[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

diff --git a/llvm/lib/CodeGen/LiveIntervals.cpp b/llvm/lib/CodeGen/LiveIntervals.cpp
index a4dd71c..7bf21ac 100644 (file)
--- a/llvm/lib/CodeGen/LiveIntervals.cpp
+++ b/llvm/lib/CodeGen/LiveIntervals.cpp
@@ -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);
   }

diff --git a/llvm/test/CodeGen/AMDGPU/dead-lane.mir b/llvm/test/CodeGen/AMDGPU/dead-lane.mir
index 8e12265..a18e647 100644 (file)
--- a/llvm/test/CodeGen/AMDGPU/dead-lane.mir
+++ b/llvm/test/CodeGen/AMDGPU/dead-lane.mir
@@ -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:

diff --git a/llvm/test/CodeGen/Thumb2/mve-sext-masked-load.ll b/llvm/test/CodeGen/Thumb2/mve-sext-masked-load.ll
index bdf5fb2..7a62d6d 100644 (file)
--- a/llvm/test/CodeGen/Thumb2/mve-sext-masked-load.ll
+++ b/llvm/test/CodeGen/Thumb2/mve-sext-masked-load.ll
@@ -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: