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[InstCombine] foldUnsignedUnderflowCheck(): handle last few cases (PR43251) 

Summary:
I don't have a direct motivational case for this,
but it would be good to have this for completeness/symmetry.

This pattern is basically the motivational pattern from
https://bugs.llvm.org/show_bug.cgi?id=43251
but with different predicate that requires that the offset is non-zero.

The completeness bit comes from the fact that a similar pattern (offset != zero)
will be needed for https://bugs.llvm.org/show_bug.cgi?id=43259,
so it'd seem to be good to not overlook very similar patterns..

Proofs: https://rise4fun.com/Alive/21b

Also, there is something odd with `isKnownNonZero()`, if the non-zero
knowledge was specified as an assumption, it didn't pick it up (PR43267)

With this, i see no other missing folds for
https://bugs.llvm.org/show_bug.cgi?id=43251

Reviewers: spatel, nikic, xbolva00

Reviewed By: spatel

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D67412

llvm-svn: 372257
This commit is contained in:
Roman Lebedev 2019-09-18 20:10:07 +00:00
parent 366ab0d086
commit b646dd92c2
2 changed files with 60 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

52
llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
View File

@ -1049,6 +1049,44 @@ static Value *foldIsPowerOf2(ICmpInst *Cmp0, ICmpInst *Cmp1, bool JoinedByAnd,
return nullptr;
}
/// Commuted variants are assumed to be handled by calling this function again
/// with the parameters swapped.
static Value *foldUnsignedUnderflowCheck(ICmpInst *ZeroICmp,
ICmpInst *UnsignedICmp, bool IsAnd,
const SimplifyQuery &Q,
InstCombiner::BuilderTy &Builder) {
Value *Subtracted;
ICmpInst::Predicate EqPred;
if (!match(ZeroICmp, m_ICmp(EqPred, m_Value(Subtracted), m_Zero())) ||
!ICmpInst::isEquality(EqPred))
return nullptr;
Value *Base, *Offset;
if (!match(Subtracted, m_Sub(m_Value(Base), m_Value(Offset))))
return nullptr;
ICmpInst::Predicate UnsignedPred;
// Subtracted < Base && Subtracted != 0 --> Base > Offset iff Offset != 0
// Subtracted >= Base || Subtracted == 0 --> Base <= Base iff Offset != 0
if (match(UnsignedICmp,
m_c_ICmp(UnsignedPred, m_Specific(Subtracted), m_Specific(Base)))) {
if (UnsignedICmp->getOperand(0) != Subtracted)
UnsignedPred = ICmpInst::getSwappedPredicate(UnsignedPred);
if (UnsignedPred == ICmpInst::ICMP_ULT && IsAnd &&
EqPred == ICmpInst::ICMP_NE &&
isKnownNonZero(Offset, Q.DL, /*Depth=*/0, Q.AC, Q.CxtI, Q.DT))
return Builder.CreateICmpUGT(Base, Offset);
if (UnsignedPred == ICmpInst::ICMP_UGE && !IsAnd &&
EqPred == ICmpInst::ICMP_EQ &&
isKnownNonZero(Offset, Q.DL, /*Depth=*/0, Q.AC, Q.CxtI, Q.DT))
return Builder.CreateICmpULE(Base, Offset);
}
return nullptr;
}
/// Fold (icmp)&(icmp) if possible.
Value *InstCombiner::foldAndOfICmps(ICmpInst *LHS, ICmpInst *RHS,
Instruction &CxtI) {
@ -1094,6 +1132,13 @@ Value *InstCombiner::foldAndOfICmps(ICmpInst *LHS, ICmpInst *RHS,
if (Value *V = foldIsPowerOf2(LHS, RHS, true /* JoinedByAnd */, Builder))
return V;
if (Value *X =
foldUnsignedUnderflowCheck(LHS, RHS, /*IsAnd=*/true, SQ, Builder))
return X;
if (Value *X =
foldUnsignedUnderflowCheck(RHS, LHS, /*IsAnd=*/true, SQ, Builder))
return X;
// This only handles icmp of constants: (icmp1 A, C1) & (icmp2 B, C2).
Value *LHS0 = LHS->getOperand(0), *RHS0 = RHS->getOperand(0);
ConstantInt *LHSC = dyn_cast<ConstantInt>(LHS->getOperand(1));
@ -2196,6 +2241,13 @@ Value *InstCombiner::foldOrOfICmps(ICmpInst *LHS, ICmpInst *RHS,
if (Value *V = foldIsPowerOf2(LHS, RHS, false /* JoinedByAnd */, Builder))
return V;
if (Value *X =
foldUnsignedUnderflowCheck(LHS, RHS, /*IsAnd=*/false, SQ, Builder))
return X;
if (Value *X =
foldUnsignedUnderflowCheck(RHS, LHS, /*IsAnd=*/false, SQ, Builder))
return X;
// This only handles icmp of constants: (icmp1 A, C1) | (icmp2 B, C2).
if (!LHSC || !RHSC)
return nullptr;

