diff options
Diffstat (limited to 'lib/CodeGen')
| -rw-r--r-- | lib/CodeGen/RegisterCoalescer.cpp | 45 |
1 files changed, 37 insertions, 8 deletions
diff --git a/lib/CodeGen/RegisterCoalescer.cpp b/lib/CodeGen/RegisterCoalescer.cpp index b5d80032ae..36d8101422 100644 --- a/lib/CodeGen/RegisterCoalescer.cpp +++ b/lib/CodeGen/RegisterCoalescer.cpp @@ -1282,8 +1282,18 @@ class JoinVals { // Value in the other live range that overlaps this def, if any. VNInfo *OtherVNI; - // Is this value an IMPLICIT_DEF? - bool IsImplicitDef; + // Is this value an IMPLICIT_DEF that can be erased? + // + // IMPLICIT_DEF values should only exist at the end of a basic block that + // is a predecessor to a phi-value. These IMPLICIT_DEF instructions can be + // safely erased if they are overlapping a live value in the other live + // interval. + // + // Weird control flow graphs and incomplete PHI handling in + // ProcessImplicitDefs can very rarely create IMPLICIT_DEF values with + // longer live ranges. Such IMPLICIT_DEF values should be treated like + // normal values. + bool ErasableImplicitDef; // True when the live range of this value will be pruned because of an // overlapping CR_Replace value in the other live range. @@ -1293,8 +1303,8 @@ class JoinVals { bool PrunedComputed; Val() : Resolution(CR_Keep), WriteLanes(0), ValidLanes(0), - RedefVNI(0), OtherVNI(0), IsImplicitDef(false), Pruned(false), - PrunedComputed(false) {} + RedefVNI(0), OtherVNI(0), ErasableImplicitDef(false), + Pruned(false), PrunedComputed(false) {} bool isAnalyzed() const { return WriteLanes != 0; } }; @@ -1432,7 +1442,10 @@ JoinVals::analyzeValue(unsigned ValNo, JoinVals &Other) { // An IMPLICIT_DEF writes undef values. if (DefMI->isImplicitDef()) { - V.IsImplicitDef = true; + // We normally expect IMPLICIT_DEF values to be live only until the end + // of their block. If the value is really live longer and gets pruned in + // another block, this flag is cleared again. + V.ErasableImplicitDef = true; V.ValidLanes &= ~V.WriteLanes; } } @@ -1485,7 +1498,22 @@ JoinVals::analyzeValue(unsigned ValNo, JoinVals &Other) { // We have overlapping values, or possibly a kill of Other. // Recursively compute assignments up the dominator tree. Other.computeAssignment(V.OtherVNI->id, *this); - const Val &OtherV = Other.Vals[V.OtherVNI->id]; + Val &OtherV = Other.Vals[V.OtherVNI->id]; + + // Check if OtherV is an IMPLICIT_DEF that extends beyond its basic block. + // This shouldn't normally happen, but ProcessImplicitDefs can leave such + // IMPLICIT_DEF instructions behind, and there is nothing wrong with it + // technically. + // + // WHen it happens, treat that IMPLICIT_DEF as a normal value, and don't try + // to erase the IMPLICIT_DEF instruction. + if (OtherV.ErasableImplicitDef && DefMI && + DefMI->getParent() != Indexes->getMBBFromIndex(V.OtherVNI->def)) { + DEBUG(dbgs() << "IMPLICIT_DEF defined at " << V.OtherVNI->def + << " extends into BB#" << DefMI->getParent()->getNumber() + << ", keeping it.\n"); + OtherV.ErasableImplicitDef = false; + } // Allow overlapping PHI values. Any real interference would show up in a // predecessor, the PHI itself can't introduce any conflicts. @@ -1794,7 +1822,8 @@ void JoinVals::pruneValues(JoinVals &Other, // predecessors, so the instruction should simply go away once its value // has been replaced. Val &OtherV = Other.Vals[Vals[i].OtherVNI->id]; - bool EraseImpDef = OtherV.IsImplicitDef && OtherV.Resolution == CR_Keep; + bool EraseImpDef = OtherV.ErasableImplicitDef && + OtherV.Resolution == CR_Keep; if (!Def.isBlock()) { // Remove <def,read-undef> flags. This def is now a partial redef. // Also remove <def,dead> flags since the joined live range will @@ -1843,7 +1872,7 @@ void JoinVals::eraseInstrs(SmallPtrSet<MachineInstr*, 8> &ErasedInstrs, // If an IMPLICIT_DEF value is pruned, it doesn't serve a purpose any // longer. The IMPLICIT_DEF instructions are only inserted by // PHIElimination to guarantee that all PHI predecessors have a value. - if (!Vals[i].IsImplicitDef || !Vals[i].Pruned) + if (!Vals[i].ErasableImplicitDef || !Vals[i].Pruned) break; // Remove value number i from LI. Note that this VNInfo is still present // in NewVNInfo, so it will appear as an unused value number in the final |