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[SCEV] Use guards to prove predicates
We can use calls to @llvm.experimental.guard to prove predicates, relying on the fact that in all locations domianted by a call to @llvm.experimental.guard the predicate it is guarding is known to be true. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@268997 91177308-0d34-0410-b5e6-96231b3b80d8
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Sanjoy Das
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@ -464,6 +464,12 @@ namespace llvm {
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///
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Function &F;
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/// Does the module have any calls to the llvm.experimental.guard intrinsic
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/// at all? If this is false, we avoid doing work that will only help if
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/// thare are guards present in the IR.
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///
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bool HasGuards;
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/// The target library information for the target we are targeting.
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///
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TargetLibraryInfo &TLI;
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@ -1007,6 +1013,11 @@ namespace llvm {
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const SCEV *FoundLHS,
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const SCEV *FoundRHS);
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/// Return true if the condition denoted by \p LHS \p Pred \p RHS is implied
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/// by a call to \c @llvm.experimental.guard in \p BB.
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bool isImpliedViaGuard(BasicBlock *BB, ICmpInst::Predicate Pred,
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const SCEV *LHS, const SCEV *RHS);
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/// Test whether the condition described by Pred, LHS, and RHS is true
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/// whenever the condition described by Pred, FoundLHS, and FoundRHS is
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/// true.
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@ -7805,6 +7805,23 @@ bool ScalarEvolution::isKnownPredicateViaSplitting(ICmpInst::Predicate Pred,
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isKnownPredicate(CmpInst::ICMP_SLT, LHS, RHS);
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}
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bool ScalarEvolution::isImpliedViaGuard(BasicBlock *BB,
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ICmpInst::Predicate Pred,
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const SCEV *LHS, const SCEV *RHS) {
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// No need to even try if we know the module has no guards.
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if (!HasGuards)
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return false;
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return any_of(*BB, [&](Instruction &I) {
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using namespace llvm::PatternMatch;
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Value *Condition;
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return match(&I, m_Intrinsic<Intrinsic::experimental_guard>(
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m_Value(Condition))) &&
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isImpliedCond(Pred, LHS, RHS, Condition, false);
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});
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}
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/// isLoopBackedgeGuardedByCond - Test whether the backedge of the loop is
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/// protected by a conditional between LHS and RHS. This is used to
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/// to eliminate casts.
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@ -7872,12 +7889,18 @@ ScalarEvolution::isLoopBackedgeGuardedByCond(const Loop *L,
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if (!DT.isReachableFromEntry(L->getHeader()))
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return false;
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if (isImpliedViaGuard(Latch, Pred, LHS, RHS))
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return true;
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for (DomTreeNode *DTN = DT[Latch], *HeaderDTN = DT[L->getHeader()];
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DTN != HeaderDTN; DTN = DTN->getIDom()) {
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assert(DTN && "should reach the loop header before reaching the root!");
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BasicBlock *BB = DTN->getBlock();
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if (isImpliedViaGuard(BB, Pred, LHS, RHS))
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return true;
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BasicBlock *PBB = BB->getSinglePredecessor();
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if (!PBB)
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continue;
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@ -7930,6 +7953,9 @@ ScalarEvolution::isLoopEntryGuardedByCond(const Loop *L,
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Pair.first;
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Pair = getPredecessorWithUniqueSuccessorForBB(Pair.first)) {
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if (isImpliedViaGuard(Pair.first, Pred, LHS, RHS))
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return true;
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BranchInst *LoopEntryPredicate =
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dyn_cast<BranchInst>(Pair.first->getTerminator());
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if (!LoopEntryPredicate ||
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@ -9462,11 +9488,26 @@ ScalarEvolution::ScalarEvolution(Function &F, TargetLibraryInfo &TLI,
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CouldNotCompute(new SCEVCouldNotCompute()),
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WalkingBEDominatingConds(false), ProvingSplitPredicate(false),
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ValuesAtScopes(64), LoopDispositions(64), BlockDispositions(64),
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FirstUnknown(nullptr) {}
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FirstUnknown(nullptr) {
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// To use guards for proving predicates, we need to scan every instruction in
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// relevant basic blocks, and not just terminators. Doing this is a waste of
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// time if the IR does not actually contain any calls to
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// @llvm.experimental.guard, so do a quick check and remember this beforehand.
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//
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// This pessimizes the case where a pass that preserves ScalarEvolution wants
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// to _add_ guards to the module when there weren't any before, and wants
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// ScalarEvolution to optimize based on those guards. For now we prefer to be
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// efficient in lieu of being smart in that rather obscure case.
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auto *GuardDecl = F.getParent()->getFunction(
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Intrinsic::getName(Intrinsic::experimental_guard));
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HasGuards = GuardDecl && !GuardDecl->use_empty();
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}
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ScalarEvolution::ScalarEvolution(ScalarEvolution &&Arg)
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: F(Arg.F), TLI(Arg.TLI), AC(Arg.AC), DT(Arg.DT), LI(Arg.LI),
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CouldNotCompute(std::move(Arg.CouldNotCompute)),
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: F(Arg.F), HasGuards(Arg.HasGuards), TLI(Arg.TLI), AC(Arg.AC), DT(Arg.DT),
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LI(Arg.LI), CouldNotCompute(std::move(Arg.CouldNotCompute)),
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ValueExprMap(std::move(Arg.ValueExprMap)),
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WalkingBEDominatingConds(false), ProvingSplitPredicate(false),
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BackedgeTakenCounts(std::move(Arg.BackedgeTakenCounts)),
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141
test/Analysis/ScalarEvolution/guards.ll
Normal file
141
test/Analysis/ScalarEvolution/guards.ll
Normal file
@ -0,0 +1,141 @@
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; RUN: opt -S -indvars < %s | FileCheck %s
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; Check that SCEV is able to recognize and use guards to prove
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; conditions gaurding loop entries and backedges. This isn't intended
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; to be a comprehensive test of SCEV's simplification capabilities,
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; tests directly testing e.g. if SCEV can elide a sext should go
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; elsewhere.
