Skip to content

[ConstraintElim] Check if second op implies first for And. #75750

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 2 commits into from
Dec 20, 2023
Merged

[ConstraintElim] Check if second op implies first for And. #75750

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
3a1e1d5
[ConstraintElim] Check if second op implies first for And.
fhahn Dec 11, 2023
a314636
!fixup fix build bailure and add comment about Select check.
fhahn Dec 19, 2023
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
42 changes: 27 additions & 15 deletions llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -1365,16 +1365,27 @@ removeEntryFromStack(const StackEntry &E, ConstraintInfo &Info,
ReproducerCondStack.pop_back();
}

/// Check if the first condition for an AND implies the second.
static bool checkAndSecondOpImpliedByFirst(
FactOrCheck &CB, ConstraintInfo &Info, Module *ReproducerModule,
SmallVectorImpl<ReproducerEntry> &ReproducerCondStack,
SmallVectorImpl<StackEntry> &DFSInStack) {
/// Check if either the first condition of an AND is implied by the second or
/// vice versa.
static bool
checkAndOpImpliedByOther(FactOrCheck &CB, ConstraintInfo &Info,
Module *ReproducerModule,
SmallVectorImpl<ReproducerEntry> &ReproducerCondStack,
SmallVectorImpl<StackEntry> &DFSInStack) {

CmpInst::Predicate Pred;
Value *A, *B;
Instruction *And = CB.getContextInst();
if (!match(And->getOperand(0), m_ICmp(Pred, m_Value(A), m_Value(B))))
CmpInst *CmpToCheck = cast<CmpInst>(CB.getInstructionToSimplify());
unsigned OtherOpIdx = And->getOperand(0) == CmpToCheck ? 1 : 0;

// Don't try to simplify the first condition of a select by the second, as
// this may make the select more poisonous than the original one.
// TODO: check if the first operand may be poison.
if (OtherOpIdx != 0 && isa<SelectInst>(And))
Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Is this due to a poison-propagation issue?

Copy link
Contributor Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Yep, added a comment plus a TODO to check if the first op may be poison, thanks!

return false;

if (!match(And->getOperand(OtherOpIdx), m_ICmp(Pred, m_Value(A), m_Value(B))))
return false;

// Optimistically add fact from first condition.
Expand All @@ -1385,11 +1396,12 @@ static bool checkAndSecondOpImpliedByFirst(

bool Changed = false;
// Check if the second condition can be simplified now.
ICmpInst *Cmp = cast<ICmpInst>(And->getOperand(1));
if (auto ImpliedCondition = checkCondition(
Cmp->getPredicate(), Cmp->getOperand(0), Cmp->getOperand(1), Cmp,
Info, CB.NumIn, CB.NumOut, CB.getContextInst())) {
And->setOperand(1, ConstantInt::getBool(And->getType(), *ImpliedCondition));
if (auto ImpliedCondition =
checkCondition(CmpToCheck->getPredicate(), CmpToCheck->getOperand(0),
CmpToCheck->getOperand(1), CmpToCheck, Info, CB.NumIn,
CB.NumOut, CB.getContextInst())) {
And->setOperand(1 - OtherOpIdx,
ConstantInt::getBool(And->getType(), *ImpliedCondition));
Changed = true;
}

