[RA] Don't split a register generated from another split

llvm/lib/CodeGen/RegAllocGreedy.cpp

@@ -1218,6 +1218,10 @@ bool RAGreedy::trySplitAroundHintReg(MCPhysReg Hint,
                                      const LiveInterval &VirtReg,
                                      SmallVectorImpl<Register> &NewVRegs,
                                      AllocationOrder &Order) {
+  // Don't allow repeated splitting as a safe guard against looping.
+  if (ExtraInfo->getStage(VirtReg) >= RS_Split2)
+    return false;
+
   BlockFrequency Cost = 0;
   Register Reg = VirtReg.reg();
 

llvm/test/CodeGen/ARM/split-deadloop.mir

@@ -0,0 +1,111 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 3
+# RUN: llc -o - %s -run-pass=greedy | FileCheck %s
+#
+# Make sure we don't run into dead loop when split register with a hint.
+
+--- |
+  target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
+  target triple = "aarch64-none-linux-gnu"
+
+  define void @foo(ptr %0, i32 %1) gc "statepoint-example" personality ptr null {
+  bci_0:
+    unreachable
+
+  bci_19:
+    unreachable
+
+  bci_10:
+    unreachable
+  }
+
+...
+---
+name:            foo
+alignment:       4
+exposesReturnsTwice: false
+legalized:       false
+regBankSelected: false
+selected:        false
+failedISel:      false
+tracksRegLiveness: true
+hasWinCFI:       false
+callsEHReturn:   false
+callsUnwindInit: false
+hasEHCatchret:   false
+hasEHScopes:     false
+hasEHFunclets:   false
+isOutlined:      false
+debugInstrRef:   false
+failsVerification: false
+tracksDebugUserValues: false
+registers:
+  - { id: 0, class: gpr64, preferred-register: '' }
+  - { id: 1, class: gpr32, preferred-register: '' }
+  - { id: 2, class: gpr32, preferred-register: '' }
+  - { id: 3, class: gpr64all, preferred-register: '' }
+  - { id: 4, class: gpr64all, preferred-register: '' }
+  - { id: 5, class: gpr32all, preferred-register: '' }
+liveins:
+  - { reg: '$w1', virtual-reg: '%1' }
+frameInfo:
+  isFrameAddressTaken: false
+  isReturnAddressTaken: false
+  hasStackMap:     false
+  hasPatchPoint:   false
+  stackSize:       0
+  offsetAdjustment: 0
+  maxAlignment:    1
+  adjustsStack:    true
+  hasCalls:        true
+  stackProtector:  ''
+  functionContext: ''
+  maxCallFrameSize: 0
+  cvBytesOfCalleeSavedRegisters: 0
+  hasOpaqueSPAdjustment: false
+  hasVAStart:      false
+  hasMustTailInVarArgFunc: false
+  hasTailCall:     false
+  localFrameSize:  0
+  savePoint:       ''
+  restorePoint:    ''
+fixedStack:      []
+stack:           []
+entry_values:    []
+callSites:       []
+debugValueSubstitutions: []
+constants:       []
+machineFunctionInfo: {}
+body:             |
+  ; CHECK-LABEL: name: foo
+  ; CHECK: bb.0.bci_0:
+  ; CHECK-NEXT:   successors: %bb.1(0x80000000)
+  ; CHECK-NEXT:   liveins: $w1
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT:   [[COPY:%[0-9]+]]:gpr32 = COPY $w1
+  ; CHECK-NEXT: {{  $}}
+  ; CHECK-NEXT: bb.1.bci_19:
+  ; CHECK-NEXT:   ADJCALLSTACKDOWN 0, 0, implicit-def dead $sp, implicit $sp
+  ; CHECK-NEXT:   $x0 = COPY $xzr
+  ; CHECK-NEXT:   STATEPOINT 0, 0, 1, $xzr, killed $x0, 2, 0, 2, 0, 2, 33, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, [[COPY]], 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 1, 2, 0, 2, 0, 2, 1, 0, 0, csr_aarch64_aapcs, implicit-def $sp, implicit-def dead $x0, implicit-def dead early-clobber $lr
+  ; CHECK-NEXT:   ADJCALLSTACKUP 0, 0, implicit-def dead $sp, implicit $sp
+  ; CHECK-NEXT:   ADJCALLSTACKDOWN 0, 0, implicit-def dead $sp, implicit $sp
+  ; CHECK-NEXT:   $w0 = COPY $wzr
+  ; CHECK-NEXT:   STATEPOINT 0, 0, 1, $xzr, killed $w0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, csr_aarch64_aapcs, implicit-def $sp, implicit-def dead early-clobber $lr
+  ; CHECK-NEXT:   ADJCALLSTACKUP 0, 0, implicit-def dead $sp, implicit $sp
+  bb.0.bci_0:
+    successors: %bb.1(0x80000000)
+    liveins: $w1
+
+    %1:gpr32 = COPY $w1
+
+  bb.1.bci_19:
+    ADJCALLSTACKDOWN 0, 0, implicit-def dead $sp, implicit $sp
+    $x0 = COPY $xzr
+    STATEPOINT 0, 0, 1, $xzr, killed $x0, 2, 0, 2, 0, 2, 33, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, %1, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 1, 2, 0, 2, 0, 2, 1, 0, 0, csr_aarch64_aapcs, implicit-def $sp, implicit-def dead $x0, implicit-def dead early-clobber $lr
+    ADJCALLSTACKUP 0, 0, implicit-def dead $sp, implicit $sp
+    ADJCALLSTACKDOWN 0, 0, implicit-def dead $sp, implicit $sp
+    $w0 = COPY $wzr
+    STATEPOINT 0, 0, 1, $xzr, killed $w0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, 2, 0, csr_aarch64_aapcs, implicit-def $sp, implicit-def dead early-clobber $lr
+    ADJCALLSTACKUP 0, 0, implicit-def dead $sp, implicit $sp
+
+...