[llvm] r279637 - [Hexagon] Remove the utilization of IMPLICIT_DEFs from expand-condsets
Krzysztof Parzyszek via llvm-commits
llvm-commits at lists.llvm.org
Wed Aug 24 09:36:37 PDT 2016
Author: kparzysz
Date: Wed Aug 24 11:36:37 2016
New Revision: 279637
URL: http://llvm.org/viewvc/llvm-project?rev=279637&view=rev
Log:
[Hexagon] Remove the utilization of IMPLICIT_DEFs from expand-condsets
This is no longer necessary, because since r279625 the subregister
liveness properly accounts for read-undefs.
Modified:
llvm/trunk/lib/Target/Hexagon/HexagonExpandCondsets.cpp
Modified: llvm/trunk/lib/Target/Hexagon/HexagonExpandCondsets.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/Hexagon/HexagonExpandCondsets.cpp?rev=279637&r1=279636&r2=279637&view=diff
==============================================================================
--- llvm/trunk/lib/Target/Hexagon/HexagonExpandCondsets.cpp (original)
+++ llvm/trunk/lib/Target/Hexagon/HexagonExpandCondsets.cpp Wed Aug 24 11:36:37 2016
@@ -85,58 +85,6 @@
// implicit uses will be added later, after predication. The extra price,
// however, is that finding the locations where the implicit uses need
// to be added, and updating the live ranges will be more involved.
-//
-// An additional problem appears when subregister liveness tracking is
-// enabled. In such a scenario, the live interval for the super-register
-// will have live ranges for each subregister (i.e. subranges). This sub-
-// range contains all liveness information about the subregister, except
-// for one case: a "read-undef" flag from another subregister will not
-// be reflected: given
-// vreg1:subreg_hireg<def,read-undef> = ... ; "undefines" subreg_loreg
-// the subrange for subreg_loreg will not have any indication that it is
-// undefined at this point. Calculating subregister liveness based only
-// on the information from the subrange may create a segment which spans
-// over such a "read-undef" flag. This would create inconsistencies in
-// the liveness data, resulting in assertions or incorrect code.
-// Example:
-// vreg1:subreg_loreg<def> = ...
-// vreg1:subreg_hireg<def, read-undef> = ... ; "undefines" subreg_loreg
-// ...
-// vreg1:subreg_loreg<def> = A2_tfrt ... ; may end up with imp-use
-// ; of subreg_loreg
-// The remedy takes advantage of the fact, that at this point we have
-// an unconditional definition of the subregister. What this means is
-// that any preceding value in this subregister will be overwritten,
-// or in other words, the last use before this def is a kill. This also
-// implies that the first of the predicated transfers at this location
-// should not have any implicit uses.
-// Assume for a moment that no part of the corresponding super-register
-// is used as a source. In such case, the entire super-register can be
-// considered undefined immediately before this instruction. Because of
-// that, we can insert an IMPLICIT_DEF of the super-register at this
-// location, which will cause it to be reflected in all the associated
-// subranges. What is important here is that if an IMPLICIT_DEF of
-// subreg_loreg was used, we would lose the indication that subreg_hireg
-// is also considered undefined. This could lead to having implicit uses
-// incorrectly added.
-//
-// What is left is the two cases when the super-register is used as a
-// source.
-// * Case 1: the used part is the same as the one that is defined:
-// vreg1<def> = ...
-// ...
-// vreg1:subreg_loreg<def,read-undef> = C2_mux ..., vreg1:subreg_loreg
-// In the end, the subreg_loreg should be marked as live at the point of
-// the splitting:
-// vreg1:subreg_loreg<def,read-undef> = A2_tfrt ; should have imp-use
-// vreg1:subreg_loreg<def,read-undef> = A2_tfrf ; should have imp-use
-// Hence, an IMPLICIT_DEF of only vreg1:subreg_hireg would be sufficient.
-// * Case 2: the used part does not overlap the part being defined:
-// vreg1<def> = ...
-// ...
-// vreg1:subreg_loreg<def,read-undef> = C2_mux ..., vreg1:subreg_hireg
-// For this case, we insert an IMPLICIT_DEF of vreg1:subreg_hireg after
-// the C2_mux.
