[MachineOutliner] Fix label outlining regression introduced in D125072

Due to a change in the APIs used to determine what instructions can be outlined, the check for label outling was never hit. Instead, all labels were considered invisible, which is the opposite of the intended behavior and causes obscure crashes down the line. We now replicate the original behavior more closely, with explicit checks for known-good and known-bad instruction types.

Reviewed by: paquette

Differential Revision: https://reviews.llvm.org/D147178

Author: duk-37

llvm/lib/CodeGen/TargetInstrInfo.cpp

@@ -1579,10 +1579,6 @@ outliner::InstrType TargetInstrInfo::getOutliningType(
     // Just go right to the target implementation.
     return getOutliningTypeImpl(MIT, Flags);
 
-  // Don't allow instructions that don't materialize to impact analysis.
-  if (MI.isMetaInstruction())
-    return outliner::InstrType::Invisible;
-
   // Be conservative about inline assembly.
   if (MI.isInlineAsm())
     return outliner::InstrType::Illegal;
@@ -1591,6 +1587,21 @@ outliner::InstrType TargetInstrInfo::getOutliningType(
   if (MI.isLabel())
     return outliner::InstrType::Illegal;
 
+  // Don't let debug instructions impact analysis.
+  if (MI.isDebugInstr())
+    return outliner::InstrType::Invisible;
+
+  // Some other special cases.
+  switch (MI.getOpcode()) {
+    case TargetOpcode::IMPLICIT_DEF:
+    case TargetOpcode::KILL:
+    case TargetOpcode::LIFETIME_START:
+    case TargetOpcode::LIFETIME_END:
+      return outliner::InstrType::Invisible;
+    default:
+      break;
+  }
+
   // Is this a terminator for a basic block?
   if (MI.isTerminator()) {
     // If this is a branch to another block, we can't outline it.

llvm/test/CodeGen/AArch64/machine-outliner-labels.mir

@@ -0,0 +1,49 @@
+# RUN: llc -mtriple aarch64 -run-pass=machine-outliner -verify-machineinstrs %s -o - | FileCheck %s
+# CHECK-NOT: OUTLINED_FUNCTION
+
+...
+---
+name:            foo1
+tracksRegLiveness: true
+machineFunctionInfo:
+  hasRedZone:      false
+body:             |
+  bb.0:
+    liveins: $x0
+    $x0 = ADDXri $x0, 0, 0
+    EH_LABEL <mcsymbol .Ltmp0>
+    EH_LABEL <mcsymbol .Ltmp1>
+    EH_LABEL <mcsymbol .Ltmp2>
+    EH_LABEL <mcsymbol .Ltmp3>
+    RET_ReallyLR implicit $x0
+...
+---
+name:            foo2
+tracksRegLiveness: true
+machineFunctionInfo:
+  hasRedZone:      false
+body:             |
+  bb.0:
+    liveins: $x0
+    $x0 = ADDXri $x0, 0, 0
+    EH_LABEL <mcsymbol .Ltmp0>
+    EH_LABEL <mcsymbol .Ltmp1>
+    EH_LABEL <mcsymbol .Ltmp2>
+    EH_LABEL <mcsymbol .Ltmp3>
+    RET_ReallyLR implicit $x0
+...
+---
+name:            foo3
+tracksRegLiveness: true
+machineFunctionInfo:
+  hasRedZone:      false
+body:             |
+  bb.0:
+    liveins: $x0
+    $x0 = ADDXri $x0, 0, 0
+    EH_LABEL <mcsymbol .Ltmp0>
+    EH_LABEL <mcsymbol .Ltmp1>
+    EH_LABEL <mcsymbol .Ltmp2>
+    EH_LABEL <mcsymbol .Ltmp3>
+    RET_ReallyLR implicit $x0
+...