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InstSimplify: Optimize away useless unsigned comparisons

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Code like X < Y && Y == 0 should always be folded away to false.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223583 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer 2014-12-06 10:51:40 +00:00
parent c589098319
commit 620e8763ec
3 changed files with 98 additions and 1 deletions
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49
lib/Analysis/InstructionSimplify.cpp
View File

@ -1443,12 +1443,57 @@ Value *llvm::SimplifyAShrInst(Value *Op0, Value *Op1, bool isExact,
RecursionLimit);
}
static Value *simplifyUnsignedRangeCheck(ICmpInst *ZeroICmp,
ICmpInst *UnsignedICmp, bool IsAnd) {
Value *X, *Y;
ICmpInst::Predicate EqPred;
if (!match(ZeroICmp, m_ICmp(EqPred, m_Value(Y), m_Zero())) &&
ICmpInst::isEquality(EqPred))
return nullptr;
ICmpInst::Predicate UnsignedPred;
if (match(UnsignedICmp, m_ICmp(UnsignedPred, m_Value(X), m_Specific(Y))) &&
ICmpInst::isUnsigned(UnsignedPred))
;
else if (match(UnsignedICmp,
m_ICmp(UnsignedPred, m_Value(Y), m_Specific(X))) &&
ICmpInst::isUnsigned(UnsignedPred))
UnsignedPred = ICmpInst::getSwappedPredicate(UnsignedPred);
else
return nullptr;
// X < Y && Y != 0 --> X < Y
// X < Y || Y != 0 --> Y != 0
if (UnsignedPred == ICmpInst::ICMP_ULT && EqPred == ICmpInst::ICMP_NE)
return IsAnd ? UnsignedICmp : ZeroICmp;
// X >= Y || Y != 0 --> true
// X >= Y || Y == 0 --> X >= Y
if (UnsignedPred == ICmpInst::ICMP_UGE && !IsAnd) {
if (EqPred == ICmpInst::ICMP_NE)
return getTrue(UnsignedICmp->getType());
return UnsignedICmp;
}
// X < Y && Y == 0 --> false
if (UnsignedPred == ICmpInst::ICMP_ULT && EqPred == ICmpInst::ICMP_EQ &&
IsAnd)
return getFalse(UnsignedICmp->getType());
return nullptr;
}
// Simplify (and (icmp ...) (icmp ...)) to true when we can tell that the range
// of possible values cannot be satisfied.
static Value *SimplifyAndOfICmps(ICmpInst *Op0, ICmpInst *Op1) {
ICmpInst::Predicate Pred0, Pred1;
ConstantInt *CI1, *CI2;
Value *V;
if (Value *X = simplifyUnsignedRangeCheck(Op0, Op1, /*IsAnd=*/true))
return X;
if (!match(Op0, m_ICmp(Pred0, m_Add(m_Value(V), m_ConstantInt(CI1)),
m_ConstantInt(CI2))))
return nullptr;
@ -1602,6 +1647,10 @@ static Value *SimplifyOrOfICmps(ICmpInst *Op0, ICmpInst *Op1) {
ICmpInst::Predicate Pred0, Pred1;
ConstantInt *CI1, *CI2;
Value *V;
if (Value *X = simplifyUnsignedRangeCheck(Op0, Op1, /*IsAnd=*/false))
return X;
if (!match(Op0, m_ICmp(Pred0, m_Add(m_Value(V), m_ConstantInt(CI1)),
m_ConstantInt(CI2))))
return nullptr;

2
lib/IR/ConstantFold.cpp
View File

@ -1350,7 +1350,7 @@ static ICmpInst::Predicate areGlobalsPotentiallyEqual(const GlobalValue *GV1,
const GlobalValue *GV2) {
// Don't try to decide equality of aliases.
if (!isa<GlobalAlias>(GV1) && !isa<GlobalAlias>(GV2))
if (!GV1->hasExternalWeakLinkage() || !GV2->hasExternalWeakLinkage())
if (!GV1->hasExternalWeakLinkage() && !GV2->hasExternalWeakLinkage())
return ICmpInst::ICMP_NE;
return ICmpInst::BAD_ICMP_PREDICATE;
}

48
test/Transforms/InstSimplify/AndOrXor.ll
View File

@ -155,3 +155,51 @@ define i32 @neg_nuw(i32 %x) {
ret i32 %neg
; CHECK: ret i32 0
}
define i1 @and_icmp1(i32 %x, i32 %y) {
%1 = icmp ult i32 %x, %y
%2 = icmp ne i32 %y, 0
%3 = and i1 %1, %2
ret i1 %3
}
; CHECK-LABEL: @and_icmp1(
; CHECK: %[[cmp:.*]] = icmp ult i32 %x, %y
; CHECK: ret i1 %[[cmp]]
define i1 @and_icmp2(i32 %x, i32 %y) {
%1 = icmp ult i32 %x, %y
%2 = icmp eq i32 %y, 0
%3 = and i1 %1, %2
ret i1 %3
}
; CHECK-LABEL: @and_icmp2(
; CHECK: ret i1 false
define i1 @or_icmp1(i32 %x, i32 %y) {
%1 = icmp ult i32 %x, %y
%2 = icmp ne i32 %y, 0
%3 = or i1 %1, %2
ret i1 %3
}
; CHECK-LABEL: @or_icmp1(
; CHECK: %[[cmp:.*]] = icmp ne i32 %y, 0
; CHECK: ret i1 %[[cmp]]
define i1 @or_icmp2(i32 %x, i32 %y) {
%1 = icmp uge i32 %x, %y
%2 = icmp ne i32 %y, 0
%3 = or i1 %1, %2
ret i1 %3
}
; CHECK-LABEL: @or_icmp2(
; CHECK: ret i1 true
define i1 @or_icmp3(i32 %x, i32 %y) {
%1 = icmp uge i32 %x, %y
%2 = icmp eq i32 %y, 0
%3 = or i1 %1, %2
ret i1 %3
}
; CHECK-LABEL: @or_icmp3(
; CHECK: %[[cmp:.*]] = icmp uge i32 %x, %y
; CHECK: ret i1 %[[cmp]]