[PATCH] D73301: [PatchableFunction] Allow empty entry MachineBasicBlock

[Fangrui Song via Phabricator via llvm-commits]

MaskRay created this revision.
MaskRay added reviewers: nickdesaulniers, peter.smith.
Herald added subscribers: llvm-commits, hiraditya.
Herald added a project: LLVM.

It is difficult to construct an IR test which will lower to an empty entry
MBB.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D73301

Files:
  llvm/lib/CodeGen/PatchableFunction.cpp


Index: llvm/lib/CodeGen/PatchableFunction.cpp
===================================================================
--- llvm/lib/CodeGen/PatchableFunction.cpp
+++ llvm/lib/CodeGen/PatchableFunction.cpp
@@ -57,10 +57,15 @@
 bool PatchableFunction::runOnMachineFunction(MachineFunction &MF) {
   if (MF.getFunction().hasFnAttribute("patchable-function-entry")) {
     MachineBasicBlock &FirstMBB = *MF.begin();
-    MachineInstr &FirstMI = *FirstMBB.begin();
     const TargetInstrInfo *TII = MF.getSubtarget().getInstrInfo();
-    BuildMI(FirstMBB, FirstMI, FirstMI.getDebugLoc(),
-            TII->get(TargetOpcode::PATCHABLE_FUNCTION_ENTER));
+    if (FirstMBB.empty()) {
+      BuildMI(&FirstMBB, DebugLoc(),
+              TII->get(TargetOpcode::PATCHABLE_FUNCTION_ENTER));
+    } else {
+      MachineInstr &FirstMI = *FirstMBB.begin();
+      BuildMI(FirstMBB, FirstMI, FirstMI.getDebugLoc(),
+              TII->get(TargetOpcode::PATCHABLE_FUNCTION_ENTER));
+    }
     return true;
   }
 


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