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[SCEV] Reorder operands checks in collectConditions.

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The initial two cases require a SCEVConstant as RHS. Pull up the condition
to check and swap SCEVConstants from below. Also remove a redundant
check & swap if RHS is SCEVUnknown.
This commit is contained in:
Florian Hahn 2021-11-18 09:36:16 +00:00
parent dd6281c4c1
commit da9f2ba3b1
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GPG Key ID: EEF712BB5E80EBBA
3 changed files with 30 additions and 33 deletions
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55
llvm/lib/Analysis/ScalarEvolution.cpp
View File

@ -13774,26 +13774,8 @@ const SCEV *ScalarEvolution::applyLoopGuards(const SCEV *Expr, const Loop *L) {
// SCEV. In particular, using contextual facts to imply flags is *NOT*
// legal. See the scoping rules for flags in the header to understand why.
// If we have LHS == 0, check if LHS is computing a property of some unknown
// SCEV %v which we can rewrite %v to express explicitly.
const SCEVConstant *RHSC = dyn_cast<SCEVConstant>(RHS);
if (Predicate == CmpInst::ICMP_EQ && RHSC &&
RHSC->getValue()->isNullValue()) {
// If LHS is A % B, i.e. A % B == 0, rewrite A to (A /u B) * B to
// explicitly express that.
const SCEV *URemLHS = nullptr;
const SCEV *URemRHS = nullptr;
if (matchURem(LHS, URemLHS, URemRHS)) {
if (const SCEVUnknown *LHSUnknown = dyn_cast<SCEVUnknown>(URemLHS)) {
auto Multiple = getMulExpr(getUDivExpr(URemLHS, URemRHS), URemRHS);
RewriteMap[LHSUnknown] = Multiple;
ExprsToRewrite.push_back(LHSUnknown);
return;
}
}
}
if (!isa<SCEVUnknown>(LHS) && isa<SCEVUnknown>(RHS)) {
// If LHS is a constant, apply information to the other expression.
if (isa<SCEVConstant>(LHS)) {
std::swap(LHS, RHS);
Predicate = CmpInst::getSwappedPredicate(Predicate);
}
@ -13831,20 +13813,35 @@ const SCEV *ScalarEvolution::applyLoopGuards(const SCEV *Expr, const Loop *L) {
if (MatchRangeCheckIdiom())
return;
// If RHS is SCEVUnknown, make sure the information is applied to it.
if (isa<SCEVUnknown>(RHS)) {
std::swap(LHS, RHS);
Predicate = CmpInst::getSwappedPredicate(Predicate);
}
// If LHS is a constant, apply information to the other expression.
if (isa<SCEVConstant>(LHS)) {
std::swap(LHS, RHS);
Predicate = CmpInst::getSwappedPredicate(Predicate);
// If we have LHS == 0, check if LHS is computing a property of some unknown
// SCEV %v which we can rewrite %v to express explicitly.
const SCEVConstant *RHSC = dyn_cast<SCEVConstant>(RHS);
if (Predicate == CmpInst::ICMP_EQ && RHSC &&
RHSC->getValue()->isNullValue()) {
// If LHS is A % B, i.e. A % B == 0, rewrite A to (A /u B) * B to
// explicitly express that.
const SCEV *URemLHS = nullptr;
const SCEV *URemRHS = nullptr;
if (matchURem(LHS, URemLHS, URemRHS)) {
if (const SCEVUnknown *LHSUnknown = dyn_cast<SCEVUnknown>(URemLHS)) {
auto Multiple = getMulExpr(getUDivExpr(URemLHS, URemRHS), URemRHS);
RewriteMap[LHSUnknown] = Multiple;
ExprsToRewrite.push_back(LHSUnknown);
return;
}
}
}
// Do not apply information for constants or if RHS contains an AddRec.
if (isa<SCEVConstant>(LHS) || containsAddRecurrence(RHS))
return;
// If RHS is SCEVUnknown, make sure the information is applied to it.
if (!isa<SCEVUnknown>(LHS) && isa<SCEVUnknown>(RHS)) {
std::swap(LHS, RHS);
Predicate = CmpInst::getSwappedPredicate(Predicate);
}
// Limit to expressions that can be rewritten.
if (!isa<SCEVUnknown>(LHS) && !isa<SCEVZeroExtendExpr>(LHS))
return;

6
llvm/test/Analysis/ScalarEvolution/max-backedge-taken-count-guard-info.ll
View File

@ -1295,14 +1295,14 @@ define void @optimized_range_check_unsigned_icmp_ops_swapped(i16* %pred, i32 %N)
; CHECK-NEXT: %N.off = add i32 %N, -1
; CHECK-NEXT: --> (-1 + %N) U: full-set S: full-set
; CHECK-NEXT: %iv = phi i32 [ 0, %entry ], [ %iv.next, %loop ]
; CHECK-NEXT: --> {0,+,1}<nuw><nsw><%loop> U: [0,-2147483648) S: [0,-2147483648) Exits: (-1 + %N) LoopDispositions: { %loop: Computable }
; CHECK-NEXT: --> {0,+,1}<nuw><nsw><%loop> U: [0,7) S: [0,7) Exits: (-1 + %N) 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) 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,-2147483648) S: [1,-2147483648) Exits: %N LoopDispositions: { %loop: Computable }
; CHECK-NEXT: --> {1,+,1}<nuw><nsw><%loop> U: [1,8) S: [1,8) Exits: %N LoopDispositions: { %loop: Computable }
; CHECK-NEXT: Determining loop execution counts for: @optimized_range_check_unsigned_icmp_ops_swapped
; CHECK-NEXT: Loop %loop: backedge-taken count is (-1 + %N)
; CHECK-NEXT: Loop %loop: max backedge-taken count is -1
; CHECK-NEXT: Loop %loop: max backedge-taken count is 6
; CHECK-NEXT: Loop %loop: Predicated backedge-taken count is (-1 + %N)
; CHECK-NEXT: Predicates:
; CHECK: Loop %loop: Trip multiple is 1

2
llvm/test/Analysis/ScalarEvolution/trip-multiple-guard-info.ll
View File

@ -34,7 +34,7 @@ define void @test_trip_multiple_4_icmp_ops_swapped(i32 %num) {
; CHECK: Loop %for.body: backedge-taken count is (-1 + %num)
; CHECK-NEXT: Loop %for.body: max backedge-taken count is -2
; CHECK-NEXT: Loop %for.body: Predicated backedge-taken count is (-1 + %num)
; CHECK: Loop %for.body: Trip multiple is 1
; CHECK: Loop %for.body: Trip multiple is 4
;
entry:
%u = urem i32 %num, 4