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[SCEV] Use loop guards when checking that RHS >= Start #75039

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Dec 12, 2023
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[SCEV] Use loop guards when checking that RHS >= Start #75039

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6 changes: 5 additions & 1 deletion llvm/lib/Analysis/ScalarEvolution.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -12910,7 +12910,11 @@ ScalarEvolution::howManyLessThans(const SCEV *LHS, const SCEV *RHS,
if (!BECount) {
auto canProveRHSGreaterThanEqualStart = [&]() {
auto CondGE = IsSigned ? ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE;
if (isLoopEntryGuardedByCond(L, CondGE, OrigRHS, OrigStart))
const SCEV *GuardedRHS = applyLoopGuards(OrigRHS, L);
const SCEV *GuardedStart = applyLoopGuards(OrigStart, L);

if (isLoopEntryGuardedByCond(L, CondGE, OrigRHS, OrigStart) ||
isKnownPredicate(CondGE, GuardedRHS, GuardedStart))
return true;

// (RHS > Start - 1) implies RHS >= Start.
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6 changes: 3 additions & 3 deletions llvm/test/Analysis/ScalarEvolution/trip-count.ll
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Expand Up @@ -127,10 +127,10 @@ leave:
define void @non_zero_from_loop_guard(i16 %n) {
; CHECK-LABEL: 'non_zero_from_loop_guard'
; CHECK-NEXT: Determining loop execution counts for: @non_zero_from_loop_guard
; CHECK-NEXT: Loop %loop: backedge-taken count is (-1 + (1 umax (%n /u 2)))<nsw>
; CHECK-NEXT: Loop %loop: backedge-taken count is (-1 + (%n /u 2))<nsw>
; CHECK-NEXT: Loop %loop: constant max backedge-taken count is 32766
; CHECK-NEXT: Loop %loop: symbolic max backedge-taken count is (-1 + (1 umax (%n /u 2)))<nsw>
; CHECK-NEXT: Loop %loop: Predicated backedge-taken count is (-1 + (1 umax (%n /u 2)))<nsw>
; CHECK-NEXT: Loop %loop: symbolic max backedge-taken count is (-1 + (%n /u 2))<nsw>
; CHECK-NEXT: Loop %loop: Predicated backedge-taken count is (-1 + (%n /u 2))<nsw>
; CHECK-NEXT: Predicates:
; CHECK-NEXT: Loop %loop: Trip multiple is 1
;
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