4 files changed, 65 insertions, 5 deletions
diff --git a/llvm/lib/CodeGen/LiveDebugValues.cpp b/llvm/lib/CodeGen/LiveDebugValues.cpp
index 033394fb0f5..1ddcceabe20 100644
--- a/llvm/lib/CodeGen/LiveDebugValues.cpp
+++ b/llvm/lib/CodeGen/LiveDebugValues.cpp
@@ -77,6 +77,7 @@ using namespace llvm;
 #define DEBUG_TYPE "livedebugvalues"
 
 STATISTIC(NumInserted, "Number of DBG_VALUE instructions inserted");
+STATISTIC(NumRemoved, "Number of DBG_VALUE instructions removed");
 
 // If @MI is a DBG_VALUE with debug value described by a defined
 // register, returns the number of this register. In the other case, returns 0.
@@ -942,7 +943,7 @@ bool LiveDebugValues::transferTerminator(MachineBasicBlock *CurMBB,
     VarLocIDs[ID].dump();
   });
   VarLocSet &VLS = OutLocs[CurMBB];
-  Changed = VLS |= OpenRanges.getVarLocs();
+  Changed = VLS != OpenRanges.getVarLocs();
   // New OutLocs set may be different due to spill, restore or register
   // copy instruction processing.
   if (Changed)
@@ -1101,8 +1102,6 @@ bool LiveDebugValues::join(
   // is the entry block which has no predecessor.
   assert((NumVisited || MBB.pred_empty()) &&
          "Should have processed at least one predecessor");
-  if (InLocsT.empty())
-    return false;
 
   VarLocSet &ILS = InLocs[&MBB];
   VarLocSet &Pending = PendingInLocs[&MBB];
@@ -1118,6 +1117,19 @@ bool LiveDebugValues::join(
     ++NumInserted;
     Changed = true;
   }
+
+  // We may have lost locations by learning about a predecessor that either
+  // loses or moves a variable. Find any locations in ILS that are not in the
+  // new in-locations, and delete those.
+  VarLocSet Removed = ILS;
+  Removed.intersectWithComplement(InLocsT);
+  for (auto ID : Removed) {
+    Pending.reset(ID);
+    ILS.reset(ID);
+    ++NumRemoved;
+    Changed = true;
+  }
+
   return Changed;
 }
 
diff --git a/llvm/test/DebugInfo/COFF/pieces.ll b/llvm/test/DebugInfo/COFF/pieces.ll
index f864931a290..2fcc5b70317 100644
--- a/llvm/test/DebugInfo/COFF/pieces.ll
+++ b/llvm/test/DebugInfo/COFF/pieces.ll
@@ -43,7 +43,6 @@
 ; ASM: [[oy_ox_start:\.Ltmp[0-9]+]]:
 ; ASM:         .p2align        4, 0x90
 ; ASM: .LBB0_3:                                # %for.body
-; ASM:        #DEBUG_VALUE: loop_csr:o <- [DW_OP_LLVM_fragment 0 32] 0
 ; ASM:        #DEBUG_VALUE: loop_csr:o <- [DW_OP_LLVM_fragment 0 32] $edi
 ; ASM:        #DEBUG_VALUE: loop_csr:o <- [DW_OP_LLVM_fragment 32 32] $esi
 ; ASM:        .cv_loc 0 1 13 11               # t.c:13:11
diff --git a/llvm/test/DebugInfo/X86/fission-ranges.ll b/llvm/test/DebugInfo/X86/fission-ranges.ll
index 106834d9284..c2b355b994c 100644
--- a/llvm/test/DebugInfo/X86/fission-ranges.ll
+++ b/llvm/test/DebugInfo/X86/fission-ranges.ll
@@ -45,7 +45,7 @@
 ; if they've changed due to a bugfix, change in register allocation, etc.
 
 ; CHECK:      [[A]]:
-; CHECK-NEXT:   Addr idx 2 (w/ length 169): DW_OP_consts +0, DW_OP_stack_value
+; CHECK-NEXT:   Addr idx 2 (w/ length 15): DW_OP_consts +0, DW_OP_stack_value
 ; CHECK-NEXT:   Addr idx 3 (w/ length 15): DW_OP_reg0 RAX
 ; CHECK-NEXT:   Addr idx 4 (w/ length 18): DW_OP_breg7 RSP-8
 ; CHECK:      [[E]]:
diff --git a/llvm/test/DebugInfo/X86/live-debug-values-remove-range.ll b/llvm/test/DebugInfo/X86/live-debug-values-remove-range.ll
new file mode 100644
index 00000000000..3d5219e74c1
--- /dev/null
+++ b/llvm/test/DebugInfo/X86/live-debug-values-remove-range.ll
@@ -0,0 +1,49 @@
+; RUN: llc -mtriple=x86_64-unknown-unknown %s -o - -stop-after=livedebugvalues | FileCheck %s
+;
+; In the simple loop below, the location of the variable "toast" is %bar in
+; the entry block, then set to constant zero at the end of the loop. We cannot
+; know the location of "toast" at the start of the %loop block. Test that no
+; location is given until after the call to @booler.
+;
+; CHECK: ![[VARNUM:[0-9]+]] = !DILocalVariable(name: "toast"
+;
+; CHECK-LABEL: bb.1.loop
+; CHECK-NOT:   DBG_VALUE
+; CHECK-LABEL: CALL64pcrel32 @booler
+; CHECK:       DBG_VALUE 0, $noreg, ![[VARNUM]]
+
+declare i1 @booler()
+declare void @escape(i32)
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+@glob = global i32 0
+
+define i32 @foo(i32 %bar) !dbg !4 {
+entry:
+  call void @llvm.dbg.value(metadata i32 %bar, metadata !3, metadata !DIExpression()), !dbg !6
+  br label %loop
+loop:
+  call void @escape(i32 %bar)
+  %retval = call i1 @booler(), !dbg !6
+  call void @llvm.dbg.value(metadata i32 0, metadata !3, metadata !DIExpression()), !dbg !6
+  br i1 %retval, label %loop2, label %exit
+loop2:
+  store i32 %bar, i32 *@glob
+  br label %loop
+exit:
+  ret i32 %bar
+}
+
+!llvm.module.flags = !{!0, !100}
+!llvm.dbg.cu = !{!1}
+
+!100 = !{i32 2, !"Dwarf Version", i32 4}
+!0 = !{i32 2, !"Debug Info Version", i32 3}
+!1 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !2, producer: "beards", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug)
+!2 = !DIFile(filename: "bees.cpp", directory: ".")
+!3 = !DILocalVariable(name: "toast", scope: !4, file: !2, line: 1, type: !16)
+!4 = distinct !DISubprogram(name: "nope", scope: !2, file: !2, line: 1, spFlags: DISPFlagDefinition, unit: !1, retainedNodes: !13, type: !14, isDefinition: true)
+!6 = !DILocation(line: 1, scope: !4)
+!13 = !{!3}
+!14 = !DISubroutineType(types: !15)
+!15 = !{!16}
+!16 = !DIBasicType(name: "int", size: 32, align: 32, encoding: DW_ATE_signed)