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Revert "[IndVars] Remove monotonic checks with unknown exit count" 

This reverts commit c6ca26c0bf.
This breaks stage2 builds due to hitting this assert:
```
   Assertion failed: (WeightSum <= UINT32_MAX && "Expected weights to scale down to 32 bits"), function calcMetadataWeights
```
when compiling AArch64RegisterBankInfo.cpp in LLVM.
This commit is contained in:
Raphael Isemann 2020-10-27 13:37:23 +01:00
parent a0d84d8031
commit e038b60d91
5 changed files with 16 additions and 105 deletions
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11
llvm/include/llvm/Analysis/ScalarEvolution.h
View File

@ -961,17 +961,6 @@ public:
const SCEV *&InvariantLHS,
const SCEV *&InvariantRHS);
/// Return true if the result of the predicate LHS `Pred` RHS is loop
/// invariant with respect to L at given Context during at least first
/// MaxIter iterations. Set InvariantPred, InvariantLHS and InvariantLHS so
/// that InvariantLHS `InvariantPred` InvariantRHS is the loop invariant form
/// of LHS `Pred` RHS. The predicate should be the loop's exit condition.
bool isLoopInvariantExitCondDuringFirstIterations(
ICmpInst::Predicate Pred, const SCEV *LHS, const SCEV *RHS, const Loop *L,
const Instruction *Context, const SCEV *MaxIter,
ICmpInst::Predicate &InvariantPred, const SCEV *&InvariantLHS,
const SCEV *&InvariantRHS);
/// Simplify LHS and RHS in a comparison with predicate Pred. Return true
/// iff any changes were made. If the operands are provably equal or
/// unequal, LHS and RHS are set to the same value and Pred is set to either

69
llvm/lib/Analysis/ScalarEvolution.cpp
View File

@ -9279,75 +9279,6 @@ bool ScalarEvolution::isLoopInvariantPredicate(
return true;
}
bool ScalarEvolution::isLoopInvariantExitCondDuringFirstIterations(
ICmpInst::Predicate Pred, const SCEV *LHS, const SCEV *RHS, const Loop *L,
const Instruction *Context, const SCEV *MaxIter,
ICmpInst::Predicate &InvariantPred, const SCEV *&InvariantLHS,
const SCEV *&InvariantRHS) {
// Try to prove the following set of facts:
// - The predicate is monotonic.
// - If the check does not fail on the 1st iteration:
// - No overflow will happen during first MaxIter iterations;
// - It will not fail on the MaxIter'th iteration.
// If the check does fail on the 1st iteration, we leave the loop and no
// other checks matter.
// If there is a loop-invariant, force it into the RHS, otherwise bail out.
if (!isLoopInvariant(RHS, L)) {
if (!isLoopInvariant(LHS, L))
return false;
std::swap(LHS, RHS);
Pred = ICmpInst::getSwappedPredicate(Pred);
}
auto *AR = dyn_cast<SCEVAddRecExpr>(LHS);
// TODO: Lift affinity limitation in the future.
if (!AR || AR->getLoop() != L || !AR->isAffine())
return false;
// The predicate must be relational (i.e. <, <=, >=, >).
if (!ICmpInst::isRelational(Pred))
return false;
// TODO: Support steps other than +/- 1.
const SCEV *Step = AR->getOperand(1);
auto *One = getOne(Step->getType());
auto *MinusOne = getNegativeSCEV(One);
if (Step != One && Step != MinusOne)
return false;
// Type mismatch here means that MaxIter is potentially larger than max
// unsigned value in start type, which mean we cannot prove no wrap for the
// indvar.
if (AR->getType() != MaxIter->getType())
return false;
// Value of IV on suggested last iteration.
const SCEV *Last = AR->evaluateAtIteration(MaxIter, *this);
// Does it still meet the requirement?
if (!isKnownPredicateAt(Pred, Last, RHS, Context))
return false;
// Because step is +/- 1 and MaxIter has same type as Start (i.e. it does
// not exceed max unsigned value of this type), this effectively proves
// that there is no wrap during the iteration. To prove that there is no
// signed/unsigned wrap, we need to check that
// Start <= Last for step = 1 or Start >= Last for step = -1.
ICmpInst::Predicate NoOverflowPred =
CmpInst::isSigned(Pred) ? ICmpInst::ICMP_SLE : ICmpInst::ICMP_ULE;
if (Step == MinusOne)
NoOverflowPred = CmpInst::getSwappedPredicate(NoOverflowPred);
const SCEV *Start = AR->getStart();
if (!isKnownPredicateAt(NoOverflowPred, Start, Last, Context))
return false;
// Everything is fine.
InvariantPred = Pred;
InvariantLHS = Start;
InvariantRHS = RHS;
return true;
}
bool ScalarEvolution::isKnownPredicateViaConstantRanges(
ICmpInst::Predicate Pred, const SCEV *LHS, const SCEV *RHS) {
if (HasSameValue(LHS, RHS))

