same, label %different
same:
%cmp2 = icmp sle i32 %x, %y
; CHECK: ret i1 false
ret i1 %cmp2
different:
%cmp3 = icmp sgt i32 %x, %y
; CHECK: ret i1 false
ret i1 %cmp3
}
; CHECK: @test8
define i1 @test8(i32 %x, i32 %y) {
%cmp2 = icmp sle i32 %x, %y
%cmp = icmp sgt i32 %x, %y
%cmp3 = icmp sgt i32 %x, %y
br i1 %cmp, label %same, label %different
same:
; CHECK: ret i1 false
ret i1 %cmp2
different:
; CHECK: ret i1 false
ret i1 %cmp3
}