/// isWinToJoinCrossClass - Return true if it's profitable to coalesce
/// two virtual registers from different register classes.
bool
-SimpleRegisterCoalescing::isWinToJoinCrossClass(unsigned LargeReg,
- unsigned SmallReg,
- unsigned Threshold) {
- // Then make sure the intervals are *short*.
- LiveInterval &LargeInt = li_->getInterval(LargeReg);
- LiveInterval &SmallInt = li_->getInterval(SmallReg);
- unsigned LargeSize = li_->getApproximateInstructionCount(LargeInt);
- unsigned SmallSize = li_->getApproximateInstructionCount(SmallInt);
- if (LargeSize > Threshold) {
- unsigned SmallUses = std::distance(mri_->use_nodbg_begin(SmallReg),
- mri_->use_nodbg_end());
- unsigned LargeUses = std::distance(mri_->use_nodbg_begin(LargeReg),
- mri_->use_nodbg_end());
- if (SmallUses*LargeSize < LargeUses*SmallSize)
+SimpleRegisterCoalescing::isWinToJoinCrossClass(unsigned SrcReg,
+ unsigned DstReg,
+ const TargetRegisterClass *SrcRC,
+ const TargetRegisterClass *DstRC,
+ const TargetRegisterClass *NewRC) {
+ unsigned NewRCCount = allocatableRCRegs_[NewRC].count();
+ // This heuristics is good enough in practice, but it's obviously not *right*.
+ // 4 is a magic number that works well enough for x86, ARM, etc. It filter
+ // out all but the most restrictive register classes.
+ if (NewRCCount > 4 ||
+ // Early exit if the function is fairly small, coalesce aggressively if
+ // that's the case. For really special register classes with 3 or
+ // fewer registers, be a bit more careful.
+ (li_->getFuncInstructionCount() / NewRCCount) < 8)
+ return true;
+ LiveInterval &SrcInt = li_->getInterval(SrcReg);
+ LiveInterval &DstInt = li_->getInterval(DstReg);
+ unsigned SrcSize = li_->getApproximateInstructionCount(SrcInt);
+ unsigned DstSize = li_->getApproximateInstructionCount(DstInt);
+ if (SrcSize <= NewRCCount && DstSize <= NewRCCount)
+ return true;
+ // Estimate *register use density*. If it doubles or more, abort.
+ unsigned SrcUses = std::distance(mri_->use_nodbg_begin(SrcReg),
+ mri_->use_nodbg_end());
+ unsigned DstUses = std::distance(mri_->use_nodbg_begin(DstReg),
+ mri_->use_nodbg_end());
+ float NewDensity = ((float)(SrcUses + DstUses) / (SrcSize + DstSize)) /
+ NewRCCount;
+ if (SrcRC != NewRC && SrcSize > NewRCCount) {
+ unsigned SrcRCCount = allocatableRCRegs_[SrcRC].count();
+ float Density = ((float)SrcUses / SrcSize) / SrcRCCount;
+ if (NewDensity > Density * 2.0f)
+ return false;
+ }
+ if (DstRC != NewRC && DstSize > NewRCCount) {
+ unsigned DstRCCount = allocatableRCRegs_[DstRC].count();
+ float Density = ((float)DstUses / DstSize) / DstRCCount;
+ if (NewDensity > Density * 2.0f)
return false;
}
return true;
return false; // Not coalescable
}
- unsigned LargeReg = isExtSubReg ? SrcReg : DstReg;
- unsigned SmallReg = isExtSubReg ? DstReg : SrcReg;
- unsigned Limit= allocatableRCRegs_[mri_->getRegClass(SmallReg)].count();
- if (!isWinToJoinCrossClass(LargeReg, SmallReg, Limit)) {
+ if (!isWinToJoinCrossClass(SrcReg, DstReg, SrcRC, DstRC, NewRC)) {
+ DEBUG(dbgs() << "\tAvoid coalescing to constrainted register class: "
+ << SrcRC->getName() << "/"
+ << DstRC->getName() << " -> "
+ << NewRC->getName() << ".\n");
Again = true; // May be possible to coalesce later.
return false;
}
}
}
- unsigned LargeReg = SrcReg;
- unsigned SmallReg = DstReg;
-
// Now determine the register class of the joined register.
- if (isExtSubReg) {
- if (SubIdx && DstRC && DstRC->isASubClass()) {
- // This is a move to a sub-register class. However, the source is a
- // sub-register of a larger register class. We don't know what should
- // the register class be. FIXME.
- Again = true;
- return false;
+ if (!SrcIsPhys && !DstIsPhys) {
+ if (isExtSubReg) {
+ NewRC =
+ SubIdx ? tri_->getMatchingSuperRegClass(SrcRC, DstRC, SubIdx) : SrcRC;
+ } else if (isInsSubReg) {
+ NewRC =
+ SubIdx ? tri_->getMatchingSuperRegClass(DstRC, SrcRC, SubIdx) : DstRC;
+ } else {
+ NewRC = getCommonSubClass(SrcRC, DstRC);
}
- if (!DstIsPhys && !SrcIsPhys)
- NewRC = SrcRC;
- } else if (!SrcIsPhys && !DstIsPhys) {
- NewRC = getCommonSubClass(SrcRC, DstRC);
+
if (!NewRC) {
DEBUG(dbgs() << "\tDisjoint regclasses: "
<< SrcRC->getName() << ", "
<< DstRC->getName() << ".\n");
return false; // Not coalescable.
}
- if (DstRC->getSize() > SrcRC->getSize())
- std::swap(LargeReg, SmallReg);
- }
- // If we are joining two virtual registers and the resulting register
- // class is more restrictive (fewer register, smaller size). Check if it's
- // worth doing the merge.
- if (!SrcIsPhys && !DstIsPhys &&
- (isExtSubReg || DstRC->isASubClass()) &&
- !isWinToJoinCrossClass(LargeReg, SmallReg,
- allocatableRCRegs_[NewRC].count())) {
- DEBUG(dbgs() << "\tSrc/Dest are different register classes: "
- << SrcRC->getName() << "/"
- << DstRC->getName() << " -> "
- << NewRC->getName() << ".\n");
- // Allow the coalescer to try again in case either side gets coalesced to
- // a physical register that's compatible with the other side. e.g.
- // r1024 = MOV32to32_ r1025
- // But later r1024 is assigned EAX then r1025 may be coalesced with EAX.
- Again = true; // May be possible to coalesce later.
- return false;
+ // If we are joining two virtual registers and the resulting register
+ // class is more restrictive (fewer register, smaller size). Check if it's
+ // worth doing the merge.
+ if (!isWinToJoinCrossClass(SrcReg, DstReg, SrcRC, DstRC, NewRC)) {
+ DEBUG(dbgs() << "\tAvoid coalescing to constrainted register class: "
+ << SrcRC->getName() << "/"
+ << DstRC->getName() << " -> "
+ << NewRC->getName() << ".\n");
+ // Allow the coalescer to try again in case either side gets coalesced to
+ // a physical register that's compatible with the other side. e.g.
+ // r1024 = MOV32to32_ r1025
+ // But later r1024 is assigned EAX then r1025 may be coalesced with EAX.
+ Again = true; // May be possible to coalesce later.
+ return false;
+ }
}
}
projects / oota-llvm.git / blobdiff