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Optimize all cases of "icmp (X+Cst), X" to something simpler. This triggers

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a bunch in lencode, ldecod, spass, 176.gcc, 252.eon, among others.  It is 
also the first part of PR5822

llvm-svn: 91811
This commit is contained in:
Chris Lattner 2009-12-21 03:19:28 +00:00
parent 072f39fd3a
commit d34eb29977
2 changed files with 111 additions and 3 deletions
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77
lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -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;

37
test/Transforms/InstCombine/icmp.ll
View File

@ -62,3 +62,40 @@ define i32 @test6(i32 %a, i32 %b) {
; CHECK-NEXT: %f = and i32 %e, %b
; CHECK-NEXT: ret i32 %f
}
define i1 @test7(i32 %x) {
entry:
%a = add i32 %x, -1
%b = icmp ult i32 %a, %x
ret i1 %b
; CHECK: %b = icmp ne i32 %x, 0
; CHECK: ret i1 %b
}
define i1 @test8(i32 %x){
entry:
%a = add i32 %x, -1
%b = icmp eq i32 %a, %x
ret i1 %b
; CHECK: ret i1 false
}
define i1 @test9(i32 %x) {
entry:
%a = add i32 %x, -2
%b = icmp ugt i32 %x, %a
ret i1 %b
; CHECK: icmp ugt i32 %x, 1
; CHECK: ret i1 %b
}
define i1 @test10(i32 %x){
entry:
%a = add i32 %x, -1
%b = icmp slt i32 %a, %x
ret i1 %b
; CHECK: %b = icmp ne i32 %x, -2147483648
; CHECK: ret i1 %b
}