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Fix PR3149. If an early clobber def is a physical register and it is tied to an input operand, it effectively extends the live range of the physical register. Currently we do not have a good way to represent this.

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172     %ECX<def> = MOV32rr %reg1039<kill>
180     INLINEASM <es:subl $5,$1
        sbbl $3,$0>, 10, %EAX<def>, 14, %ECX<earlyclobber,def>, 9, %EAX<kill>,
36, <fi#0>, 1, %reg0, 0, 9, %ECX<kill>, 36, <fi#1>, 1, %reg0, 0
188     %EAX<def> = MOV32rr %EAX<kill>
196     %ECX<def> = MOV32rr %ECX<kill>
204     %ECX<def> = MOV32rr %ECX<kill>
212     %EAX<def> = MOV32rr %EAX<kill>
220     %EAX<def> = MOV32rr %EAX
228     %reg1039<def> = MOV32rr %ECX<kill>

The early clobber operand ties ECX input to the ECX def.

The live interval of ECX is represented as this:
%reg20,inf = [46,47:1)[174,230:0)  0@174-(230) 1@46-(47)

The right way to represent this is something like
%reg20,inf = [46,47:2)[174,182:1)[181:230:0)  0@174-(182) 1@181-230 @2@46-(47)

Of course that won't work since that means overlapping live ranges defined by two val#.

The workaround for now is to add a bit to val# which says the val# is redefined by a early clobber def somewhere. This prevents the move at 228 from being optimized away by SimpleRegisterCoalescing::AdjustCopiesBackFrom.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@61259 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Evan Cheng
2008-12-19 20:58:01 +00:00
parent de8c611c08
commit 5379f412bc
5 changed files with 69 additions and 11 deletions
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16
lib/CodeGen/LiveIntervalAnalysis.cpp
View File

@@ -360,6 +360,7 @@ void LiveIntervals::handleVirtualRegisterDef(MachineBasicBlock *mbb,
mi->getOpcode() == TargetInstrInfo::INSERT_SUBREG ||
tii_->isMoveInstr(*mi, SrcReg, DstReg))
CopyMI = mi;
// Earlyclobbers move back one.
ValNo = interval.getNextValue(defIndex, CopyMI, VNInfoAllocator);
assert(ValNo->id == 0 && "First value in interval is not 0?");
@@ -435,9 +436,8 @@ void LiveIntervals::handleVirtualRegisterDef(MachineBasicBlock *mbb,
assert(interval.containsOneValue());
unsigned DefIndex = getDefIndex(interval.getValNumInfo(0)->def);
unsigned RedefIndex = getDefIndex(MIIdx);
// Earlyclobbers move back one.
if (MO.isEarlyClobber())
RedefIndex = getUseIndex(MIIdx);
// It cannot be an early clobber MO.
assert(!MO.isEarlyClobber() && "Unexpected early clobber!");
const LiveRange *OldLR = interval.getLiveRangeContaining(RedefIndex-1);
VNInfo *OldValNo = OldLR->valno;
@@ -505,9 +505,8 @@ void LiveIntervals::handleVirtualRegisterDef(MachineBasicBlock *mbb,
// live until the end of the block. We've already taken care of the
// rest of the live range.
unsigned defIndex = getDefIndex(MIIdx);
// Earlyclobbers move back one.
if (MO.isEarlyClobber())
defIndex = getUseIndex(MIIdx);
// It cannot be an early clobber MO.
assert(!MO.isEarlyClobber() && "Unexpected early clobber!");
VNInfo *ValNo;
MachineInstr *CopyMI = NULL;
@@ -592,8 +591,11 @@ exit:
// Already exists? Extend old live interval.
LiveInterval::iterator OldLR = interval.FindLiveRangeContaining(start);
VNInfo *ValNo = (OldLR != interval.end())
bool Extend = OldLR != interval.end();
VNInfo *ValNo = Extend
? OldLR->valno : interval.getNextValue(start, CopyMI, VNInfoAllocator);
if (MO.isEarlyClobber() && Extend)
ValNo->redefByEC = true;
LiveRange LR(start, end, ValNo);
interval.addRange(LR);
interval.addKill(LR.valno, end);

20
lib/CodeGen/SimpleRegisterCoalescing.cpp
View File

@@ -119,6 +119,26 @@ bool SimpleRegisterCoalescing::AdjustCopiesBackFrom(LiveInterval &IntA,
if (ALR == IntA.end()) // Should never happen!
return false;
VNInfo *AValNo = ALR->valno;
// If it's re-defined by an early clobber somewhere in the live range, then
// it's not safe to eliminate the copy. FIXME: This is a temporary workaround.
// See PR3149:
// 172 %ECX<def> = MOV32rr %reg1039<kill>
// 180 INLINEASM <es:subl $5,$1
// sbbl $3,$0>, 10, %EAX<def>, 14, %ECX<earlyclobber,def>, 9, %EAX<kill>,
// 36, <fi#0>, 1, %reg0, 0, 9, %ECX<kill>, 36, <fi#1>, 1, %reg0, 0
// 188 %EAX<def> = MOV32rr %EAX<kill>
// 196 %ECX<def> = MOV32rr %ECX<kill>
// 204 %ECX<def> = MOV32rr %ECX<kill>
// 212 %EAX<def> = MOV32rr %EAX<kill>
// 220 %EAX<def> = MOV32rr %EAX
// 228 %reg1039<def> = MOV32rr %ECX<kill>
// The early clobber operand ties ECX input to the ECX def.
//
// The live interval of ECX is represented as this:
// %reg20,inf = [46,47:1)[174,230:0) 0@174-(230) 1@46-(47)
// The coalescer has no idea there was a def in the middle of [174,230].
if (AValNo->redefByEC)
return false;
// If AValNo is defined as a copy from IntB, we can potentially process this.
// Get the instruction that defines this value number.