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RegisterPressure: allocatable physreg uses are always kills

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This property was already used in the code path when no liveness
intervals are present. Unfortunately the code path that uses liveness
intervals tried to query a cached live interval for an allocatable
physreg, those are usually not computed so a conservative default was
used.

This doesn't affect any of the lit testcases. This is a foreclosure to
upcoming changes which should be NFC but without this patch this tidbit
wouldn't be NFC.

llvm-svn: 250596
This commit is contained in:
Matthias Braun 2015-10-17 00:46:57 +00:00
parent 24b9e3b760
commit 894abcd9d3
2 changed files with 29 additions and 25 deletions
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2
include/llvm/CodeGen/RegisterPressure.h
View File

@ -418,6 +418,8 @@ public:
protected:
const LiveRange *getLiveRange(unsigned Reg) const;
bool isLastUse(unsigned VRegOrUnit, SlotIndex Pos) const;
void increaseRegPressure(ArrayRef<unsigned> Regs);
void decreaseRegPressure(ArrayRef<unsigned> Regs);

52
lib/CodeGen/RegisterPressure.cpp
View File

@ -561,6 +561,17 @@ bool RegPressureTracker::recede(SmallVectorImpl<unsigned> *LiveUses,
return true;
}
bool RegPressureTracker::isLastUse(unsigned VRegOrUnit, SlotIndex Pos) const {
// Allocatable physregs are always single-use before register rewriting.
if (!TargetRegisterInfo::isVirtualRegister(VRegOrUnit))
return true;
// Without liveness information we conservatively assume "no last use".
if (!RequireIntervals)
return false;
const LiveRange *LR = getLiveRange(VRegOrUnit);
return LR && LR->Query(Pos).isKill();
}
/// Advance across the current instruction.
bool RegPressureTracker::advance() {
assert(!TrackUntiedDefs && "unsupported mode");
@ -595,21 +606,15 @@ bool RegPressureTracker::advance() {
if (!isLive)
discoverLiveIn(Reg);
// Kill liveness at last uses.
bool lastUse = false;
if (RequireIntervals) {
const LiveRange *LR = getLiveRange(Reg);
lastUse = LR && LR->Query(SlotIdx).isKill();
}
else {
// Allocatable physregs are always single-use before register rewriting.
lastUse = !TargetRegisterInfo::isVirtualRegister(Reg);
}
if (lastUse && isLive) {
LiveRegs.erase(Reg);
decreaseRegPressure(Reg);
}
else if (!lastUse && !isLive)
if (isLastUse(Reg, SlotIdx)) {
if (isLive) {
LiveRegs.erase(Reg);
decreaseRegPressure(Reg);
}
} else if(!isLive) {
// We discovered a live which was not last used here, adjust pressure.
increaseRegPressure(Reg);
}
}
// Generate liveness for defs.
@ -924,21 +929,18 @@ void RegPressureTracker::bumpDownwardPressure(const MachineInstr *MI) {
for (unsigned i = 0, e = RegOpers.Uses.size(); i < e; ++i) {
unsigned Reg = RegOpers.Uses[i];
if (RequireIntervals) {
bool IsLastUse = isLastUse(Reg, SlotIdx);
// We had a last use at MIs position. To know the situation for the current
// position we have to check if there exist other uses in between.
if (IsLastUse && TargetRegisterInfo::isVirtualRegister(Reg)) {
SlotIndex CurrIdx = getCurrSlot();
// FIXME: allow the caller to pass in the list of vreg uses that remain
// to be bottom-scheduled to avoid searching uses at each query.
SlotIndex CurrIdx = getCurrSlot();
const LiveRange *LR = getLiveRange(Reg);
if (LR) {
LiveQueryResult LRQ = LR->Query(SlotIdx);
if (LRQ.isKill() && !findUseBetween(Reg, CurrIdx, SlotIdx, *MRI, LIS))
decreaseRegPressure(Reg);
}
if (findUseBetween(Reg, CurrIdx, SlotIdx, *MRI, LIS))
IsLastUse = false;
}
else if (!TargetRegisterInfo::isVirtualRegister(Reg)) {
// Allocatable physregs are always single-use before register rewriting.
if (IsLastUse)
decreaseRegPressure(Reg);
}
}
// Generate liveness for defs.