[LiveDebugValues] Terminate open ranges on DBG_VALUE $noreg

[jmorse]

Summary

In D68209, LiveDebugValues::transferDebugValue had a call to OpenRanges.erase shifted, and by accident this led to a code path where DBG_VALUEs of $noreg would not have their open range terminated, allowing variable locations to extend past blocks where they were terminated.

This patch correctly terminates the open range, if present, when such a DBG_VAUE is encountered, and add a test for this behaviour.

[vsk]

Thanks, lgtm!

llvm/test/DebugInfo/MIR/X86/livedebugvalues_loop_terminated.mir

6

nit, terminates

llvm/lib/CodeGen/LiveDebugValues.cpp

if (isDbgValueDescribedByReg(MI) || MI.getOperand(0).isImm() ||
     OpenRanges.erase(VL);
 
     LocIndex ID = VarLocIDs.insert(VL);
     // Add the VarLoc to OpenRanges from this DBG_VALUE.
     OpenRanges.insert(ID, VL);
   } else if (MI.hasOneMemOperand()) {
     llvm_unreachable("DBG_VALUE with mem operand encountered after regalloc?");
   } else {
-    // This must be an undefined location. We should leave OpenRanges closed.
+    // This must be an undefined location. If it has an open range, erase it.
     assert(MI.getOperand(0).isReg() && MI.getOperand(0).getReg() == 0 &&
            "Unexpected non-undef DBG_VALUE encountered");
+    VarLoc VL(MI, LS);
+    OpenRanges.erase(VL);
   }
 }
 
 /// Turn the entry value backup locations into primary locations.
 void LiveDebugValues::emitEntryValues(MachineInstr &MI,
                                       OpenRangesSet &OpenRanges,
                                       VarLocMap &VarLocIDs,
                                       TransferMap &Transfers,

llvm/test/DebugInfo/MIR/X86/livedebugvalues_loop_terminated.mir

+--- |
+  ; RUN: llc %s -march=x86-64 -run-pass=livedebugvalues -o - | FileCheck %s -implicit-check-not=DBG_VALUE
+
+  ; Check that DBG_VALUE instructions are not propagated into a loop that
+  ; explicitly terminates its location.
+
+  ; CHECK:       ![[VARNO:[0-9]+]] = !DILocalVariable(name: "myVar"
+  ; CHECK-LABEL: bb.0.entry:
+  ; CHECK:       DBG_VALUE $ebx, $noreg, ![[VARNO]], !DIExpression(),
+  ; CHECK-LABEL: bb.2.bb2:
+  ; CHECK:       DBG_VALUE $noreg, $noreg, ![[VARNO]], !DIExpression(),
+
+  define i32 @_Z8bb_to_bb() local_unnamed_addr !dbg !12 {
+  entry:
+    br label %bb1, !dbg !17
+  bb1:
+    br label %bb2, !dbg !17
+  bb2:
+    br label %bb3, !dbg !17
+  bb3:
+    ret i32 0, !dbg !17
+  }
+
+  !llvm.dbg.cu = !{!0}
+  !llvm.module.flags = !{!7, !8, !9, !10}
+  !llvm.ident = !{!11}
+  !0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 10.0.0)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, globals: !3, debugInfoForProfiling: true, nameTableKind: None)
+  !1 = !DIFile(filename: "main.cpp", directory: "F:\test")
+  !2 = !{}
+  !3 = !{!4}
+  !4 = !DIGlobalVariableExpression(var: !5, expr: !DIExpression())
+  !5 = distinct !DIGlobalVariable(name: "start", scope: !0, file: !1, line: 4, type: !6, isLocal: false, isDefinition: true)
+  !6 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+  !7 = !{i32 2, !"Dwarf Version", i32 4}
+  !8 = !{i32 2, !"Debug Info Version", i32 3}
+  !9 = !{i32 1, !"wchar_size", i32 2}
+  !10 = !{i32 7, !"PIC Level", i32 2}
+  !11 = !{!"clang version 10.0.0"}
+  !12 = distinct !DISubprogram(name: "bb_to_bb", linkageName: "bb_to_bb", scope: !1, file: !1, line: 6, type: !13, scopeLine: 6, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !15)
+  !13 = !DISubroutineType(types: !14)
+  !14 = !{!6, !6}
+  !15 = !{!16}
+  !16 = !DILocalVariable(name: "myVar", scope: !12, file: !1, line: 7, type: !6)
+  !17 = !DILocation(line: 10, scope: !12)
+
+...
+---
+name: _Z8bb_to_bb
+body:  |
+  bb.0.entry:
+    successors: %bb.1
+    $ebx = MOV32ri 0, debug-location !17
+    DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+
+  bb.1.bb1:
+    successors: %bb.2
+    $eax = MOV32ri 0, debug-location !17
+
+  bb.2.bb2:
+    successors: %bb.1, %bb.3
+    $ecx = MOV32ri 1, debug-location !17
+    DBG_VALUE $noreg, $noreg, !16, !DIExpression(), debug-location !17
+    JCC_1 %bb.1, 4, implicit killed $eflags
+
+  bb.3.bb3:
+    RETQ $eax, debug-location !17
+...