[llvm] r303875 - NewGVN: Fix PR 33119, PR 33129, due to regressed undef handling
Daniel Berlin via llvm-commits
llvm-commits at lists.llvm.org
Thu May 25 08:44:20 PDT 2017
Author: dannyb
Date: Thu May 25 10:44:20 2017
New Revision: 303875
URL: http://llvm.org/viewvc/llvm-project?rev=303875&view=rev
Log:
NewGVN: Fix PR 33119, PR 33129, due to regressed undef handling
Fix PR33120 and others by eliminating self-cycles a different way.
Modified:
llvm/trunk/lib/Transforms/Scalar/NewGVN.cpp
llvm/trunk/test/Transforms/NewGVN/pr32403.ll
Modified: llvm/trunk/lib/Transforms/Scalar/NewGVN.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/NewGVN.cpp?rev=303875&r1=303874&r2=303875&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/NewGVN.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/NewGVN.cpp Thu May 25 10:44:20 2017
@@ -858,7 +858,14 @@ PHIExpression *NewGVN::createPHIExpressi
// Filter out unreachable phi operands.
auto Filtered = make_filter_range(PHIOperands, [&](const Use *U) {
- return ReachableEdges.count({PN->getIncomingBlock(*U), PHIBlock});
+ if (*U == PN)
+ return false;
+ if (!ReachableEdges.count({PN->getIncomingBlock(*U), PHIBlock}))
+ return false;
+ // Things in TOPClass are equivalent to everything.
+ if (ValueToClass.lookup(*U) == TOPClass)
+ return false;
+ return true;
});
std::transform(Filtered.begin(), Filtered.end(), op_inserter(E),
[&](const Use *U) -> Value * {
@@ -866,14 +873,6 @@ PHIExpression *NewGVN::createPHIExpressi
HasBackedge = HasBackedge || isBackedge(BB, PHIBlock);
OriginalOpsConstant =
OriginalOpsConstant && isa<Constant>(*U);
- // Use nullptr to distinguish between things that were
- // originally self-defined and those that have an operand
- // leader that is self-defined.
- if (*U == PN)
- return nullptr;
- // Things in TOPClass are equivalent to everything.
- if (ValueToClass.lookup(*U) == TOPClass)
- return nullptr;
return lookupOperandLeader(*U);
});
return E;
@@ -1585,6 +1584,30 @@ bool NewGVN::isCycleFree(const Instructi
// Evaluate PHI nodes symbolically, and create an expression result.
const Expression *NewGVN::performSymbolicPHIEvaluation(Instruction *I) const {
+ // Resolve irreducible and reducible phi cycles.
+ // FIXME: This is hopefully a temporary solution while we resolve the issues
+ // with fixpointing self-cycles. It currently should be "guaranteed" to be
+ // correct, but non-optimal. The SCCFinder does not, for example, take
+ // reachability of arguments into account, etc.
+ SCCFinder.Start(I);
+ bool CanOptimize = true;
+ SmallPtrSet<Value *, 8> OuterOps;
+
+ auto &Component = SCCFinder.getComponentFor(I);
+ for (auto *Member : Component) {
+ if (!isa<PHINode>(Member)) {
+ CanOptimize = false;
+ break;
+ }
+ for (auto &PHIOp : cast<PHINode>(Member)->operands())
+ if (!isa<PHINode>(PHIOp) || !Component.count(cast<PHINode>(PHIOp)))
+ OuterOps.insert(PHIOp);
+ }
+ if (CanOptimize && OuterOps.size() == 1) {
+ DEBUG(dbgs() << "Resolving cyclic phi to value " << *(*OuterOps.begin())
+ << "\n");
+ return createVariableOrConstant(*OuterOps.begin());
+ }
// True if one of the incoming phi edges is a backedge.
bool HasBackedge = false;
// All constant tracks the state of whether all the *original* phi operands
@@ -1598,17 +1621,7 @@ const Expression *NewGVN::performSymboli
// See if all arguments are the same.
