6502/llvm-6502
1
0
Fork 0
mirror of https://github.com/c64scene-ar/llvm-6502.git synced 2025-03-04 05:31:51 +00:00
Code Issues Projects Releases Wiki Activity

Significantly improve the documentation of the instcombine divide/compare

Browse Source 
transformation.  Also, keep track of which end of the integer interval overflows
occur on.  This fixes Transforms/InstCombine/2007-06-21-DivCompareMiscomp.ll
and rdar://5278853, a miscompilation of perl.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@37692 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2007-06-21 18:11:19 +00:00
parent e47f30f5e6
commit 1dbfd48fa2
1 changed files with 50 additions and 34 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

84
lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -5131,12 +5131,7 @@ Instruction *InstCombiner::FoldICmpDivCst(ICmpInst &ICI, BinaryOperator *DivI,
if (!ICI.isEquality() && DivIsSigned != ICI.isSignedPredicate())
return 0;
if (DivRHS->isZero())
return 0; // Don't hack on div by zero
// Initialize the variables that will indicate the nature of the
// range check.
bool LoOverflow = false, HiOverflow = false;
ConstantInt *LoBound = 0, *HiBound = 0;
return 0; // The ProdOV computation fails on divide by zero.
// Compute Prod = CI * DivRHS. We are essentially solving an equation
// of form X/C1=C2. We solve for X by multiplying C1 (DivRHS) and
@ -5151,87 +5146,108 @@ Instruction *InstCombiner::FoldICmpDivCst(ICmpInst &ICI, BinaryOperator *DivI,
ConstantExpr::getUDiv(Prod, DivRHS)) != CmpRHS;
// Get the ICmp opcode
ICmpInst::Predicate predicate = ICI.getPredicate();
ICmpInst::Predicate Pred = ICI.getPredicate();
// Figure out the interval that is being checked. For example, a comparison
// like "X /u 5 == 0" is really checking that X is in the interval [0, 5).
// Compute this interval based on the constants involved and the signedness of
// the compare/divide. This computes a half-open interval, keeping track of
// whether either value in the interval overflows. After analysis each
// overflow variable is set to 0 if it's corresponding bound variable is valid
// -1 if overflowed off the bottom end, or +1 if overflowed off the top end.
int LoOverflow = 0, HiOverflow = 0;
ConstantInt *LoBound = 0, *HiBound = 0;
if (!DivIsSigned) { // udiv
// e.g. X/5 op 3 --> [15, 20)
LoBound = Prod;
LoOverflow = ProdOV;
HiOverflow = ProdOV || AddWithOverflow(HiBound, LoBound, DivRHS, false);
HiOverflow = LoOverflow = ProdOV;
if (!HiOverflow)
HiOverflow = AddWithOverflow(HiBound, LoBound, DivRHS, false);
} else if (DivRHS->getValue().isPositive()) { // Divisor is > 0.
if (CmpRHSV == 0) { // (X / pos) op 0
// Can't overflow.
// Can't overflow. e.g. X/2 op 0 --> [-1, 2)
LoBound = cast<ConstantInt>(ConstantExpr::getNeg(SubOne(DivRHS)));
HiBound = DivRHS;
} else if (CmpRHSV.isPositive()) { // (X / pos) op pos
LoBound = Prod;
LoOverflow = ProdOV;
HiOverflow = ProdOV || AddWithOverflow(HiBound, Prod, DivRHS, true);
LoBound = Prod; // e.g. X/5 op 3 --> [15, 20)
HiOverflow = LoOverflow = ProdOV;
if (!HiOverflow)
HiOverflow = AddWithOverflow(HiBound, Prod, DivRHS, true);
} else { // (X / pos) op neg
// e.g. X/5 op -3 --> [-15-4, -15+1) --> [-19, -14)
Constant *DivRHSH = ConstantExpr::getNeg(SubOne(DivRHS));
LoOverflow = AddWithOverflow(LoBound, Prod,