#define DEBUG_TYPE "expand-condsets"
@@ -207,7 +155,6 @@ namespace {
MachineDominatorTree *MDT;
MachineRegisterInfo *MRI;
LiveIntervals *LIS;
- std::set<MachineInstr*> LocalImpDefs;
bool CoaLimitActive, TfrLimitActive;
unsigned CoaLimit, TfrLimit, CoaCounter, TfrCounter;
@@ -236,7 +183,6 @@ namespace {
void addRefToMap(RegisterRef RR, ReferenceMap &Map, unsigned Exec);
bool isRefInMap(RegisterRef, ReferenceMap &Map, unsigned Exec);
- void removeImpDefSegments(LiveRange &Range);
void updateDeadsInRange(unsigned Reg, LaneBitmask LM, LiveRange &Range);
void updateKillFlags(unsigned Reg);
void updateDeadFlags(unsigned Reg);
@@ -393,14 +339,6 @@ void HexagonExpandCondsets::updateKillFl
}
-void HexagonExpandCondsets::removeImpDefSegments(LiveRange &Range) {
- auto StartImpDef = [this] (LiveRange::Segment &S) -> bool {
- return S.start.isRegister() &&
- LocalImpDefs.count(LIS->getInstructionFromIndex(S.start));
- };
- Range.segments.erase(remove_if(Range, StartImpDef), Range.end());
-}
-
void HexagonExpandCondsets::updateDeadsInRange(unsigned Reg, LaneBitmask LM,
LiveRange &Range) {
assert(TargetRegisterInfo::isVirtualRegister(Reg));
@@ -453,8 +391,6 @@ void HexagonExpandCondsets::updateDeadsI
if (!Seg.start.isRegister())
continue;
MachineInstr *DefI = LIS->getInstructionFromIndex(Seg.start);
- if (LocalImpDefs.count(DefI))
- continue;
Defs.insert(DefI->getParent());
if (HII->isPredicated(*DefI))
PredDefs.push_back(Seg.start);
@@ -494,8 +430,6 @@ void HexagonExpandCondsets::updateDeadsI
if (!Seg.start.isRegister())
continue;
MachineInstr *DefI = LIS->getInstructionFromIndex(Seg.start);
- if (LocalImpDefs.count(DefI))
- continue;
for (auto &Op : DefI->operands()) {
if (Seg.start.isDead() || !IsRegDef(Op))
continue;
@@ -504,12 +438,8 @@ void HexagonExpandCondsets::updateDeadsI
}
}
-
// Finally, add implicit uses to each predicated def that is reached
- // by other defs. Remove segments started by implicit-defs first, since
- // they do not define registers.
- removeImpDefSegments(Range);
-
+ // by other defs.
for (auto &Seg : Range) {
if (!Seg.start.isRegister() || !Range.liveAt(Seg.start.getPrevSlot()))
continue;
@@ -535,9 +465,6 @@ void HexagonExpandCondsets::updateDeadFl
for (LiveInterval::SubRange &S : LI.subranges()) {
updateDeadsInRange(Reg, S.LaneMask, S);
LIS->shrinkToUses(S, Reg);
- // LI::shrinkToUses will add segments started by implicit-defs.
- // Remove them again.
- removeImpDefSegments(S);
}
LI.clear();
LIS->constructMainRangeFromSubranges(LI);
@@ -654,37 +581,11 @@ bool HexagonExpandCondsets::split(Machin
<< MI);
MachineOperand &MD = MI.getOperand(0); // Definition
MachineOperand &MP = MI.getOperand(1); // Predicate register
- MachineOperand &MS1 = MI.getOperand(2); // Source value #1
- MachineOperand &MS2 = MI.getOperand(3); // Source value #2
assert(MD.isDef());
unsigned DR = MD.getReg(), DSR = MD.getSubReg();
bool ReadUndef = MD.isUndef();
MachineBasicBlock::iterator At = MI;
- if (ReadUndef && DSR != 0 && MRI->shouldTrackSubRegLiveness(DR)) {
- unsigned NewSR = 0;
- MachineBasicBlock::iterator DefAt = At;
- bool SameReg = (MS1.isReg() && DR == MS1.getReg()) ||
- (MS2.isReg() && DR == MS2.getReg());
- if (SameReg) {
- NewSR = (DSR == Hexagon::subreg_loreg) ? Hexagon::subreg_hireg
- : Hexagon::subreg_loreg;
- // Advance the insertion point if the subregisters differ between
- // the source and the target (with the same super-register).
- // Note: this case has never occured during tests.
- if ((MS1.isReg() && NewSR == MS1.getSubReg()) ||
- (MS2.isReg() && NewSR == MS2.getSubReg()))
- ++DefAt;
- }
- // Use "At", since "DefAt" may be end().
- MachineBasicBlock &B = *At->getParent();
- DebugLoc DL = At->getDebugLoc();
- auto ImpD = BuildMI(B, DefAt, DL, HII->get(TargetOpcode::IMPLICIT_DEF))
- .addReg(DR, RegState::Define, NewSR);
- LIS->InsertMachineInstrInMaps(*ImpD);
- LocalImpDefs.insert(&*ImpD);
- }
-
// First, create the two invididual conditional transfers, and add each
// of them to the live intervals information. Do that first and then remove
// the old instruction from live intervals.
@@ -1262,7 +1163,6 @@ bool HexagonExpandCondsets::runOnMachine
MDT = &getAnalysis<MachineDominatorTree>();
LIS = &getAnalysis<LiveIntervals>();
MRI = &MF.getRegInfo();
- LocalImpDefs.clear();
DEBUG(LIS->print(dbgs() << "Before expand-condsets\n",
MF.getFunction()->getParent()));
@@ -1298,9 +1198,6 @@ bool HexagonExpandCondsets::runOnMachine
std::inserter(Diff, Diff.begin()));
updateLiveness(Diff, false, false, true);
- for (auto *ImpD : LocalImpDefs)
- removeInstr(*ImpD);
-
DEBUG({
if (Changed)
LIS->print(dbgs() << "After expand-condsets\n",
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