[LiveIntervals] Remove unused subreg ranges in repairIntervalsInRange

If the old instructions mentioned a subreg that the new instructions do
not, remove the subrange for that subreg.

For example, in TwoAddressInstructionPass::eliminateRegSequence, if a
use operand in the REG_SEQUENCE has the undef flag then we don't
generate a copy for it so after the elimination there should be no live
interval at all for the corresponding subreg of the def.

This is a small step towards switching TwoAddressInstructionPass over
from LiveVariables to LiveIntervals. Currently this path is only tested
if you explicitly enable -early-live-intervals.

Differential Revision: https://reviews.llvm.org/D110542
This commit is contained in:
Jay Foad 2021-09-27 11:44:18 +01:00
parent 34d6c1822e
commit 156d7d2df7
3 changed files with 7 additions and 0 deletions

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@ -1655,6 +1655,10 @@ void LiveIntervals::repairOldRegInRange(const MachineBasicBlock::iterator Begin,
}
}
}
bool isStartValid = getInstructionFromIndex(LII->start);
if (!isStartValid && LII->end.isDead())
LR.removeSegment(*LII, true);
}
void
@ -1716,6 +1720,7 @@ LiveIntervals::repairIntervalsInRange(MachineBasicBlock *MBB,
for (LiveInterval::SubRange &S : LI.subranges())
repairOldRegInRange(Begin, End, EndIdx, S, Reg, S.LaneMask);
LI.removeEmptySubRanges();
repairOldRegInRange(Begin, End, EndIdx, LI, Reg);
}

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@ -1,4 +1,5 @@
# RUN: llc -march=amdgcn -mcpu=tonga %s -start-before detect-dead-lanes -stop-before machine-scheduler -verify-machineinstrs -o - | FileCheck -check-prefix=GCN %s
# RUN: llc -march=amdgcn -mcpu=tonga %s -start-before detect-dead-lanes -stop-before machine-scheduler -verify-machineinstrs -early-live-intervals -o - | FileCheck -check-prefix=GCN %s
# GCN-LABEL: name: dead_lane
# GCN: bb.0:

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@ -1,5 +1,6 @@
; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
; RUN: llc -mtriple=thumbv8.1m.main-none-none-eabi -mattr=+mve.fp,+fp64 -verify-machineinstrs -o - %s | FileCheck %s
; RUN: llc -mtriple=thumbv8.1m.main-none-none-eabi -mattr=+mve.fp,+fp64 -verify-machineinstrs -early-live-intervals -o - %s | FileCheck %s
define arm_aapcs_vfpcc <4 x float> @foo_v4i16(<4 x i16>* nocapture readonly %pSrc, i32 %blockSize, <4 x i16> %a) {
; CHECK-LABEL: foo_v4i16: