[LiveDebugValues] 4/4 Initial test changes for InstrRef LiveDebugValues

[jmorse]

Summary

(Context: this thread http://lists.llvm.org/pipermail/llvm-dev/2020-June/142368.html )

This patch contains a bunch of test changes to account for changes in output from the new instruction-referencing LiveDebugValues. It doesn't make all tests pass if you manually demand the new LiveDebugValues -- there are still some limitations, for example I haven't attempted entry values (yet). IMHO, it's Good Enough (TM) to be in-tree, even if it isn't 100% complete yet.

About 85% of the changes here are to CHECK lines that have a trailing !debug-location: InstrRef LDV generates a DILocation for new DBG_VALUEs with only a scope, instead of copying a previous DBG_VALUEs DebugLoc, and that leads to the location being printed as:

!debug-location !DILocation(line: 0, blah blah)

instead of

!debug-location !1234

The changes in this patch just chop off the !debug-location check. I guess it's arguable as to what kind of DebugLoc we want for propagated DBG_VALUEs. At the very least though, they don't affect output DWARF.

This patch additionally fiddles with:

• kill-after-spill.mir , where I've added a source location to each block in the program. InstrRef LDV refuses to propagate variable locations as far as the old one did, when the variables are out of scope,
• live-debug-values-bad-transfer.mir where a known bug/limitation has been fixed, I've added instrref-and-varloc expected outputs to test for.

Finally I've added two new tests:

• livedebugvalues_load_in_loop.mir , which shows off some multiple-location value tracking in action on a totally contrived input,
• livedebugvalues_many_loop_heads.mir , which demonstrates a pathological input to InstrRef LDV, as explained in the test file comment.

I've got a list of other inputs that InstrRef LDV finds difficult and want coverage, but they're not submittable-quality yet. I felt it was important to get this out now and add additional tests later, if people are happy with that.

[jmorse]

Add three new tests of interesting (TM) LiveDebugValues input, which I'll refer to in D83047:

llvm/test/DebugInfo/MIR/InstrRef/livedebugvalues_downgradefeedback_loop.mir
llvm/test/DebugInfo/MIR/InstrRef/livedebugvalues_insensitive_downgrade.mir
llvm/test/DebugInfo/MIR/InstrRef/livedebugvalues_path_lengths.mir

[djtodoro]

llvm/test/DebugInfo/MIR/InstrRef/livedebugvalues_insensitive_downgrade.mir

76 ↗

(On Diff #280457)

I guess we do not need all the MF attributes here.

[jmorse]

Thanks to all the reviewers in this series for their time!

llvm/test/DebugInfo/MIR/Mips/last-inst-bundled.mir

 #}
 #
 # reproduce:
 # clang --target=mips-linux-gnu -g -O1 -S -emit-llvm last-instr-bundled
 # llc -stop-before=livedebugvalues < last-instr-bundled.ll > last-instr-bundled.mir
 #
 # Check that last bundled instruction of block gets recognized as end of basic block.
 # CHECK: bb.2.if.end
-# CHECK-NEXT: DBG_VALUE $s0, $noreg, !12, !DIExpression(), debug-location !17
+# CHECK-NEXT: DBG_VALUE $s0, $noreg, !12, !DIExpression()
 
 --- |
   ; ModuleID = '<stdin>'
   source_filename = "last-inst-bundled.c"
   target datalayout = "E-m:m-p:32:32-i8:8:32-i16:16:32-i64:64-n32-S64"
   target triple = "mips--linux-gnu"
 
   define void @foo(i32 signext %argument) local_unnamed_addr !dbg !7 {

llvm/test/DebugInfo/MIR/X86/kill-after-spill.mir

 # RUN: llc -run-pass=livedebugvalues -o - %s | FileCheck %s
 #
 # This test is used to acknowledge situation when spill register is killed
 # in instruction after the spill occurs.
 # Generated MIR is changed in order to test case when instruction after
 # possible spill, say instruction B, kills register different than than
 # the one that is used in possible spill, say instruction A. In that case
 # the instruction A is not recognized as spill. Changed instructions are
 # commented in MIR below.
 #
 # ...
 # A - possible spill instruction with register R2
 # B - instruction that kills R3
 # ...
 #
 # CHECK: bb.1.if.end:
-# CHECK: DBG_VALUE $rbp, 0, !37, !DIExpression(DW_OP_constu, 44, DW_OP_minus), debug-location !58
-# CHECK-NOT: DBG_VALUE $rbp, 0, !36, !DIExpression(DW_OP_constu, 48, DW_OP_minus), debug-location !57
+# CHECK: DBG_VALUE $rbp, 0, !37, !DIExpression(DW_OP_constu, 44, DW_OP_minus)
+# CHECK-NOT: DBG_VALUE $rbp, 0, !36, !DIExpression(DW_OP_constu, 48, DW_OP_minus)
 
 --- |
   ; ModuleID = '<stdin>'
   source_filename = "<stdin>"
   target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
   target triple = "x86_64-unknown-linux-gnu"
 
   %struct.firstStruct = type { i32, i8, %struct.secondStruct* }
bb.0.entry:
     $r15d = MOV32rr $edi
     DBG_VALUE $r15d, $noreg, !36, !DIExpression(), debug-location !57
     renamable $r14 = MOV64ri -9223372036854775808
     $edi = MOV32rr $ebx
     CALL64pcrel32 @func1, csr_64, implicit $rsp, implicit $ssp, implicit $edi, implicit-def $rsp, implicit-def $ssp, implicit-def $rax
     $r13 = MOV64rr $rax
     renamable $ecx = XOR32rr undef $ecx, undef $ecx, implicit-def dead $eflags
     renamable $r13 = AND64rr killed renamable $r13, renamable $r14, implicit-def $eflags
-    JCC_1 %bb.9, 4, implicit $eflags
+    JCC_1 %bb.9, 4, implicit $eflags, debug-location !57
 
   bb.1.if.end:
     successors: %bb.2(0x30000000), %bb.3(0x50000000)
     liveins: $ebx, $r13, $r14, $r15d
 
     ; The instruction below is inserted additionally in order to test part of the code.
     $r12d = MOV32rr $r15d
     MOV32mr $rbp, 1, $noreg, -48, $noreg, renamable $r15d :: (store 4 into %stack.0)
     ; The instruction below is altered ($r15d -> $r12d) in order to test part of the code.
     ; The original instruction "$edi = MOV32rr killed $r15d
     $edi = MOV32rr killed $r12d
     MOV32mr $rbp, 1, $noreg, -44, $noreg, renamable $ebx :: (store 4 into %stack.1)
     $esi = MOV32rr killed $ebx
     CALL64pcrel32 @func2, csr_64, implicit $rsp, implicit $ssp, implicit $edi, implicit $esi, implicit-def $rsp, implicit-def $ssp, implicit-def $rax
     $r12 = MOV64rr $rax
     $r15 = MOV64rr $r12
     renamable $r15 = AND64ri8 killed renamable $r15, -123, implicit-def $eflags
-    JCC_1 %bb.2, 4, implicit $eflags
+    JCC_1 %bb.2, 4, implicit $eflags, debug-location !57
 
   bb.3.private.exit:
     successors: %bb.9(0x30000000), %bb.4(0x50000000)
     liveins: $r12, $r13, $r14, $r15
 
     renamable $r14 = OR64rr killed renamable $r14, renamable $r12, implicit-def dead $eflags
     $esi = XOR32rr undef $esi, undef $esi, implicit-def dead $eflags
     dead $edx = MOV32ri 16, implicit-def $rdx
     $rdi = MOV64rr killed $r14
     CALL64pcrel32 @memset, csr_64, implicit $rsp, implicit $ssp, implicit $rdi, implicit $esi, implicit $rdx, implicit-def $rsp, implicit-def $ssp, implicit-def dead $rax
     $rdi = MOV64rr $r12
     CALL64pcrel32 @func4, csr_64, implicit $rsp, implicit $ssp, implicit $rdi, implicit-def $rsp, implicit-def $ssp, implicit-def $eax
     renamable $ecx = MOV32ri 1
     TEST32rr killed renamable $eax, renamable $eax, implicit-def $eflags
-    JCC_1 %bb.9, 4, implicit $eflags
+    JCC_1 %bb.9, 4, implicit $eflags, debug-location !57
 
   bb.4.if.then8:
     successors: %bb.8(0x30000000), %bb.5(0x50000000)
     liveins: $r12, $r13, $r15
 
     $esi = XOR32rr undef $esi, undef $esi, implicit-def dead $eflags
     $rdi = MOV64rr $r12
     CALL64pcrel32 @func5, csr_64, implicit $rsp, implicit $ssp, implicit $rdi, implicit $esi, implicit-def $rsp, implicit-def $ssp
     renamable $rax = MOV64rm killed renamable $r13, 1, $noreg, 8, $noreg :: (load 8 from %ir.13)
     TEST64rr renamable $rax, renamable $rax, implicit-def $eflags
-    JCC_1 %bb.8, 4, implicit $eflags
+    JCC_1 %bb.8, 4, implicit $eflags, debug-location !57
 
   bb.5.land.lhs.true:
     successors: %bb.6(0x30000000), %bb.7(0x50000000)
     liveins: $rax, $r12, $r15
 
     CMP32mi8 renamable $r15, 1, $noreg, 0, $noreg, 0, implicit-def $eflags :: (load 4 from %ir.tot_perf2, align 8)
-    JCC_1 %bb.7, 5, implicit $eflags
+    JCC_1 %bb.7, 5, implicit $eflags, debug-location !57
 
   bb.6.lor.lhs.false:
     successors: %bb.8(0x30000000), %bb.7(0x50000000)
     liveins: $rax, $r12, $r15
 
     CMP32mi8 killed renamable $r15, 1, $noreg, 4, $noreg, 0, implicit-def $eflags :: (load 4 from %ir.tot_bw)
-    JCC_1 %bb.8, 4, implicit $eflags
+    JCC_1 %bb.8, 4, implicit $eflags, debug-location !57
 
   bb.7.if.then14:
     successors: %bb.8(0x80000000)
     liveins: $rax, $r12
 
     renamable $rdx = MOV64rm killed renamable $rax, 1, $noreg, 8, $noreg :: (load 8 from %ir.20)
     $rdi = MOV64rr killed $r12
     $esi = MOV32rm $rbp, 1, $noreg, -44, $noreg :: (load 4 from %stack.1)
-    CALL64pcrel32 @func6, csr_64, implicit $rsp, implicit $ssp, implicit $rdi, implicit $esi, implicit $rdx, implicit-def $rsp, implicit-def $ssp
+    CALL64pcrel32 @func6, csr_64, implicit $rsp, implicit $ssp, implicit $rdi, implicit $esi, implicit $rdx, implicit-def $rsp, implicit-def $ssp, debug-location !57
 
   bb.8.cleanup:
     successors: %bb.9(0x80000000)
 
     renamable $ecx = MOV32ri 1
-    JMP_1 %bb.9
+    JMP_1 %bb.9, debug-location !57
 
   bb.2.if.then3:
     successors: %bb.9(0x80000000)
     liveins: $r13
 
     renamable $edi = MOV32rm renamable $r13, 1, $noreg, 0, $noreg :: (load 4 from %ir.variableLocal11, align 8)
     renamable $esi = MOVZX32rm8 killed renamable $r13, 1, $noreg, 4, $noreg :: (load 1 from %ir.variableLocal2, align 4)
     renamable $ecx = MOV32ri @.str, implicit-def $rcx
     renamable $rcx = OR64ri32 killed renamable $rcx, -92238, implicit-def dead $eflags
     $edx = MOV32ri 5
     $r8d = MOV32rm $rbp, 1, $noreg, -48, $noreg :: (load 4 from %stack.0)
     CALL64pcrel32 @func3, csr_64, implicit $rsp, implicit $ssp, implicit $edi, implicit $esi, implicit $edx, implicit $rcx, implicit $r8d, implicit-def $rsp, implicit-def $ssp
-    renamable $ecx = XOR32rr undef $ecx, undef $ecx, implicit-def dead $eflags
+    renamable $ecx = XOR32rr undef $ecx, undef $ecx, implicit-def dead $eflags, debug-location !57
 
   bb.9.cleanup:
     liveins: $ecx
 
     $eax = MOV32rr killed $ecx
     $rsp = ADD64ri8 $rsp, 8, implicit-def dead $eflags
     $rbx = POP64r implicit-def $rsp, implicit $rsp
     $r12 = POP64r implicit-def $rsp, implicit $rsp
     $r13 = POP64r implicit-def $rsp, implicit $rsp
     $r14 = POP64r implicit-def $rsp, implicit $rsp
     $r15 = POP64r implicit-def $rsp, implicit $rsp
     $rbp = POP64r implicit-def $rsp, implicit $rsp
-    RETQ $eax
+    RETQ $eax, debug-location !57
 
 ...

llvm/test/DebugInfo/MIR/X86/live-debug-values-3preds.mir

 
 # CHECK: ![[X_VAR:[0-9]+]] = !DILocalVariable(name: "x", {{.*}})
 # CHECK: ![[Y_VAR:[0-9]+]] = !DILocalVariable(name: "y", {{.*}})
 # CHECK: ![[Z_VAR:[0-9]+]] = !DILocalVariable(name: "z", {{.*}})
 
 # DBG_VALUE for variables "x", "y" and "z" are extended into %bb.9 from its
 # predecessors %bb.0, %bb.2 and %bb.8.
 # CHECK:      bb.9.for.end:
-# CHECK-DAG:  DBG_VALUE $edi, $noreg, ![[X_VAR]], !DIExpression(), debug-location !{{[0-9]+}}
-# CHECK-DAG:  DBG_VALUE $esi, $noreg, ![[Y_VAR]], !DIExpression(), debug-location !{{[0-9]+}}
-# CHECK-DAG:  DBG_VALUE $edx, $noreg, ![[Z_VAR]], !DIExpression(), debug-location !{{[0-9]+}}
+# CHECK-DAG:  DBG_VALUE $edi, $noreg, ![[X_VAR]], !DIExpression()
+# CHECK-DAG:  DBG_VALUE $esi, $noreg, ![[Y_VAR]], !DIExpression()
+# CHECK-DAG:  DBG_VALUE $edx, $noreg, ![[Z_VAR]], !DIExpression()
 # CHECK:      RET
 
 --- |
   ; ModuleID = 'live-debug-values-3preds.ll'
   target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
   target triple = "x86_64-unknown-linux-gnu"
   
   ; Function Attrs: norecurse nounwind readnone uwtable

llvm/test/DebugInfo/MIR/X86/live-debug-values-bad-transfer.mir

 # RUN: llc %s -mtriple=x86_64-unknown-unknown -o - -run-pass=livedebugvalues | FileCheck %s --implicit-check-not=DBG_VALUE
+# RUN: llc %s -mtriple=x86_64-unknown-unknown -o - -run-pass=livedebugvalues -experimental-debug-variable-locations | FileCheck %s -check-prefix=NEWLDV --implicit-check-not=DBG_VALUE
 #
 # Test that the DBG_VALUE of ecx below does not get propagated. It is considered
 # live-in on LiveDebugValues' first pass through the loop, but on the second it
 # should be removed from the InLocs set because it gets clobbered inside the
 # loop. There should be no transfer from ecx to ebx -- this is ensured by the
 # FileCheck implicit-check-not option.
 #
 # FIXME: we successfully prevent the false location (ebx) from being
 # propagated into block 2, but the original transfer isn't yet eliminated.
 # Thus we get no DBG_VALUe in block 2, but an invalid one in block 1.
 #
 # CHECK-LABEL: name: foo
 # CHECK-LABEL: bb.0.entry:
 # CHECK:       $ecx = MOV32ri 0
 # CHECK-NEXT:  DBG_VALUE
 # CHECK-LABEL: bb.1.loop:
 # CHECK:       $ebx = COPY killed $ecx
 # CHECK-NEXT:  DBG_VALUE
+#
+# This doesn't occur under value-tracking LiveDebugValues though.
+#
+# NEWLDV-LABEL: name: foo
+# NEWLDV-LABEL: bb.0.entry:
+# NEWLDV:       $ecx = MOV32ri 0
+# NEWLDV-NEXT:  DBG_VALUE
 
 --- |
   source_filename = "live-debug-values-remove-range.ll"
   target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
   
   declare void @llvm.dbg.value(metadata, metadata, metadata)
   
   define i32 @foo(i32 %bar) !dbg !4 {

 body:             |
   bb.0.entry:
     liveins: $edi, $rbx
   
     frame-setup PUSH64r killed $rbx, implicit-def $rsp, implicit $rsp
     CFI_INSTRUCTION def_cfa_offset 16
     CFI_INSTRUCTION offset $rbx, -16
     $ebx = MOV32rr $edi
-    $eax = MOV32ri 0
-    $ecx = MOV32ri 0
+    $eax = MOV32ri 0, debug-location !10
+    $ecx = MOV32ri 0, debug-location !10
     DBG_VALUE $ecx, $noreg, !9, !DIExpression(), debug-location !10
-    $edi = MOV32ri 0
-    $esi = MOV32ri 0
+    $edi = MOV32ri 0, debug-location !10
+    $esi = MOV32ri 0, debug-location !10
   
   bb.1.loop:
     successors: %bb.1, %bb.2
     liveins: $ebx, $eax, $ecx, $edi, $esi
   
-    $eax = COPY $ecx
-    $ebx = COPY killed $ecx
-    $ecx = COPY killed $edi
-    $edi = COPY killed $esi
-    $esi = MOV32ri 1
+    $eax = COPY $ecx, debug-location !10
+    $ebx = COPY killed $ecx, debug-location !10
+    $ecx = COPY killed $edi, debug-location !10
+    $edi = COPY killed $esi, debug-location !10
+    $esi = MOV32ri 1, debug-location !10
     TEST8ri killed renamable $al, 1, implicit-def $eflags
-    JCC_1 %bb.1, 5, implicit killed $eflags
+    JCC_1 %bb.1, 5, implicit killed $eflags, debug-location !10
   
   bb.2.exit:
     liveins: $ebx
   
-    $eax = MOV32rr killed $ebx
+    $eax = MOV32rr killed $ebx, debug-location !10
     $rbx = frame-destroy POP64r implicit-def $rsp, implicit $rsp
     CFI_INSTRUCTION def_cfa_offset 8
-    RETQ $eax
+    RETQ $eax, debug-location !10
 
 ...

llvm/test/DebugInfo/MIR/X86/live-debug-values.mir

 # llvm/test/DebugInfo/live-debug-values.ll and present here for testing under
 # MIR->MIR serialization.
 
 # DBG_VALUE for variable "n" is extended into %bb.5 from its predecessors %bb.3
 # and %bb.4.
 # CHECK: ![[N_VAR:[0-9]+]] = !DILocalVariable(name: "n",{{.*}})
 #
 # CHECK:      bb.5.if.end.7:
-# CHECK:        DBG_VALUE $ebx, $noreg, ![[N_VAR]], !DIExpression(), debug-location !{{[0-9]+}}
+# CHECK:        DBG_VALUE $ebx, $noreg, ![[N_VAR]], !DIExpression()
 
