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[SCEV] Collect conditions from assumes same way as for branches. 

Also collect conditions from assume up-front in applyLoopGuards.
This allows re-using the logic to handle logical ANDs as assume
conditions.

It should should pave the road for a fix for #55645.
This commit is contained in:
Florian Hahn 2022-05-26 18:16:37 +01:00
parent 917dc0749b
commit 6af5f5697c
No known key found for this signature in database
GPG Key ID: EEF712BB5E80EBBA
2 changed files with 17 additions and 19 deletions
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28
llvm/lib/Analysis/ScalarEvolution.cpp
View File

@ -14518,12 +14518,23 @@ const SCEV *ScalarEvolution::applyLoopGuards(const SCEV *Expr, const Loop *L) {
ExprsToRewrite.push_back(LHS);
}
};
// First, collect conditions from dominating branches. Starting at the loop
SmallVector<std::pair<Value *, bool>> Terms;
// First, collect information from assumptions dominating the loop.
for (auto &AssumeVH : AC.assumptions()) {
if (!AssumeVH)
continue;
auto *AssumeI = cast<CallInst>(AssumeVH);
if (!DT.dominates(AssumeI, L->getHeader()))
continue;
Terms.emplace_back(AssumeI->getOperand(0), true);
}
// Second, collect conditions from dominating branches. Starting at the loop
// predecessor, climb up the predecessor chain, as long as there are
// predecessors that can be found that have unique successors leading to the
// original header.
// TODO: share this logic with isLoopEntryGuardedByCond.
SmallVector<std::pair<Value *, bool>> Terms;
for (std::pair<const BasicBlock *, const BasicBlock *> Pair(
L->getLoopPredecessor(), L->getHeader());
Pair.first; Pair = getPredecessorWithUniqueSuccessorForBB(Pair.first)) {
@ -14570,19 +14581,6 @@ const SCEV *ScalarEvolution::applyLoopGuards(const SCEV *Expr, const Loop *L) {
}
}
// Also collect information from assumptions dominating the loop.
for (auto &AssumeVH : AC.assumptions()) {
if (!AssumeVH)
continue;
auto *AssumeI = cast<CallInst>(AssumeVH);
auto *Cmp = dyn_cast<ICmpInst>(AssumeI->getOperand(0));
if (!Cmp || !DT.dominates(AssumeI, L->getHeader()))
continue;
const auto *LHS = getSCEV(Cmp->getOperand(0));
const auto *RHS = getSCEV(Cmp->getOperand(1));
CollectCondition(Cmp->getPredicate(), LHS, RHS, RewriteMap);
}
if (RewriteMap.empty())
return Expr;

8
llvm/test/Analysis/ScalarEvolution/max-backedge-taken-count-guard-info.ll
View File

@ -825,14 +825,14 @@ define void @test_guard_assume_and(i32* nocapture readonly %data, i64 %count) {
; CHECK-NEXT: %cmp.and = and i1 %cmp.ult, %cmp.ne
; CHECK-NEXT: --> (%cmp.ult umin %cmp.ne) U: full-set S: full-set
; CHECK-NEXT: %iv = phi i64 [ %iv.next, %loop ], [ 0, %entry ]
; CHECK-NEXT: --> {0,+,1}<nuw><%loop> U: [0,-1) S: [0,-1) Exits: (-1 + %count) LoopDispositions: { %loop: Computable }
; CHECK-NEXT: --> {0,+,1}<nuw><%loop> U: [0,4) S: [0,4) Exits: (-1 + %count) LoopDispositions: { %loop: Computable }
; CHECK-NEXT: %idx = getelementptr inbounds i32, i32* %data, i64 %iv
; CHECK-NEXT: --> {%data,+,4}<%loop> U: full-set S: full-set Exits: (-4 + (4 * %count) + %data) LoopDispositions: { %loop: Computable }
; CHECK-NEXT: --> {%data,+,4}<nuw><%loop> U: full-set S: full-set Exits: (-4 + (4 * %count) + %data) LoopDispositions: { %loop: Computable }
; CHECK-NEXT: %iv.next = add nuw i64 %iv, 1
; CHECK-NEXT: --> {1,+,1}<nuw><%loop> U: [1,0) S: [1,0) Exits: %count LoopDispositions: { %loop: Computable }
; CHECK-NEXT: --> {1,+,1}<nuw><%loop> U: [1,5) S: [1,5) Exits: %count LoopDispositions: { %loop: Computable }
; CHECK-NEXT: Determining loop execution counts for: @test_guard_assume_and
; CHECK-NEXT: Loop %loop: backedge-taken count is (-1 + %count)
; CHECK-NEXT: Loop %loop: max backedge-taken count is -2
; CHECK-NEXT: Loop %loop: max backedge-taken count is 3
; CHECK-NEXT: Loop %loop: Predicated backedge-taken count is (-1 + %count)
; CHECK-NEXT: Predicates:
; CHECK: Loop %loop: Trip multiple is 1