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[SCEV] Fix applyLoopGuards() with range check idiom (PR51760)

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Due to a typo, this replaced %x with umax(C1, umin(C2, %x + C3))
rather than umax(C1, umin(C2, %x)). This didn't make a difference
for the existing tests, because the result is only used for range
calculation, and %x will usually have an unknown starting range,
and the additional offset keeps it unknown. However, if %x already
has a known range, we may compute a result range that is too
small.

(cherry picked from commit 8d54c8a0c3d7d4a50186ae7087780c6082e5bb46)
This commit is contained in:
Nikita Popov 2021-09-06 22:18:11 +02:00 committed by Tom Stellard
parent 8830999b87
commit 3c59cf5aa7
2 changed files with 41 additions and 1 deletions
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2
lib/Analysis/ScalarEvolution.cpp
View File

@ -13969,7 +13969,7 @@ const SCEV *ScalarEvolution::applyLoopGuards(const SCEV *Expr, const Loop *L) {
if (ExactRegion.isWrappedSet() || ExactRegion.isFullSet())
return false;
auto I = RewriteMap.find(LHSUnknown->getValue());
const SCEV *RewrittenLHS = I != RewriteMap.end() ? I->second : LHS;
const SCEV *RewrittenLHS = I != RewriteMap.end() ? I->second : LHSUnknown;
RewriteMap[LHSUnknown->getValue()] = getUMaxExpr(
getConstant(ExactRegion.getUnsignedMin()),
getUMinExpr(RewrittenLHS, getConstant(ExactRegion.getUnsignedMax())));

40
test/Analysis/ScalarEvolution/max-backedge-taken-count-guard-info.ll
View File

@ -1327,6 +1327,46 @@ exit:
ret void
}
; Same as @optimized_range_check_unsigned, but %N already has a range limited
; to [2,4) beforehand.
define void @optimized_range_check_unsigned3(i16* %pred, i1 %c) {
; CHECK-LABEL: 'optimized_range_check_unsigned3'
; CHECK-NEXT: Classifying expressions for: @optimized_range_check_unsigned3
; CHECK-NEXT: %N = select i1 %c, i32 2, i32 3
; CHECK-NEXT: --> %N U: [2,4) S: [2,4)
; CHECK-NEXT: %N.off = add i32 %N, -1
; CHECK-NEXT: --> (-1 + %N)<nsw> U: [1,3) S: [1,3)
; CHECK-NEXT: %iv = phi i32 [ 0, %entry ], [ %iv.next, %loop ]
; CHECK-NEXT: --> {0,+,1}<nuw><nsw><%loop> U: [0,3) S: [0,3) Exits: (-1 + %N)<nsw> LoopDispositions: { %loop: Computable }
; CHECK-NEXT: %gep = getelementptr inbounds i16, i16* %pred, i32 %iv
; CHECK-NEXT: --> {%pred,+,2}<nuw><%loop> U: full-set S: full-set Exits: ((2 * (zext i32 (-1 + %N)<nsw> to i64))<nuw><nsw> + %pred) LoopDispositions: { %loop: Computable }
; CHECK-NEXT: %iv.next = add nuw nsw i32 %iv, 1
; CHECK-NEXT: --> {1,+,1}<nuw><nsw><%loop> U: [1,4) S: [1,4) Exits: %N LoopDispositions: { %loop: Computable }
; CHECK-NEXT: Determining loop execution counts for: @optimized_range_check_unsigned3
; CHECK-NEXT: Loop %loop: backedge-taken count is (-1 + %N)<nsw>
; CHECK-NEXT: Loop %loop: max backedge-taken count is 2
; CHECK-NEXT: Loop %loop: Predicated backedge-taken count is (-1 + %N)<nsw>
; CHECK-NEXT: Predicates:
; CHECK: Loop %loop: Trip multiple is 1
;
entry:
%N = select i1 %c, i32 2, i32 3
%N.off = add i32 %N, -1
%cmp = icmp ult i32 %N.off, 7
br i1 %cmp, label %loop, label %exit
loop:
%iv = phi i32 [ 0, %entry ], [ %iv.next, %loop ]
%gep = getelementptr inbounds i16, i16* %pred, i32 %iv
store i16 0, i16* %gep, align 2
%iv.next = add nuw nsw i32 %iv, 1
%ec = icmp eq i32 %iv.next, %N
br i1 %ec, label %exit, label %loop
exit:
ret void
}
; Similar to @optimized_range_check_unsigned, but the initial compare checks
; against unsigned max (-1), which breaks the range check idiom.
define void @not_optimized_range_check_unsigned1(i16* %pred, i32 %N) {