Expand Down Expand Up @@ -1609,11 +1621,11 @@ static bool eliminateConstraints(Function &F, DominatorTree &DT, LoopInfo &LI,
bool Simplified = checkAndReplaceCondition(
Cmp, Info, CB.NumIn, CB.NumOut, CB.getContextInst(),
ReproducerModule.get(), ReproducerCondStack, S.DT, ToRemove);
if (!Simplified && match(CB.getContextInst(),
m_LogicalAnd(m_Value(), m_Specific(Inst)))) {
if (!Simplified &&
match(CB.getContextInst(), m_LogicalAnd(m_Value(), m_Value()))) {
Simplified =
checkAndSecondOpImpliedByFirst(CB, Info, ReproducerModule.get(),
ReproducerCondStack, DFSInStack);
checkAndOpImpliedByOther(CB, Info, ReproducerModule.get(),
ReproducerCondStack, DFSInStack);
}
Changed |= Simplified;
}
Expand Down
8 changes: 4 additions & 4 deletions llvm/test/Transforms/ConstraintElimination/and-implied-by-operands.ll
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -31,7 +31,7 @@ define i1 @test_first_and_condition_implied_by_second_ops(i8 %x) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[C_1:%.*]] = icmp ugt i8 [[X:%.*]], 10
; CHECK-NEXT: [[T_1:%.*]] = icmp ugt i8 [[X]], 5
; CHECK-NEXT: [[AND:%.*]] = and i1 [[T_1]], [[C_1]]
; CHECK-NEXT: [[AND:%.*]] = and i1 true, [[C_1]]
; CHECK-NEXT: br i1 [[AND]], label [[THEN:%.*]], label [[ELSE:%.*]]
; CHECK: then:
; CHECK-NEXT: ret i1 false
Expand Down Expand Up @@ -105,7 +105,7 @@ define i1 @test_same_cond_for_and(i8 %x) {
; CHECK-LABEL: @test_same_cond_for_and(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[C_1:%.*]] = icmp ugt i8 [[X:%.*]], 10
; CHECK-NEXT: [[AND:%.*]] = and i1 [[C_1]], true
; CHECK-NEXT: [[AND:%.*]] = and i1 true, [[C_1]]
; CHECK-NEXT: br i1 [[AND]], label [[THEN:%.*]], label [[ELSE:%.*]]
; CHECK: then:
; CHECK-NEXT: ret i1 false
Expand All @@ -128,7 +128,7 @@ define i1 @test_same_cond_for_and_select_form(i8 %x) {
; CHECK-LABEL: @test_same_cond_for_and_select_form(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[C_1:%.*]] = icmp ugt i8 [[X:%.*]], 10
; CHECK-NEXT: [[AND:%.*]] = select i1 [[C_1]], i1 true, i1 false
; CHECK-NEXT: [[AND:%.*]] = select i1 [[C_1]], i1 [[C_1]], i1 false
Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Why did this regress?

Copy link
Contributor Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

In this case, both conds are the same, and in the new code we will try OtherOpIdx = 1 first, which then hits the early-exit condition for selects; Not sure if it is worth avoiding that and complicating the conditions.

