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ValueTracking: generalize isNonEqualPHIs #108820

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9a3f743
ValueTracking: generalize isNonEqualPHIs
artagnon Sep 16, 2024
fb1933c
ValueTracking: avoid compile-time blowup
artagnon Sep 16, 2024
62c0f62
ValueTracking: fix thinko, crash; add test
artagnon Sep 25, 2024
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25 changes: 9 additions & 16 deletions llvm/lib/Analysis/ValueTracking.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2697,11 +2697,6 @@ static bool isNonZeroSub(const APInt &DemandedElts, unsigned Depth,
if (matchOpWithOpEqZero(X, Y))
return true;

// TODO: Move this case into isKnownNonEqual().
if (auto *C = dyn_cast<Constant>(X))
if (C->isNullValue() && isKnownNonZero(Y, DemandedElts, Q, Depth))
return true;

return ::isKnownNonEqual(X, Y, DemandedElts, Depth, Q);
}

Expand Down Expand Up @@ -3537,25 +3532,17 @@ static bool isNonEqualPHIs(const PHINode *PN1, const PHINode *PN2,
return false;

SmallPtrSet<const BasicBlock *, 8> VisitedBBs;
bool UsedFullRecursion = false;
for (const BasicBlock *IncomBB : PN1->blocks()) {
if (!VisitedBBs.insert(IncomBB).second)
continue; // Don't reprocess blocks that we have dealt with already.
const Value *IV1 = PN1->getIncomingValueForBlock(IncomBB);
const Value *IV2 = PN2->getIncomingValueForBlock(IncomBB);
const APInt *C1, *C2;
if (match(IV1, m_APInt(C1)) && match(IV2, m_APInt(C2)) && *C1 != *C2)
continue;

// Only one pair of phi operands is allowed for full recursion.
if (UsedFullRecursion)
return false;

const unsigned PhiRecursionLimit =
std::max(Depth + 1, MaxAnalysisRecursionDepth - 2);
SimplifyQuery RecQ = Q.getWithoutCondContext();
RecQ.CxtI = IncomBB->getTerminator();
if (!isKnownNonEqual(IV1, IV2, DemandedElts, Depth + 1, RecQ))
if (!isKnownNonEqual(IV1, IV2, DemandedElts, PhiRecursionLimit, RecQ))
return false;
UsedFullRecursion = true;
}
return true;
}
Expand Down Expand Up @@ -3642,6 +3629,12 @@ static bool isKnownNonEqual(const Value *V1, const Value *V2,
// We can't look through casts yet.
return false;

if (isa<Constant>(V2))
std::swap(V1, V2);
if (auto *C = dyn_cast<Constant>(V1))
if (C->isNullValue() && isKnownNonZero(V2, DemandedElts, Q, Depth))
return true;

if (Depth >= MaxAnalysisRecursionDepth)
return false;

Expand Down
76 changes: 76 additions & 0 deletions llvm/test/Analysis/ValueTracking/known-non-equal.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -316,6 +316,82 @@ exit:
ret i1 %cmp
}

define i1 @known_non_equal_phis2(i8 %p, i8 %n) {
; CHECK-LABEL: @known_non_equal_phis2(
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[A:%.*]] = phi i8 [ 0, [[ENTRY:%.*]] ], [ [[NEXT:%.*]], [[LOOP]] ]
; CHECK-NEXT: [[NEXT]] = add nsw i8 [[A]], 2
; CHECK-NEXT: [[CMP1:%.*]] = icmp eq i8 [[A]], [[N:%.*]]
; CHECK-NEXT: br i1 [[CMP1]], label [[EXIT:%.*]], label [[LOOP]]
; CHECK: exit:
; CHECK-NEXT: ret i1 true
;
entry:
%known.nonzero = add nuw i8 %p, 1
br label %loop
loop:
%A = phi i8 [ 0, %entry ], [ %next, %loop ]
%B = phi i8 [ %known.nonzero, %entry ], [ %A, %loop ]
%next = add nsw i8 %A, 2
%cmp1 = icmp eq i8 %A, %n
br i1 %cmp1, label %exit, label %loop
exit:
%cmp = icmp ne i8 %A, %B
ret i1 %cmp
}

define i1 @phi_max_recursion_limit(i1 %cond, i32 %switch.cond) {
; CHECK-LABEL: @phi_max_recursion_limit(
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[BB0:%.*]]
; CHECK: bb0:
; CHECK-NEXT: [[PHIA_0:%.*]] = phi i32 [ [[PHIA_1:%.*]], [[BB1:%.*]] ], [ 0, [[ENTRY:%.*]] ]
; CHECK-NEXT: [[PHIB_0:%.*]] = phi i32 [ [[PHIB_1:%.*]], [[BB1]] ], [ 0, [[ENTRY]] ]
; CHECK-NEXT: br i1 [[COND:%.*]], label [[SWITCH_BLOCK:%.*]], label [[EXIT:%.*]]
; CHECK: switch.block:
; CHECK-NEXT: switch i32 [[SWITCH_COND:%.*]], label [[BB1]] [
; CHECK-NEXT: i32 0, label [[EPILOGUE:%.*]]
; CHECK-NEXT: i32 1, label [[EPILOGUE]]
; CHECK-NEXT: ]
; CHECK: bb1:
; CHECK-NEXT: [[PHIA_1]] = phi i32 [ [[PHIA_0]], [[SWITCH_BLOCK]] ], [ 0, [[EPILOGUE]] ]
; CHECK-NEXT: [[PHIB_1]] = phi i32 [ [[PHIB_0]], [[SWITCH_BLOCK]] ], [ 0, [[EPILOGUE]] ]
; CHECK-NEXT: br label [[BB0]]
; CHECK: epilogue:
; CHECK-NEXT: br label [[BB1]]
; CHECK: exit:
; CHECK-NEXT: [[RET:%.*]] = icmp eq i32 [[PHIA_0]], [[PHIB_0]]
; CHECK-NEXT: ret i1 [[RET]]
;
entry:
br label %bb0

bb0:
%phiA.0 = phi i32 [ %phiA.1, %bb1 ], [ 0, %entry ]
%phiB.0 = phi i32 [ %phiB.1, %bb1 ], [ 0, %entry ]
br i1 %cond, label %switch.block, label %exit

switch.block:
switch i32 %switch.cond, label %bb1 [
i32 0, label %epilogue
i32 1, label %epilogue
]

bb1:
%phiA.1 = phi i32 [ %phiA.0, %switch.block ], [ 0, %epilogue ]
%phiB.1 = phi i32 [ %phiB.0, %switch.block ], [ 0, %epilogue ]
br label %bb0

epilogue:
br label %bb1

exit:
%ret = icmp eq i32 %phiA.0, %phiB.0
ret i1 %ret
}

define i1 @known_non_equal_phis_fail(i8 %p, ptr %pq, i8 %n, i8 %r) {
; CHECK-LABEL: @known_non_equal_phis_fail(
; CHECK-NEXT: entry:
Expand Down