26
llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
View File

@ -2307,9 +2307,9 @@ bool IndVarSimplify::sinkUnusedInvariants(Loop *L) {
}
// Returns true if the condition of \p BI being checked is invariant and can be
// proved to be trivially true during at least first \p MaxIter iterations.
// proved to be trivially true.
static bool isTrivialCond(const Loop *L, BranchInst *BI, ScalarEvolution *SE,
bool ProvingLoopExit, const SCEV *MaxIter) {
bool ProvingLoopExit) {
ICmpInst::Predicate Pred;
Value *LHS, *RHS;
using namespace PatternMatch;
@ -2335,20 +2335,7 @@ static bool isTrivialCond(const Loop *L, BranchInst *BI, ScalarEvolution *SE,
if (SE->isKnownPredicateAt(Pred, LHSS, RHSS, BI))
return true;
if (ProvingLoopExit)
return false;
ICmpInst::Predicate InvariantPred;
const SCEV *InvariantLHS, *InvariantRHS;
// Check if there is a loop-invariant predicate equivalent to our check.
if (!SE->isLoopInvariantExitCondDuringFirstIterations(
Pred, LHSS, RHSS, L, BI, MaxIter, InvariantPred, InvariantLHS,
InvariantRHS))
return false;
// Can we prove it to be trivially true?
return SE->isKnownPredicateAt(InvariantPred, InvariantLHS, InvariantRHS, BI);
return false;
}
bool IndVarSimplify::optimizeLoopExits(Loop *L, SCEVExpander &Rewriter) {
@ -2429,15 +2416,14 @@ bool IndVarSimplify::optimizeLoopExits(Loop *L, SCEVExpander &Rewriter) {
// Okay, we do not know the exit count here. Can we at least prove that it
// will remain the same within iteration space?
auto *BI = cast<BranchInst>(ExitingBB->getTerminator());
auto OptimizeCond = [&](bool Inverted, const SCEV *MaxIter) {
if (isTrivialCond(L, BI, SE, Inverted, MaxIter)) {
auto OptimizeCond = [&](bool Inverted) {
if (isTrivialCond(L, BI, SE, Inverted)) {
FoldExit(ExitingBB, Inverted);
return true;
}
return false;
};
if (OptimizeCond(false, MaxExitCount) ||
OptimizeCond(true, MaxExitCount))
if (OptimizeCond(false) || OptimizeCond(true))
Changed = true;
continue;
}

