[llvm] r372257 - [InstCombine] foldUnsignedUnderflowCheck(): handle last few cases (PR43251)
Roman Lebedev via llvm-commits
llvm-commits at lists.llvm.org
Wed Sep 18 13:10:07 PDT 2019
Author: lebedevri
Date: Wed Sep 18 13:10:07 2019
New Revision: 372257
URL: http://llvm.org/viewvc/llvm-project?rev=372257&view=rev
Log:
[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
Modified:
llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
llvm/trunk/test/Transforms/InstCombine/result-of-usub-is-non-zero-and-no-overflow.ll
Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp?rev=372257&r1=372256&r2=372257&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp Wed Sep 18 13:10:07 2019
@@ -1049,6 +1049,44 @@ static Value *foldIsPowerOf2(ICmpInst *C
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(ICmp
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(ICmpI
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;
Modified: llvm/trunk/test/Transforms/InstCombine/result-of-usub-is-non-zero-and-no-overflow.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/result-of-usub-is-non-zero-and-no-overflow.ll?rev=372257&r1=372256&r2=372257&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/result-of-usub-is-non-zero-and-no-overflow.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/result-of-usub-is-non-zero-and-no-overflow.ll Wed Sep 18 13:10:07 2019
@@ -296,8 +296,8 @@ define i1 @t10(i64 %base, i64* nonnull %
; 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, i6
; 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 %
; 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 %
; 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
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