cast<ConstantInt>(DivRHSH), true);
cast<ConstantInt>(DivRHSH), true) ? -1 : 0;
HiBound = AddOne(Prod);
HiOverflow = ProdOV;
HiOverflow = ProdOV ? -1 : 0;
}
} else { // Divisor is < 0.
if (CmpRHSV == 0) { // (X / neg) op 0
// e.g. X/-5 op 0 --> [-4, 5)
LoBound = AddOne(DivRHS);
HiBound = cast<ConstantInt>(ConstantExpr::getNeg(DivRHS));
if (HiBound == DivRHS)
return 0; // - INTMIN = INTMIN
if (HiBound == DivRHS) { // -INTMIN = INTMIN
HiOverflow = 1; // [INTMIN+1, overflow)
HiBound = 0; // e.g. X/INTMIN = 0 --> X > INTMIN
}
} else if (CmpRHSV.isPositive()) { // (X / neg) op pos
HiOverflow = LoOverflow = ProdOV;
// e.g. X/-5 op 3 --> [-19, -14)
HiOverflow = LoOverflow = ProdOV ? -1 : 0;
if (!LoOverflow)
LoOverflow = AddWithOverflow(LoBound, Prod, AddOne(DivRHS),
true);
LoOverflow = AddWithOverflow(LoBound, Prod, AddOne(DivRHS), true) ?-1:0;
HiBound = AddOne(Prod);
} else { // (X / neg) op neg
// e.g. X/-5 op -3 --> [15, 20)
LoBound = Prod;
LoOverflow = HiOverflow = ProdOV;
LoOverflow = HiOverflow = ProdOV ? 1 : 0;
HiBound = Subtract(Prod, DivRHS);
}
// Dividing by a negate swaps the condition.
predicate = ICmpInst::getSwappedPredicate(predicate);
// Dividing by a negative swaps the condition. LT <-> GT
Pred = ICmpInst::getSwappedPredicate(Pred);
}
Value *X = DivI->getOperand(0);
switch (predicate) {
switch (Pred) {
default: assert(0 && "Unhandled icmp opcode!");
case ICmpInst::ICMP_EQ:
if (LoOverflow && HiOverflow)
return ReplaceInstUsesWith(ICI, ConstantInt::getFalse());
else if (HiOverflow)
return new ICmpInst(DivIsSigned ? ICmpInst::ICMP_SGE :
return new ICmpInst(DivIsSigned ? ICmpInst::ICMP_SGE :
ICmpInst::ICMP_UGE, X, LoBound);
else if (LoOverflow)
return new ICmpInst(DivIsSigned ? ICmpInst::ICMP_SLT :
ICmpInst::ICMP_ULT, X, HiBound);
else
return InsertRangeTest(X, LoBound, HiBound, DivIsSigned,
true, ICI);
return InsertRangeTest(X, LoBound, HiBound, DivIsSigned, true, ICI);
case ICmpInst::ICMP_NE:
if (LoOverflow && HiOverflow)
return ReplaceInstUsesWith(ICI, ConstantInt::getTrue());
else if (HiOverflow)
return new ICmpInst(DivIsSigned ? ICmpInst::ICMP_SLT :
return new ICmpInst(DivIsSigned ? ICmpInst::ICMP_SLT :
ICmpInst::ICMP_ULT, X, LoBound);
else if (LoOverflow)
return new ICmpInst(DivIsSigned ? ICmpInst::ICMP_SGE :
ICmpInst::ICMP_UGE, X, HiBound);
else
return InsertRangeTest(X, LoBound, HiBound, DivIsSigned,
false, ICI);
return InsertRangeTest(X, LoBound, HiBound, DivIsSigned, false, ICI);
case ICmpInst::ICMP_ULT:
case ICmpInst::ICMP_SLT:
if (LoOverflow)
if (LoOverflow == +1) // Low bound is greater than input range.
return ReplaceInstUsesWith(ICI, ConstantInt::getTrue());
if (LoOverflow == -1) // Low bound is less than input range.
return ReplaceInstUsesWith(ICI, ConstantInt::getFalse());
return new ICmpInst(predicate, X, LoBound);
return new ICmpInst(Pred, X, LoBound);
case ICmpInst::ICMP_UGT:
case ICmpInst::ICMP_SGT:
if (HiOverflow)
if (HiOverflow == +1) // High bound greater than input range.
return ReplaceInstUsesWith(ICI, ConstantInt::getFalse());
if (predicate == ICmpInst::ICMP_UGT)
else if (HiOverflow == -1) // High bound less than input range.
return ReplaceInstUsesWith(ICI, ConstantInt::getTrue());
if (Pred == ICmpInst::ICMP_UGT)
return new ICmpInst(ICmpInst::ICMP_UGE, X, HiBound);
else
return new ICmpInst(ICmpInst::ICMP_SGE, X, HiBound);