[PATCH] D115360: [MachineVerifier] Undef subreg operands do not require subranges

[Jay Foad via Phabricator via llvm-commits]

foad created this revision.
foad added reviewers: arsenm, MatzeB, qcolombet, bjope.
Herald added subscribers: kerbowa, hiraditya, tpr, nhaehnle, jvesely.
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D112556 <https://reviews.llvm.org/D112556> added verification that the live interval for a subreg operand
must have subranges. This patch fixes a corner case, where if all subreg
operands for a particular register are marked as undef then no subranges
are required. This matches how LiveIntervalCalc would build the live
intervals in the first place, since an undef operand is not considered
to read the register.

Before this patch, CodeGen/AMDGPU/no-remat-indirect-mov.mir would fail
with -early-live-intervals:

1. After Live Interval Analysis

...

  - Bad machine code: Live interval for subreg operand has no subranges ***
- function:    index_vgpr_waterfall_loop
- basic block: %bb.1  (0x6a9a968) [352B;496B)
- instruction: 432B	%24:vgpr_32 = V_MOV_B32_e32 undef %18.sub0:vreg_512, implicit $exec, implicit %18:vreg_512, implicit $m0
- operand 1:   undef %18.sub0:vreg_512


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D115360

Files:
  llvm/lib/CodeGen/MachineVerifier.cpp
  llvm/test/CodeGen/AMDGPU/no-remat-indirect-mov.mir


Index: llvm/test/CodeGen/AMDGPU/no-remat-indirect-mov.mir
===================================================================
--- llvm/test/CodeGen/AMDGPU/no-remat-indirect-mov.mir
+++ llvm/test/CodeGen/AMDGPU/no-remat-indirect-mov.mir
@@ -1,5 +1,6 @@
 # NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
 # RUN: llc -mtriple=amdgcn-amd-amdhsa -mcpu=gfx900  -start-after=phi-node-elimination -stop-before=greedy -o - %s | FileCheck -check-prefix=GFX9 %s
+# RUN: llc -mtriple=amdgcn-amd-amdhsa -mcpu=gfx900  -start-after=phi-node-elimination -stop-before=greedy -early-live-intervals -o - %s | FileCheck -check-prefix=GFX9 %s
 
 # Make sure that the V_MOV_B32 isn't rematerialized out of the loop. This was also breaking RenameIndependentSubregisters which missed the use of all subregisters.
 
Index: llvm/lib/CodeGen/MachineVerifier.cpp
===================================================================
--- llvm/lib/CodeGen/MachineVerifier.cpp
+++ llvm/lib/CodeGen/MachineVerifier.cpp
@@ -2229,8 +2229,8 @@
   if (LiveInts && Reg.isVirtual()) {
     if (LiveInts->hasInterval(Reg)) {
       LI = &LiveInts->getInterval(Reg);
-      if (SubRegIdx != 0 && !LI->empty() && !LI->hasSubRanges() &&
-          MRI->shouldTrackSubRegLiveness(Reg))
+      if (SubRegIdx != 0 && !MO->isUndef() && !LI->empty() &&
+          !LI->hasSubRanges() && MRI->shouldTrackSubRegLiveness(Reg))
         report("Live interval for subreg operand has no subranges", MO, MONum);
     } else {
       report("Virtual register has no live interval", MO, MONum);


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