[LiveRange] Fix inaccurate verification of live-in PhysRegs

[critson]

Summary

Fix verification that a PhysReg is live in to an MBB.
isLiveIn does not handle reg units, so cannot identify when a
register would be defined because its super register is partially
defined.
Additionally a PhysReg may be partial defined at block entry and
then fully defined before any use.

[foad]

Could you still check that at least one aliasing registers is in the liveins? (Much as I am loath to suggest new uses of MCRegAliasIterator.)

Do you have a test case? Does it only show up before PHIElimination, and if so why?

[critson]

In D157086#4560602, @foad wrote:

Could you still check that at least one aliasing registers is in the liveins? (Much as I am loath to suggest new uses of MCRegAliasIterator.)

Yes, we can check aliases -- this is only compiled with debug and so it's probably acceptable.

Do you have a test case? Does it only show up before PHIElimination, and if so why?

This happens during / post-RA; however, normally we do not generate/regenerate LiveIntervals at this point hence this is an edge case.

[critson]

• Rework to check aliases instead of removing check entirely
• Add test cases

[foad]

Seems reasonable. I wonder if you could get an IR test with llc -early-live-intervals.

llvm/lib/CodeGen/LiveRangeCalc.cpp

223

This looks like a job for /*IncludeSelf=*/true, but I guess it wouldn't actually shorten the code much the way you've written it.

llvm/lib/CodeGen/LiveRangeCalc.cpp

if (MBB->pred_empty()) {
       errs() << "Use of " << printReg(PhysReg, MRI->getTargetRegisterInfo())
              << " does not have a corresponding definition on every path:\n";
       const MachineInstr *MI = Indexes->getInstructionFromIndex(Use);
       if (MI != nullptr)
         errs() << Use << " " << *MI;
       report_fatal_error("Use not jointly dominated by defs.");
     }
 
-    if (Register::isPhysicalRegister(PhysReg) && !MBB->isLiveIn(PhysReg)) {
-      MBB->getParent()->verify();
+    if (Register::isPhysicalRegister(PhysReg)) {
       const TargetRegisterInfo *TRI = MRI->getTargetRegisterInfo();
+      bool IsLiveIn = MBB->isLiveIn(PhysReg);
+      for (MCRegAliasIterator Alias(PhysReg, TRI, false); !IsLiveIn && Alias.isValid(); ++Alias)
+        IsLiveIn = MBB->isLiveIn(*Alias);
+      if (!IsLiveIn) {
+        MBB->getParent()->verify();
         errs() << "The register " << printReg(PhysReg, TRI)
                << " needs to be live in to " << printMBBReference(*MBB)
                << ", but is missing from the live-in list.\n";
         report_fatal_error("Invalid global physical register");
       }
+    }
 #endif
     FoundUndef |= MBB->pred_empty();
 
     for (MachineBasicBlock *Pred : MBB->predecessors()) {
        // Is this a known live-out block?
        if (Seen.test(Pred->getNumber())) {
          if (VNInfo *VNI = Map[Pred].first) {
            if (TheVNI && TheVNI != VNI)

llvm/test/CodeGen/AMDGPU/phys-partial-liveness.mir

+# RUN: llc -mtriple=amdgcn--amdpal -mcpu=gfx1100 -debug-only=regalloc -verify-machineinstrs -run-pass=liveintervals -o - %s 2>&1 | FileCheck %s
+# REQUIRES: asserts
+
+# CHECK: Computing live-in reg-units in ABI blocks.
+# CHECK: 0B      %bb.0 SGPR16_LO16#0 SGPR16_HI16#0
+# CHECK: SGPR16_LO16 [0B,16r:0)[32r,144r:1) 0@0B-phi 1@32r
+# CHECK: SGPR16_HI16 [0B,16r:0)[32r,144r:1) 0@0B-phi 1@32r
+
+# CHECK: Computing live-in reg-units in ABI blocks.
+# CHECK: 0B      %bb.0 SGPR2_LO16#0 SGPR2_HI16#0 SGPR3_LO16#0 SGPR3_HI16#0 SGPR7_LO16#0 SGPR7_HI16#0
+# CHECK: SGPR2_LO16 [0B,64r:0) 0@0B-phi
+# CHECK: SGPR2_HI16 [0B,64r:0) 0@0B-phi
+# CHECK: SGPR3_LO16 [0B,16r:0)[48r,64r:1) 0@0B-phi 1@48r
+# CHECK: SGPR3_HI16 [0B,16r:0)[48r,64r:1) 0@0B-phi 1@48r
+# CHECK: SGPR7_LO16 [0B,48r:0) 0@0B-phi
+# CHECK: SGPR7_HI16 [0B,48r:0) 0@0B-phi
+
+---
+name: phys_reg_partial_liveness_1
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    successors: %bb.1
+    liveins: $sgpr16
+
+    $sgpr1 = S_AND_B32 3, killed $sgpr16, implicit-def $scc
+    $sgpr16 = S_AND_B32 2, killed $sgpr1, implicit-def $scc
+
+  bb.1:
+    successors: %bb.2
+    liveins: $sgpr16_sgpr17_sgpr18_sgpr19:0x0000000000000003
+
+    $sgpr18 = S_MOV_B32 -1
+    $sgpr17 = S_MOV_B32 -2097152000
+    $sgpr19 = S_MOV_B32 -2122316801
+    renamable $sgpr42 = COPY renamable $sgpr16
+
+  bb.2:
+    liveins: $sgpr16_sgpr17_sgpr18_sgpr19:0x00000000000000FF, $sgpr42
+
+    $sgpr2 = S_BUFFER_LOAD_DWORD_IMM $sgpr16_sgpr17_sgpr18_sgpr19, 3780, 0 :: (dereferenceable invariant load (s32))
+    $sgpr0 = S_AND_B32 $sgpr42, $sgpr2, implicit-def $scc
+    S_ENDPGM 0, implicit $sgpr0
+...
+
+---
+name: phys_reg_partial_liveness_2
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    successors: %bb.1
+    liveins: $sgpr2, $sgpr3, $sgpr7
+
+    $sgpr1 = S_AND_B32 1, killed $sgpr3, implicit-def $scc
+
+  bb.1:
+    successors: %bb.2
+    liveins: $sgpr2_sgpr3:0x0000000000000003, $sgpr7
+
+    $sgpr3 = COPY $sgpr7
+    $sgpr0 = S_LOAD_DWORD_IMM $sgpr2_sgpr3, 0, 0 :: (dereferenceable invariant load (s32))
+
+  bb.2:
+    liveins: $sgpr0
+
+    S_ENDPGM 0, implicit $sgpr0
+...
+