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Fold (iszero(A&K1) | iszero(A&K2)) -> (A&(K1|K2)) != (K1|K2) if we know that K1 and K2 are 'one-hot' (only one bit is on).

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llvm-svn: 194525
This commit is contained in:
Nadav Rotem 2013-11-12 22:38:59 +00:00
parent 8fbd606127
commit e15585e8ff
2 changed files with 85 additions and 3 deletions
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53
lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
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@ -1543,10 +1543,60 @@ static Instruction *MatchSelectFromAndOr(Value *A, Value *B,
return 0;
}
/// IsSingleBitValue - Returns true for "one-hot" values (values where at most
/// one bit can be set).
static bool IsOneHotValue(Value *V) {
// Match 1<<K.
if (BinaryOperator *BO = dyn_cast<BinaryOperator>(V))
if (BO->getOpcode() == Instruction::Shl) {
ConstantInt *One = dyn_cast<ConstantInt>(BO->getOperand(0));
return One && One->isOne();
}
// Check for power of two integer constants.
if (ConstantInt *K = dyn_cast<ConstantInt>(V))
return K->getValue().isPowerOf2();
return false;
}
/// FoldOrOfICmps - Fold (icmp)|(icmp) if possible.
Value *InstCombiner::FoldOrOfICmps(ICmpInst *LHS, ICmpInst *RHS) {
ICmpInst::Predicate LHSCC = LHS->getPredicate(), RHSCC = RHS->getPredicate();
// Fold (iszero(A & K1) | iszero(A & K2)) -> (A & (K1 | K2)) != (K1 | K2)
// if K1 and K2 are a one-bit mask.
ConstantInt *LHSCst = dyn_cast<ConstantInt>(LHS->getOperand(1));
ConstantInt *RHSCst = dyn_cast<ConstantInt>(RHS->getOperand(1));
if (LHS->getPredicate() == ICmpInst::ICMP_EQ && LHSCst && LHSCst->isZero() &&
RHS->getPredicate() == ICmpInst::ICMP_EQ && RHSCst && RHSCst->isZero()) {
BinaryOperator *LAnd = dyn_cast<BinaryOperator>(LHS->getOperand(0));
BinaryOperator *RAnd = dyn_cast<BinaryOperator>(RHS->getOperand(0));
if (LAnd && RAnd && LAnd->hasOneUse() && RHS->hasOneUse() &&
LAnd->getOpcode() == Instruction::And &&
RAnd->getOpcode() == Instruction::And) {
Value *Mask = 0;
Value *Masked = 0;
if (LAnd->getOperand(0) == RAnd->getOperand(0) &&
IsOneHotValue(LAnd->getOperand(1)) &&
IsOneHotValue(RAnd->getOperand(1))) {
Mask = Builder->CreateOr(LAnd->getOperand(1), RAnd->getOperand(1));
Masked = Builder->CreateAnd(LAnd->getOperand(0), Mask);
} else if (LAnd->getOperand(1) == RAnd->getOperand(1) &&
IsOneHotValue(LAnd->getOperand(0)) &&
IsOneHotValue(RAnd->getOperand(0))) {
Mask = Builder->CreateOr(LAnd->getOperand(0), RAnd->getOperand(0));
Masked = Builder->CreateAnd(LAnd->getOperand(1), Mask);
}
if (Masked)
return Builder->CreateICmp(ICmpInst::ICMP_NE, Masked, Mask);
}
}
// (icmp1 A, B) | (icmp2 A, B) --> (icmp3 A, B)
if (PredicatesFoldable(LHSCC, RHSCC)) {
if (LHS->getOperand(0) == RHS->getOperand(1) &&
@ -1567,9 +1617,6 @@ Value *InstCombiner::FoldOrOfICmps(ICmpInst *LHS, ICmpInst *RHS) {
return V;
Value *Val = LHS->getOperand(0), *Val2 = RHS->getOperand(0);
ConstantInt *LHSCst = dyn_cast<ConstantInt>(LHS->getOperand(1));
ConstantInt *RHSCst = dyn_cast<ConstantInt>(RHS->getOperand(1));
if (LHS->hasOneUse() || RHS->hasOneUse()) {
// (icmp eq B, 0) | (icmp ult A, B) -> (icmp ule A, B-1)
// (icmp eq B, 0) | (icmp ugt B, A) -> (icmp ule A, B-1)

35
test/Transforms/InstCombine/onehot_merge.ll Normal file
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@ -0,0 +1,35 @@
; RUN: opt < %s -instcombine -S | FileCheck %s
;CHECK: @and_consts
;CHECK: and i32 %k, 12
;CHECK: icmp ne i32 %0, 12
;CHECK: ret
define i1 @and_consts(i32 %k, i32 %c1, i32 %c2) {
bb:
%tmp1 = and i32 4, %k
%tmp2 = icmp eq i32 %tmp1, 0
%tmp5 = and i32 8, %k
%tmp6 = icmp eq i32 %tmp5, 0
%or = or i1 %tmp2, %tmp6
ret i1 %or
}
;CHECK: @foo1_and
;CHECK: shl i32 1, %c1
;CHECK-NEXT: shl i32 1, %c2
;CHECK-NEXT: or i32
;CHECK-NEXT: and i32
;CHECK-NEXT: icmp ne i32 %1, %0
;CHECK: ret
define i1 @foo1_and(i32 %k, i32 %c1, i32 %c2) {
bb:
%tmp = shl i32 1, %c1
%tmp4 = shl i32 1, %c2
%tmp1 = and i32 %tmp, %k
%tmp2 = icmp eq i32 %tmp1, 0
%tmp5 = and i32 %tmp4, %k
%tmp6 = icmp eq i32 %tmp5, 0
%or = or i1 %tmp2, %tmp6
ret i1 %or
}