16
llvm/test/Transforms/InstCombine/result-of-usub-is-non-zero-and-no-overflow.ll
View File

@ -296,8 +296,8 @@ define i1 @t10(i64 %base, i64* nonnull %offsetptr) {
; CHECK-NEXT: call void @use1(i1 [[NO_UNDERFLOW]])
; CHECK-NEXT: [[NOT_NULL:%.*]] = icmp ne i64 [[ADJUSTED]], 0
; CHECK-NEXT: call void @use1(i1 [[NOT_NULL]])
; CHECK-NEXT: [[R:%.*]] = and i1 [[NOT_NULL]], [[NO_UNDERFLOW]]
; CHECK-NEXT: ret i1 [[R]]
; CHECK-NEXT: [[TMP1:%.*]] = icmp ult i64 [[OFFSET]], [[BASE]]
; CHECK-NEXT: ret i1 [[TMP1]]
;
%offset = ptrtoint i64* %offsetptr to i64
@ -319,8 +319,8 @@ define i1 @t11_commutative(i64 %base, i64* nonnull %offsetptr) {
; CHECK-NEXT: call void @use1(i1 [[NO_UNDERFLOW]])
; CHECK-NEXT: [[NOT_NULL:%.*]] = icmp ne i64 [[ADJUSTED]], 0
; CHECK-NEXT: call void @use1(i1 [[NOT_NULL]])
; CHECK-NEXT: [[R:%.*]] = and i1 [[NOT_NULL]], [[NO_UNDERFLOW]]
; CHECK-NEXT: ret i1 [[R]]
; CHECK-NEXT: [[TMP1:%.*]] = icmp ult i64 [[OFFSET]], [[BASE]]
; CHECK-NEXT: ret i1 [[TMP1]]
;
%offset = ptrtoint i64* %offsetptr to i64
@ -343,8 +343,8 @@ define i1 @t12(i64 %base, i64* nonnull %offsetptr) {
; CHECK-NEXT: call void @use1(i1 [[NO_UNDERFLOW]])
; CHECK-NEXT: [[NOT_NULL:%.*]] = icmp eq i64 [[ADJUSTED]], 0
; CHECK-NEXT: call void @use1(i1 [[NOT_NULL]])
; CHECK-NEXT: [[R:%.*]] = or i1 [[NOT_NULL]], [[NO_UNDERFLOW]]
; CHECK-NEXT: ret i1 [[R]]
; CHECK-NEXT: [[TMP1:%.*]] = icmp uge i64 [[OFFSET]], [[BASE]]
; CHECK-NEXT: ret i1 [[TMP1]]
;
%offset = ptrtoint i64* %offsetptr to i64
@ -366,8 +366,8 @@ define i1 @t13(i64 %base, i64* nonnull %offsetptr) {
; CHECK-NEXT: call void @use1(i1 [[NO_UNDERFLOW]])
; CHECK-NEXT: [[NOT_NULL:%.*]] = icmp eq i64 [[ADJUSTED]], 0
; CHECK-NEXT: call void @use1(i1 [[NOT_NULL]])
; CHECK-NEXT: [[R:%.*]] = or i1 [[NOT_NULL]], [[NO_UNDERFLOW]]
; CHECK-NEXT: ret i1 [[R]]
; CHECK-NEXT: [[TMP1:%.*]] = icmp uge i64 [[OFFSET]], [[BASE]]
; CHECK-NEXT: ret i1 [[TMP1]]
;
%offset = ptrtoint i64* %offsetptr to i64