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target datalayout = "n8:16:32:64"
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declare void @llvm.experimental.guard(i1, ...)
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define void @test_1(i1* %cond_buf, i32* %len_buf) {
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; CHECK-LABEL: @test_1(
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entry:
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%len = load i32, i32* %len_buf, !range !{i32 1, i32 2147483648}
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br label %loop
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loop:
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; CHECK: loop:
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; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 true) [ "deopt"() ]
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; CHECK: %iv.inc.cmp = icmp slt i32 %iv.inc, %len
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; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 %iv.inc.cmp) [ "deopt"() ]
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; CHECK: leave:
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%iv = phi i32 [ 0, %entry ], [ %iv.inc, %loop ]
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%iv.inc = add i32 %iv, 1
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%iv.cmp = icmp slt i32 %iv, %len
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call void(i1, ...) @llvm.experimental.guard(i1 %iv.cmp) [ "deopt"() ]
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%iv.inc.cmp = icmp slt i32 %iv.inc, %len
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call void(i1, ...) @llvm.experimental.guard(i1 %iv.inc.cmp) [ "deopt"() ]
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%becond = load volatile i1, i1* %cond_buf
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br i1 %becond, label %loop, label %leave
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leave:
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ret void
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}
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define void @test_2(i32 %n, i32* %len_buf) {
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; CHECK-LABEL: @test_2(
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; CHECK: [[LEN_SEXT:%[^ ]+]] = sext i32 %len to i64
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; CHECK: br label %loop
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entry:
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%len = load i32, i32* %len_buf, !range !{i32 0, i32 2147483648}
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br label %loop
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loop:
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; CHECK: loop:
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; CHECK: %indvars.iv = phi i64 [ %indvars.iv.next, %loop ], [ 0, %entry ]
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; CHECK: %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
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; CHECK: %iv.inc.cmp = icmp slt i64 %indvars.iv.next, [[LEN_SEXT]]
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; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 %iv.inc.cmp) [ "deopt"() ]
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; CHECK: leave:
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%iv = phi i32 [ 0, %entry ], [ %iv.inc, %loop ]
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%iv.inc = add i32 %iv, 1
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%iv.sext = sext i32 %iv to i64
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%iv.inc.cmp = icmp slt i32 %iv.inc, %len
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call void(i1, ...) @llvm.experimental.guard(i1 %iv.inc.cmp) [ "deopt"() ]
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%becond = icmp ne i32 %iv, %n
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br i1 %becond, label %loop, label %leave
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leave:
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ret void
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}
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define void @test_3(i1* %cond_buf, i32* %len_buf) {
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; CHECK-LABEL: @test_3(
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entry:
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%len = load i32, i32* %len_buf
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%entry.cond = icmp sgt i32 %len, 0
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call void(i1, ...) @llvm.experimental.guard(i1 %entry.cond) [ "deopt"() ]
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br label %loop
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loop:
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; CHECK: loop:
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; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 true) [ "deopt"() ]
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; CHECK: %iv.inc.cmp = icmp slt i32 %iv.inc, %len
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; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 %iv.inc.cmp) [ "deopt"() ]
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; CHECK: leave:
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%iv = phi i32 [ 0, %entry ], [ %iv.inc, %loop ]
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%iv.inc = add i32 %iv, 1
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%iv.cmp = icmp slt i32 %iv, %len
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call void(i1, ...) @llvm.experimental.guard(i1 %iv.cmp) [ "deopt"() ]
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%iv.inc.cmp = icmp slt i32 %iv.inc, %len
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call void(i1, ...) @llvm.experimental.guard(i1 %iv.inc.cmp) [ "deopt"() ]
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%becond = load volatile i1, i1* %cond_buf
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br i1 %becond, label %loop, label %leave
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leave:
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ret void
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}
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define void @test_4(i1* %cond_buf, i32* %len_buf) {
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; CHECK-LABEL: @test_4(
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entry:
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%len = load i32, i32* %len_buf
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%entry.cond = icmp sgt i32 %len, 0
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call void(i1, ...) @llvm.experimental.guard(i1 %entry.cond) [ "deopt"() ]
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br label %loop
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loop:
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%iv = phi i32 [ 0, %entry ], [ %iv.inc, %be ]
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%iv.inc = add i32 %iv, 1
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%cond = load volatile i1, i1* %cond_buf
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br i1 %cond, label %left, label %be
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left:
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; Does not dominate the backedge, so cannot be used in the inductive proof
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%iv.inc.cmp = icmp slt i32 %iv.inc, %len
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call void(i1, ...) @llvm.experimental.guard(i1 %iv.inc.cmp) [ "deopt"() ]
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br label %be
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be:
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; CHECK: be:
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; CHECK-NEXT: %iv.cmp = icmp slt i32 %iv, %len
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; CHECK-NEXT: call void (i1, ...) @llvm.experimental.guard(i1 %iv.cmp) [ "deopt"() ]
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; CHECK: leave:
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%iv.cmp = icmp slt i32 %iv, %len
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call void(i1, ...) @llvm.experimental.guard(i1 %iv.cmp) [ "deopt"() ]
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%becond = load volatile i1, i1* %cond_buf
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br i1 %becond, label %loop, label %leave
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leave:
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ret void
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}
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