Re-apply [SCEV] Fix isLoopEntryGuardedByCond usage
ScalarEvolution::isKnownPredicate invokes isLoopEntryGuardedByCond without check that SCEV is available at entry point of the loop. It is incorrect and fixed by patch. To bugs additionally fixed: assert is moved after the check whether loop is not a nullptr. Usage of isLoopEntryGuardedByCond in ScalarEvolution::isImpliedCondOperandsViaNoOverflow is guarded by isAvailableAtLoopEntry. Reviewers: sanjoy, mkazantsev, anna, dorit, reames Reviewed By: mkazantsev Subscribers: llvm-commits Differential Revision: https://reviews.llvm.org/D42417 llvm-svn: 324204
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@ -8669,7 +8669,8 @@ bool ScalarEvolution::isKnownPredicate(ICmpInst::Predicate Pred,
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bool RightGuarded = false;
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if (LAR) {
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const Loop *L = LAR->getLoop();
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if (isLoopEntryGuardedByCond(L, Pred, LAR->getStart(), RHS) &&
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if (isAvailableAtLoopEntry(RHS, L) &&
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isLoopEntryGuardedByCond(L, Pred, LAR->getStart(), RHS) &&
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isLoopBackedgeGuardedByCond(L, Pred, LAR->getPostIncExpr(*this), RHS)) {
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if (!RAR) return true;
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LeftGuarded = true;
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@ -8677,7 +8678,8 @@ bool ScalarEvolution::isKnownPredicate(ICmpInst::Predicate Pred,
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}
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if (RAR) {
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const Loop *L = RAR->getLoop();
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if (isLoopEntryGuardedByCond(L, Pred, LHS, RAR->getStart()) &&
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if (isAvailableAtLoopEntry(LHS, L) &&
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isLoopEntryGuardedByCond(L, Pred, LHS, RAR->getStart()) &&
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isLoopBackedgeGuardedByCond(L, Pred, LHS, RAR->getPostIncExpr(*this))) {
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if (!LAR) return true;
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RightGuarded = true;
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@ -9062,6 +9064,12 @@ ScalarEvolution::isLoopEntryGuardedByCond(const Loop *L,
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// (interprocedural conditions notwithstanding).
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if (!L) return false;
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// Both LHS and RHS must be available at loop entry.
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assert(isAvailableAtLoopEntry(LHS, L) &&
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"LHS is not available at Loop Entry");
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assert(isAvailableAtLoopEntry(RHS, L) &&
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"RHS is not available at Loop Entry");
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if (isKnownPredicateViaConstantRanges(Pred, LHS, RHS))
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return true;
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@ -9418,7 +9426,8 @@ bool ScalarEvolution::isImpliedCondOperandsViaNoOverflow(
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}
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// Try to prove (1) or (2), as needed.
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return isLoopEntryGuardedByCond(L, Pred, FoundRHS,
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return isAvailableAtLoopEntry(FoundRHS, L) &&
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isLoopEntryGuardedByCond(L, Pred, FoundRHS,
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getConstant(FoundRHSLimit));
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}
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@ -934,9 +934,9 @@ LoopStructure::parseLoopStructure(ScalarEvolution &SE,
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return None;
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}
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if (!SE.isLoopEntryGuardedByCond(
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&L, BoundPred, IndVarStart,
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SE.getAddExpr(RightSCEV, Step))) {
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if (!SE.isAvailableAtLoopEntry(RightSCEV, &L) ||
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!SE.isLoopEntryGuardedByCond(&L, BoundPred, IndVarStart,
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SE.getAddExpr(RightSCEV, Step))) {
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FailureReason = "Induction variable start not bounded by upper limit";
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return None;
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}
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@ -948,7 +948,8 @@ LoopStructure::parseLoopStructure(ScalarEvolution &SE,
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RightValue = B.CreateAdd(RightValue, One);
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}
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} else {
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if (!SE.isLoopEntryGuardedByCond(&L, BoundPred, IndVarStart, RightSCEV)) {
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if (!SE.isAvailableAtLoopEntry(RightSCEV, &L) ||
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!SE.isLoopEntryGuardedByCond(&L, BoundPred, IndVarStart, RightSCEV)) {
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FailureReason = "Induction variable start not bounded by upper limit";
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return None;
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}
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@ -1014,9 +1015,10 @@ LoopStructure::parseLoopStructure(ScalarEvolution &SE,
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return None;
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}
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if (!SE.isLoopEntryGuardedByCond(
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&L, BoundPred, IndVarStart,
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SE.getMinusSCEV(RightSCEV, SE.getOne(RightSCEV->getType())))) {
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if (!SE.isAvailableAtLoopEntry(RightSCEV, &L) ||
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!SE.isLoopEntryGuardedByCond(
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&L, BoundPred, IndVarStart,
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SE.getMinusSCEV(RightSCEV, SE.getOne(RightSCEV->getType())))) {
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FailureReason = "Induction variable start not bounded by lower limit";
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return None;
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}
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@ -1028,7 +1030,8 @@ LoopStructure::parseLoopStructure(ScalarEvolution &SE,
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RightValue = B.CreateSub(RightValue, One);
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}
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} else {
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if (!SE.isLoopEntryGuardedByCond(&L, BoundPred, IndVarStart, RightSCEV)) {
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if (!SE.isAvailableAtLoopEntry(RightSCEV, &L) ||
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!SE.isLoopEntryGuardedByCond(&L, BoundPred, IndVarStart, RightSCEV)) {
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FailureReason = "Induction variable start not bounded by lower limit";
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return None;
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}
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@ -0,0 +1,54 @@
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; RUN: opt < %s -indvars -S | FileCheck %s
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; This is regression test for the bug in ScalarEvolution::isKnownPredicate.
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; It does not check whether SCEV is available at loop entry before invoking
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; and utility function isLoopEntryGuardedByCond and that leads to miscompile.
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target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128-ni:1"
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target triple = "x86_64-unknown-linux-gnu"
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declare void @foo(i64)
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declare void @bar(i32)
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define void @test(i8* %arr) {
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entry:
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br label %outer_header
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outer_header:
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%i = phi i32 [40, %entry], [%i.next, %outer_latch]
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%i.64 = sext i32 %i to i64
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br label %inner_header
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inner_header:
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%j = phi i32 [27, %outer_header], [%j.next, %inner_backedge]
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%j1 = zext i32 %j to i64
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; The next 4 lines are required for avoid widening of %j and
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; SCEV at %cmp would not be AddRec.
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%gep = getelementptr inbounds i8, i8* %arr, i64 %j1
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%ld = load i8, i8* %gep
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%ec = icmp eq i8 %ld, 0
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br i1 %ec, label %return, label %inner_backedge
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inner_backedge:
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%cmp = icmp ult i32 %j, %i
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%s = select i1 %cmp, i32 %i, i32 %j
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; Select should not be simplified because if
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; %i == 26 and %j == 27, %s should be equal to %j.
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; In case of a bug the instruction is simplified to
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; %s = select i1 true, i32 %0, i32 %j
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; CHECK-NOT: %s = select i1 true
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call void @bar(i32 %s)
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%j.next = add nsw i32 %j, -2
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%cond = icmp ult i32 %j, 3
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br i1 %cond, label %outer_latch, label %inner_header
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outer_latch:
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%i.next = add i32 %i, -1
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%cond2 = icmp sgt i32 %i.next, 13
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; This line is just for forcing widening of %i
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call void @foo(i64 %i.64)
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br i1 %cond2, label %outer_header, label %return
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return:
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ret void
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}
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