; CHECK-NEXT: br i1 [[AND]], label [[THEN:%.*]], label [[ELSE:%.*]]
; CHECK: then:
; CHECK-NEXT: ret i1 false
Expand All @@ -152,7 +152,7 @@ define i1 @test_second_and_condition_not_implied_by_first(i8 %x) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[C_1:%.*]] = icmp ugt i8 [[X:%.*]], 10
; CHECK-NEXT: [[C_2:%.*]] = icmp ugt i8 [[X]], 5
; CHECK-NEXT: [[AND:%.*]] = and i1 [[C_2]], [[C_1]]
; CHECK-NEXT: [[AND:%.*]] = and i1 true, [[C_1]]
; CHECK-NEXT: br i1 [[AND]], label [[THEN:%.*]], label [[ELSE:%.*]]
; CHECK: then:
; CHECK-NEXT: ret i1 false
Expand Down
4 changes: 2 additions & 2 deletions llvm/test/Transforms/ConstraintElimination/and.ll
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -438,7 +438,7 @@ define i1 @test_and_chain_select_ule(i4 %x, i4 %y, i4 %z, i4 %a) {
; CHECK-NEXT: [[C_2:%.*]] = icmp ule i4 [[Y]], [[Z:%.*]]
; CHECK-NEXT: [[C_3:%.*]] = icmp ule i4 3, [[X]]
; CHECK-NEXT: [[C_4:%.*]] = icmp ule i4 3, [[A:%.*]]
; CHECK-NEXT: [[AND_1:%.*]] = select i1 [[C_1]], i1 true, i1 false
; CHECK-NEXT: [[AND_1:%.*]] = select i1 [[C_1]], i1 [[C_1]], i1 false
; CHECK-NEXT: [[AND_2:%.*]] = select i1 [[AND_1]], i1 [[C_3]], i1 false
; CHECK-NEXT: [[AND_3:%.*]] = select i1 [[C_4]], i1 [[AND_2]], i1 false
; CHECK-NEXT: br i1 [[AND_3]], label [[BB1:%.*]], label [[EXIT:%.*]]
Expand Down Expand Up @@ -522,7 +522,7 @@ define i1 @test_and_chain_select_ule_logical_or(i4 %x, i4 %y, i4 %z, i4 %a) {
; CHECK-NEXT: [[C_2:%.*]] = icmp ule i4 [[Y]], [[Z:%.*]]
; CHECK-NEXT: [[C_3:%.*]] = icmp ule i4 3, [[X]]
; CHECK-NEXT: [[C_4:%.*]] = icmp ule i4 3, [[A:%.*]]
; CHECK-NEXT: [[AND_1:%.*]] = select i1 [[C_1]], i1 true, i1 false
; CHECK-NEXT: [[AND_1:%.*]] = select i1 [[C_1]], i1 [[C_1]], i1 false
; CHECK-NEXT: [[AND_2:%.*]] = select i1 [[AND_1]], i1 [[C_3]], i1 false
; CHECK-NEXT: [[AND_3:%.*]] = select i1 [[C_4]], i1 [[AND_2]], i1 false
; CHECK-NEXT: [[AND_4:%.*]] = select i1 [[AND_3]], i1 true, i1 false
Expand Down
2 changes: 1 addition & 1 deletion llvm/test/Transforms/ConstraintElimination/gep-arithmetic-signed-predicates.ll
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -611,7 +611,7 @@ define i4 @ptr_N_signed_positive_assume(ptr %src, ptr %lower, ptr %upper, i16 %N
; CHECK: step.check:
; CHECK-NEXT: [[STEP_POS:%.*]] = icmp sge i16 [[STEP:%.*]], 0
; CHECK-NEXT: [[STEP_SLT_N:%.*]] = icmp slt i16 [[STEP]], [[N]]
; CHECK-NEXT: [[AND_STEP:%.*]] = and i1 [[STEP_POS]], false
; CHECK-NEXT: [[AND_STEP:%.*]] = and i1 false, [[STEP_SLT_N]]
; CHECK-NEXT: br i1 [[AND_STEP]], label [[PTR_CHECK:%.*]], label [[EXIT:%.*]]
; CHECK: ptr.check:
; CHECK-NEXT: [[SRC_STEP:%.*]] = getelementptr inbounds i8, ptr [[SRC]], i16 [[STEP]]
Expand Down
6 changes: 3 additions & 3 deletions llvm/test/Transforms/ConstraintElimination/geps-precondition-overflow-check.ll
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -36,7 +36,7 @@ define i1 @overflow_check_2_and(ptr %dst) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[DST_5:%.*]] = getelementptr i32, ptr [[DST:%.*]], i64 5
; CHECK-NEXT: [[DST_5_UGE:%.*]] = icmp uge ptr [[DST_5]], [[DST]]
; CHECK-NEXT: [[AND:%.*]] = and i1 [[DST_5_UGE]], true
; CHECK-NEXT: [[AND:%.*]] = and i1 true, [[DST_5_UGE]]
; CHECK-NEXT: br i1 [[AND]], label [[THEN:%.*]], label [[ELSE:%.*]]
; CHECK: then:
; CHECK-NEXT: [[DST_4:%.*]] = getelementptr i32, ptr [[DST]], i64 4
Expand Down Expand Up @@ -65,7 +65,7 @@ define i1 @overflow_check_3_and(ptr %dst) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[DST_5:%.*]] = getelementptr i32, ptr [[DST:%.*]], i64 5
; CHECK-NEXT: [[DST_5_UGE:%.*]] = icmp uge ptr [[DST_5]], [[DST]]
; CHECK-NEXT: [[AND:%.*]] = and i1 [[DST_5_UGE]], true
; CHECK-NEXT: [[AND:%.*]] = and i1 true, [[DST_5_UGE]]
; CHECK-NEXT: br i1 [[AND]], label [[THEN:%.*]], label [[ELSE:%.*]]
; CHECK: then:
; CHECK-NEXT: [[DST_4:%.*]] = getelementptr i32, ptr [[DST]], i64 4
Expand Down Expand Up @@ -98,7 +98,7 @@ define i1 @overflow_check_4_and(ptr %dst) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[DST_5:%.*]] = getelementptr i32, ptr [[DST:%.*]], i64 5
; CHECK-NEXT: [[DST_5_UGE:%.*]] = icmp uge ptr [[DST_5]], [[DST]]
; CHECK-NEXT: [[AND:%.*]] = and i1 [[DST_5_UGE]], true
; CHECK-NEXT: [[AND:%.*]] = and i1 true, [[DST_5_UGE]]
; CHECK-NEXT: br i1 [[AND]], label [[THEN:%.*]], label [[ELSE:%.*]]
; CHECK: then:
; CHECK-NEXT: [[DST_4:%.*]] = getelementptr i32, ptr [[DST]], i64 4
Expand Down