[PatchableFunction] Allow empty entry MachineBasicBlock

MaskRay · MaskRay · commit 50a3ff30e158 · 2020-01-24T09:42:48.000-08:00
Reviewed By: nickdesaulniers Differential Revision: https://reviews.llvm.org/D73301
diff --git a/llvm/lib/CodeGen/PatchableFunction.cpp b/llvm/lib/CodeGen/PatchableFunction.cpp
@@ -57,10 +57,15 @@ static bool doesNotGeneratecode(const MachineInstr &MI) {
 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;
   }
 
diff --git a/llvm/test/CodeGen/AArch64/patchable-function-entry-empty.mir b/llvm/test/CodeGen/AArch64/patchable-function-entry-empty.mir
@@ -0,0 +1,64 @@
+# RUN: llc -mtriple=aarch64 -run-pass=patchable-function %s -o - | FileCheck %s
+
+# CHECK:    name: empty
+# CHECK:    bb.0.entry
+# CHECK:      PATCHABLE_FUNCTION_ENTER debug-location !DILocation(line: 1,
+# CHECK-NEXT: RET undef $lr, debug-location !DILocation(line: 1,
+
+## Empty entry MBB, no debug location.
+# CHECK:    name: empty_entry
+# CHECK:    bb.0.entry
+# CHECK:      PATCHABLE_FUNCTION_ENTER{{$}}
+# CHECK:    bb.1.here
+
+--- |
+  define void @empty() #0 !dbg !7 {
+  entry:
+    ret void, !dbg !10
+  }
+
+  define void @empty_entry() #0 !dbg !11 {
+  entry:
+    br label %here
+  here:
+    ret void, !dbg !12
+  }
+
+  attributes #0 = { "patchable-function-entry"="1" }
+  !0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 11.0.0 ", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, splitDebugInlining: false, nameTableKind: None)
+  !1 = !DIFile(filename: "a.c", directory: "/tmp")
+  !2 = !{}
+  !3 = !{i32 7, !"Dwarf Version", i32 4}
+  !4 = !{i32 2, !"Debug Info Version", i32 3}
+  !5 = !{i32 1, !"wchar_size", i32 4}
+  !6 = !{!"clang version 11.0.0 "}
+  !7 = distinct !DISubprogram(name: "empty", scope: !1, file: !1, line: 1, type: !8, scopeLine: 1, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2)
+  !8 = !DISubroutineType(types: !9)
+  !9 = !{null}
+  !10 = !DILocation(line: 1, column: 61, scope: !7)
+  !11 = distinct !DISubprogram(name: "empty_entry", scope: !1, file: !1, line: 2, type: !8, scopeLine: 2, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2)
+  !12 = !DILocation(line: 2, column: 61, scope: !11)
+
+...
+---
+name:            empty
+alignment:       4
+tracksRegLiveness: true
+body:             |
+  bb.0.entry:
+    liveins: $lr
+    RET undef $lr, debug-location !10
+
+...
+---
+name:            empty_entry
+alignment:       4
+tracksRegLiveness: true
+body:             |
+  bb.0.entry:
+    liveins: $lr
+  bb.1.here:
+    liveins: $lr
+    RET undef $lr, debug-location !12
+
+...
