diff options
Diffstat (limited to 'lib/Transforms')
| -rw-r--r-- | lib/Transforms/Scalar/InstructionCombining.cpp | 77 |
1 files changed, 74 insertions, 3 deletions
diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp index 4f4296f..07f7b26 100644 --- a/lib/Transforms/Scalar/InstructionCombining.cpp +++ b/lib/Transforms/Scalar/InstructionCombining.cpp @@ -257,7 +257,8 @@ namespace { ConstantInt *RHS); Instruction *FoldICmpDivCst(ICmpInst &ICI, BinaryOperator *DivI, ConstantInt *DivRHS); - + Instruction *FoldICmpAddOpCst(ICmpInst &ICI, Value *X, ConstantInt *CI, + ICmpInst::Predicate Pred); Instruction *FoldGEPICmp(GEPOperator *GEPLHS, Value *RHS, ICmpInst::Predicate Cond, Instruction &I); Instruction *FoldShiftByConstant(Value *Op0, ConstantInt *Op1, @@ -6600,9 +6601,80 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) { } } } + + { + Value *X; ConstantInt *Cst; + // icmp (X+Cst), X + if (match(Op0, m_Add(m_Value(X), m_ConstantInt(Cst))) && Op1 == X) + return FoldICmpAddOpCst(I, X, Cst, I.getPredicate()); + + // icmp X, X+Cst + if (match(Op1, m_Add(m_Value(X), m_ConstantInt(Cst))) && Op0 == X) + return FoldICmpAddOpCst(I, X, Cst, I.getSwappedPredicate()); + } return Changed ? &I : 0; } +/// FoldICmpAddOpCst - Fold "icmp pred (X+CI), X". +Instruction *InstCombiner::FoldICmpAddOpCst(ICmpInst &ICI, + Value *X, ConstantInt *CI, + ICmpInst::Predicate Pred) { + // If we have X+0, exit early (simplifying logic below) and let it get folded + // elsewhere. icmp X+0, X -> icmp X, X + if (CI->isZero()) { + bool isTrue = ICmpInst::isTrueWhenEqual(Pred); + return ReplaceInstUsesWith(ICI, ConstantInt::get(ICI.getType(), isTrue)); + } + + // (X+4) == X -> false. + if (Pred == ICmpInst::ICMP_EQ) + return ReplaceInstUsesWith(ICI, ConstantInt::getFalse(X->getContext())); + + // (X+4) != X -> true. + if (Pred == ICmpInst::ICMP_NE) + return ReplaceInstUsesWith(ICI, ConstantInt::getTrue(X->getContext())); + + // From this point on, we know that (X+C <= X) --> (X+C < X) because C != 0, + // so the values can never be equal. Similiarly for all other "or equals" + // operators. + + // (X+1) <u X --> X >u (MAXUINT-1) --> X != 255 + // (X+2) <u X --> X >u (MAXUINT-2) --> X > 253 + // (X+MAXUINT) <u X --> X >u (MAXUINT-MAXUINT) --> X != 0 + if (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_ULE) { + Value *R = ConstantExpr::getSub(ConstantInt::get(CI->getType(), -1ULL), CI); + return new ICmpInst(ICmpInst::ICMP_UGT, X, R); + } + + // (X+1) >u X --> X <u (0-1) --> X != 255 + // (X+2) >u X --> X <u (0-2) --> X <u 254 + // (X+MAXUINT) >u X --> X <u (0-MAXUINT) --> X <u 1 --> X == 0 + if (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_UGE) + return new ICmpInst(ICmpInst::ICMP_ULT, X, ConstantExpr::getNeg(CI)); + + unsigned BitWidth = CI->getType()->getPrimitiveSizeInBits(); + ConstantInt *SMax = ConstantInt::get(X->getContext(), + APInt::getSignedMaxValue(BitWidth)); + + // (X+ 1) <s X --> X >s (MAXSINT-1) --> X == 127 + // (X+ 2) <s X --> X >s (MAXSINT-2) --> X >s 125 + // (X+MAXSINT) <s X --> X >s (MAXSINT-MAXSINT) --> X >s 0 + // (X+MINSINT) <s X --> X >s (MAXSINT-MINSINT) --> X >s -1 + // (X+ -2) <s X --> X >s (MAXSINT- -2) --> X >s 126 + // (X+ -1) <s X --> X >s (MAXSINT- -1) --> X != 127 + if (Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_SLE) + return new ICmpInst(ICmpInst::ICMP_SGT, X, ConstantExpr::getSub(SMax, CI)); + + // (X+ 1) >s X --> X <s (MAXSINT-(1-1)) --> X != 127 + // (X+ 2) >s X --> X <s (MAXSINT-(2-1)) --> X <s 126 + // (X+MAXSINT) >s X --> X <s (MAXSINT-(MAXSINT-1)) --> X <s 1 + // (X+MINSINT) >s X --> X <s (MAXSINT-(MINSINT-1)) --> X <s -2 + // (X+ -2) >s X --> X <s (MAXSINT-(-2-1)) --> X <s -126 + // (X+ -1) >s X --> X <s (MAXSINT-(-1-1)) --> X == -128 + assert(Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_SGE); + Constant *C = ConstantInt::get(X->getContext(), CI->getValue()-1); + return new ICmpInst(ICmpInst::ICMP_SLT, X, ConstantExpr::getSub(SMax, C)); +} /// FoldICmpDivCst - Fold "icmp pred, ([su]div X, DivRHS), CmpRHS" where DivRHS /// and CmpRHS are both known to be integer constants. @@ -7077,8 +7149,7 @@ Instruction *InstCombiner::visitICmpInstWithInstAndIntCst(ICmpInst &ICI, break; case Instruction::Add: - // Fold: icmp pred (add, X, C1), C2 - + // Fold: icmp pred (add X, C1), C2 if (!ICI.isEquality()) { ConstantInt *LHSC = dyn_cast<ConstantInt>(LHSI->getOperand(1)); if (!LHSC) break; |