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Added select flavour for ABS and NEG(ABS)

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This patch can identify 
  ABS(X) ==> (X >s 0) ? X : -X and (X >s -1) ? X : -X
  ABS(X) ==> (X <s 0) ? -X : X and (X <s 1) ? -X : X
  NABS(X) ==> (X >s 0) ? -X : X and (X >s -1) ? -X : X
  NABS(X) ==> (X <s 0) ? X : -X and (X <s 1) ? X : -X
  
and can transform
  ABS(ABS(X)) -> ABS(X)
  NABS(NABS(X)) -> NABS(X)
  
Differential Revision: http://reviews.llvm.org/D3658



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210312 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dinesh Dwivedi
2014-06-06 06:54:45 +00:00
parent 7a0e6972ce
commit 2c3e3b491e
3 changed files with 532 additions and 20 deletions
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lib/Transforms/InstCombine/InstCombineSelect.cpp
+48 -18
View File
@@ -31,13 +31,18 @@ MatchSelectPattern(Value *V, Value *&LHS, Value *&RHS) {
ICmpInst *ICI = dyn_cast<ICmpInst>(SI->getCondition());
if (!ICI) return SPF_UNKNOWN;
LHS = ICI->getOperand(0);
RHS = ICI->getOperand(1);
ICmpInst::Predicate Pred = ICI->getPredicate();
Value *CmpLHS = ICI->getOperand(0);
Value *CmpRHS = ICI->getOperand(1);
Value *TrueVal = SI->getTrueValue();
Value *FalseVal = SI->getFalseValue();
LHS = CmpLHS;
RHS = CmpRHS;
// (icmp X, Y) ? X : Y
if (SI->getTrueValue() == ICI->getOperand(0) &&
SI->getFalseValue() == ICI->getOperand(1)) {
switch (ICI->getPredicate()) {
if (TrueVal == CmpLHS && FalseVal == CmpRHS) {
switch (Pred) {
default: return SPF_UNKNOWN; // Equality.
case ICmpInst::ICMP_UGT:
case ICmpInst::ICMP_UGE: return SPF_UMAX;
@@ -51,18 +56,35 @@ MatchSelectPattern(Value *V, Value *&LHS, Value *&RHS) {
}
// (icmp X, Y) ? Y : X
if (SI->getTrueValue() == ICI->getOperand(1) &&
SI->getFalseValue() == ICI->getOperand(0)) {
switch (ICI->getPredicate()) {
default: return SPF_UNKNOWN; // Equality.
case ICmpInst::ICMP_UGT:
case ICmpInst::ICMP_UGE: return SPF_UMIN;
case ICmpInst::ICMP_SGT:
case ICmpInst::ICMP_SGE: return SPF_SMIN;
case ICmpInst::ICMP_ULT:
case ICmpInst::ICMP_ULE: return SPF_UMAX;
case ICmpInst::ICMP_SLT:
case ICmpInst::ICMP_SLE: return SPF_SMAX;
if (TrueVal == CmpRHS && FalseVal == CmpLHS) {
switch (Pred) {
default: return SPF_UNKNOWN; // Equality.
case ICmpInst::ICMP_UGT:
case ICmpInst::ICMP_UGE: return SPF_UMIN;
case ICmpInst::ICMP_SGT:
case ICmpInst::ICMP_SGE: return SPF_SMIN;
case ICmpInst::ICMP_ULT:
case ICmpInst::ICMP_ULE: return SPF_UMAX;
case ICmpInst::ICMP_SLT:
case ICmpInst::ICMP_SLE: return SPF_SMAX;
}
}
if (ConstantInt *C1 = dyn_cast<ConstantInt>(CmpRHS)) {
if ((CmpLHS == TrueVal && match(FalseVal, m_Neg(m_Specific(CmpLHS)))) ||
(CmpLHS == FalseVal && match(TrueVal, m_Neg(m_Specific(CmpLHS))))) {
// ABS(X) ==> (X >s 0) ? X : -X and (X >s -1) ? X : -X
// NABS(X) ==> (X >s 0) ? -X : X and (X >s -1) ? -X : X
if (Pred == ICmpInst::ICMP_SGT && (C1->isZero() || C1->isMinusOne())) {
return (CmpLHS == TrueVal) ? SPF_ABS : SPF_NABS;
}
// ABS(X) ==> (X <s 0) ? -X : X and (X <s 1) ? -X : X
// NABS(X) ==> (X <s 0) ? X : -X and (X <s 1) ? X : -X
if (Pred == ICmpInst::ICMP_SLT && (C1->isZero() || C1->isOne())) {
return (CmpLHS == FalseVal) ? SPF_ABS : SPF_NABS;
}
}
}
@@ -704,6 +726,15 @@ Instruction *InstCombiner::FoldSPFofSPF(Instruction *Inner,
}
}
}
// ABS(ABS(X)) -> ABS(X)
// NABS(NABS(X)) -> NABS(X)
if (SPF1 == SPF2 && (SPF1 == SPF_ABS || SPF1 == SPF_NABS)) {
return ReplaceInstUsesWith(Outer, Inner);
}
// TODO: ABS(NABS(X)) -> ABS(X)
// TODO: NABS(ABS(X)) -> NABS(X)
return nullptr;
}
@@ -1008,7 +1039,6 @@ Instruction *InstCombiner::visitSelectInst(SelectInst &SI) {
// TODO.
// ABS(-X) -> ABS(X)
// ABS(ABS(X)) -> ABS(X)
}
// See if we can fold the select into a phi node if the condition is a select.