// We track if any were undef because they need special handling.
bool HasUndef = false;
- bool CycleFree = isCycleFree(I);
auto Filtered = make_filter_range(E->operands(), [&](Value *Arg) {
- if (Arg == nullptr)
- return false;
- // Original self-operands are already eliminated during expression creation.
- // We can only eliminate value-wise self-operands if it's cycle
- // free. Otherwise, eliminating the operand can cause our value to change,
- // which can cause us to not eliminate the operand, which changes the value
- // back to what it was before, cycling forever.
- if (CycleFree && Arg == I)
- return false;
if (isa<UndefValue>(Arg)) {
HasUndef = true;
return false;
@@ -1617,6 +1630,14 @@ const Expression *NewGVN::performSymboli
});
// If we are left with no operands, it's dead.
if (Filtered.begin() == Filtered.end()) {
+ // If it has undef at this point, it means there are no-non-undef arguments,
+ // and thus, the value of the phi node must be undef.
+ if (HasUndef) {
+ DEBUG(dbgs() << "PHI Node " << *I
+ << " has no non-undef arguments, valuing it as undef\n");
+ return createConstantExpression(UndefValue::get(I->getType()));
+ }
+
DEBUG(dbgs() << "No arguments of PHI node " << *I << " are live\n");
deleteExpression(E);
return createDeadExpression();
@@ -1646,7 +1667,7 @@ const Expression *NewGVN::performSymboli
// constants, or all operands are ignored but the undef, it also must be
// cycle free.
if (!AllConstant && HasBackedge && NumOps > 0 &&
- !isa<UndefValue>(AllSameValue) && !CycleFree)
+ !isa<UndefValue>(AllSameValue) && !isCycleFree(I))
return E;
// Only have to check for instructions
@@ -3560,6 +3581,7 @@ bool NewGVN::eliminateInstructions(Funct
// Map to store the use counts
DenseMap<const Value *, unsigned int> UseCounts;
for (auto *CC : reverse(CongruenceClasses)) {
+ DEBUG(dbgs() << "Eliminating in congruence class " << CC->getID() << "\n");
// Track the equivalent store info so we can decide whether to try
// dead store elimination.
SmallVector<ValueDFS, 8> PossibleDeadStores;
@@ -3606,8 +3628,6 @@ bool NewGVN::eliminateInstructions(Funct
}
CC->swap(MembersLeft);
} else {
- DEBUG(dbgs() << "Eliminating in congruence class " << CC->getID()
- << "\n");
// If this is a singleton, we can skip it.
if (CC->size() != 1 || RealToTemp.lookup(Leader)) {
// This is a stack because equality replacement/etc may place
Modified: llvm/trunk/test/Transforms/NewGVN/pr32403.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/NewGVN/pr32403.ll?rev=303875&r1=303874&r2=303875&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/NewGVN/pr32403.ll (original)
+++ llvm/trunk/test/Transforms/NewGVN/pr32403.ll Thu May 25 10:44:20 2017
@@ -17,7 +17,8 @@ define void @reorder_ref_pic_list() loca
; CHECK-NEXT: [[INC_I:%.*]] = add nsw i32 [[REFIDXLX_0]], 1
; CHECK-NEXT: br label [[FOR_BODY8_I:%.*]]
; CHECK: for.body8.i:
-; CHECK-NEXT: br i1 undef, label [[FOR_INC24_I:%.*]], label [[IF_THEN17_I:%.*]]
+; CHECK-NEXT: [[NIDX_052_I:%.*]] = phi i32 [ [[INC_I]], [[IF_THEN13]] ], [ [[NIDX_052_I]], [[FOR_INC24_I:%.*]] ]
+; CHECK-NEXT: br i1 undef, label [[FOR_INC24_I]], label [[IF_THEN17_I:%.*]]
; CHECK: if.then17.i:
; CHECK-NEXT: br label [[FOR_INC24_I]]
; CHECK: for.inc24.i:
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