12
llvm/test/Transforms/IndVarSimplify/monotonic_checks.ll
View File

@ -12,7 +12,8 @@ define i32 @test_01(i32* %p) {
; CHECK: loop:
; CHECK-NEXT: [[IV:%.*]] = phi i32 [ [[LEN]], [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[BACKEDGE:%.*]] ]
; CHECK-NEXT: [[IV_NEXT]] = add nsw i32 [[IV]], -1
; CHECK-NEXT: br i1 true, label [[BACKEDGE]], label [[FAIL:%.*]]
; CHECK-NEXT: [[RC:%.*]] = icmp slt i32 [[IV_NEXT]], [[LEN]]
; CHECK-NEXT: br i1 [[RC]], label [[BACKEDGE]], label [[FAIL:%.*]]
; CHECK: backedge:
; CHECK-NEXT: [[LOOP_COND:%.*]] = icmp ne i32 [[IV]], 0
; CHECK-NEXT: br i1 [[LOOP_COND]], label [[LOOP]], label [[EXIT:%.*]]
@ -92,7 +93,8 @@ define i32 @test_02(i32* %p) {
; CHECK: loop:
; CHECK-NEXT: [[IV:%.*]] = phi i32 [ [[LEN]], [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[BACKEDGE:%.*]] ]
; CHECK-NEXT: [[IV_NEXT]] = add i32 [[IV]], 1
; CHECK-NEXT: br i1 true, label [[BACKEDGE]], label [[FAIL:%.*]]
; CHECK-NEXT: [[RC:%.*]] = icmp sgt i32 [[IV_NEXT]], [[LEN]]
; CHECK-NEXT: br i1 [[RC]], label [[BACKEDGE]], label [[FAIL:%.*]]
; CHECK: backedge:
; CHECK-NEXT: [[LOOP_COND:%.*]] = icmp ne i32 [[IV]], 0
; CHECK-NEXT: br i1 [[LOOP_COND]], label [[LOOP]], label [[EXIT:%.*]]
@ -170,7 +172,8 @@ define i32 @test_03(i32* %p) {
; CHECK: loop:
; CHECK-NEXT: [[IV:%.*]] = phi i32 [ [[LEN]], [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[BACKEDGE:%.*]] ]
; CHECK-NEXT: [[IV_NEXT]] = add nuw nsw i32 [[IV]], 1
; CHECK-NEXT: br i1 true, label [[BACKEDGE]], label [[FAIL:%.*]]
; CHECK-NEXT: [[RC:%.*]] = icmp ugt i32 [[IV_NEXT]], [[LEN]]
; CHECK-NEXT: br i1 [[RC]], label [[BACKEDGE]], label [[FAIL:%.*]]
; CHECK: backedge:
; CHECK-NEXT: [[LOOP_COND:%.*]] = icmp ne i32 [[IV]], 1000
; CHECK-NEXT: br i1 [[LOOP_COND]], label [[LOOP]], label [[EXIT:%.*]]
@ -208,7 +211,8 @@ define i32 @test_04(i32* %p) {
; CHECK: loop:
; CHECK-NEXT: [[IV:%.*]] = phi i32 [ [[LEN]], [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[BACKEDGE:%.*]] ]
; CHECK-NEXT: [[IV_NEXT]] = add nsw i32 [[IV]], -1
; CHECK-NEXT: br i1 true, label [[BACKEDGE]], label [[FAIL:%.*]]
; CHECK-NEXT: [[RC:%.*]] = icmp slt i32 [[IV_NEXT]], [[LEN]]
; CHECK-NEXT: br i1 [[RC]], label [[BACKEDGE]], label [[FAIL:%.*]]
; CHECK: backedge:
; CHECK-NEXT: [[LOOP_COND:%.*]] = icmp ne i32 [[IV]], 0
; CHECK-NEXT: br i1 [[LOOP_COND]], label [[LOOP]], label [[EXIT:%.*]]

3
llvm/test/Transforms/IndVarSimplify/predicated_ranges.ll
View File

@ -71,7 +71,8 @@ define void @test_predicated_simple_signed(i32* %p, i32* %arr) {
; CHECK-NEXT: br i1 [[ZERO_COND]], label [[EXIT:%.*]], label [[RANGE_CHECK_BLOCK:%.*]]
; CHECK: range_check_block:
; CHECK-NEXT: [[IV_NEXT]] = sub i32 [[IV]], 1
; CHECK-NEXT: br i1 true, label [[BACKEDGE]], label [[FAIL:%.*]]
; CHECK-NEXT: [[RANGE_CHECK:%.*]] = icmp slt i32 [[IV_NEXT]], [[LEN]]
; CHECK-NEXT: br i1 [[RANGE_CHECK]], label [[BACKEDGE]], label [[FAIL:%.*]]
; CHECK: backedge:
; CHECK-NEXT: [[EL_PTR:%.*]] = getelementptr i32, i32* [[P]], i32 [[IV]]
; CHECK-NEXT: [[EL:%.*]] = load i32, i32* [[EL_PTR]], align 4