 
 --- |
   ; ModuleID = 'live-debug-values.ll'
   target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
   target triple = "x86_64-unknown-linux-gnu"
   
   @m = common global i32 0, align 4, !dbg !16

llvm/test/DebugInfo/MIR/X86/livedebugvalues-ignores-metaInstructions.mir

 --- |
   ; RUN: llc %s -march=x86-64 -run-pass=livedebugvalues -o - | FileCheck %s -implicit-check-not=DBG_VALUE
 
   ; Check that live-debug-values ignores meta instructions.
 
   ; CHECK-LABEL: bb.0.entry:
   ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
   ; CHECK-LABEL: bb.1.bb1:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.2.bb2:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.3.bb3:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !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

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

 --- |
   ; RUN: llc %s -march=x86-64 -run-pass=livedebugvalues -o - | FileCheck %s -implicit-check-not=DBG_VALUE
 
   ; Check that DBG_VALUE instructions are propogated through a CFG containing
   ; a diamond that doesn't move or clobber their locations.
 
   ; CHECK-LABEL: bb.0.entry:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.1.bb1:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.2.bb2:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.3.bb3:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !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

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

 --- |
   ; RUN: llc %s -march=x86-64 -run-pass=livedebugvalues -o - | FileCheck %s -implicit-check-not=DBG_VALUE
 
   ; Check that DBG_VALUE instructions are only propogated into the top blocks of
   ; a diamond when the location is clobbered and not into the successor block.
 
   ; CHECK-LABEL: bb.0.entry:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.1.bb1:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-NEXT:  $ebx = MOV32ri 0, debug-location !17
   ; CHECK-LABEL: bb.2.bb2:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-NEXT:  $ebx = MOV32ri 0, debug-location !17
 
   define i32 @_Z8bb_to_bb() local_unnamed_addr !dbg !12 {
   entry:
     br label %bb1, !dbg !17
   bb1:
     br label %bb2, !dbg !17
   bb2:

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

 --- |
   ; RUN: llc %s -march=x86-64 -run-pass=livedebugvalues -o - | FileCheck %s -implicit-check-not=DBG_VALUE
 
   ; Check that DBG_VALUE instructions are propogated correctly through a
   ; diamond CFG when the location is moved by another instruction.
 
   ; CHECK-LABEL: bb.0.entry:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.1.bb1:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-NEXT:  $eax = MOV32ri 0, debug-location !17
-  ; CHECK-NEXT:  DBG_VALUE $eax, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK-NEXT:  DBG_VALUE $eax, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.2.bb2:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-NEXT:  $eax = MOV32ri 0, debug-location !17
-  ; CHECK-NEXT:  DBG_VALUE $eax, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK-NEXT:  DBG_VALUE $eax, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.3.bb3:
-  ; CHECK:       DBG_VALUE $eax, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $eax, $noreg, !16, !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

llvm/test/DebugInfo/MIR/X86/livedebugvalues_basic_diamond_one_clobber.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 successor block
   ; of a diamond CFG that clobbers its location.
 
   ; CHECK-LABEL: bb.0.entry:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.1.bb1:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.2.bb2:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !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

llvm/test/DebugInfo/MIR/X86/livedebugvalues_basic_diamond_one_move.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 successor block
   ; of a diamond CFG that moves its location.
 
   ; CHECK-LABEL: bb.0.entry:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.1.bb1:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-NEXT:  $eax = MOV32ri 0, debug-location !17
-  ; CHECK:       DBG_VALUE $eax, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $eax, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.2.bb2:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !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

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

 --- |
   ; RUN: llc %s -march=x86-64 -run-pass=livedebugvalues -o - | FileCheck %s -implicit-check-not=DBG_VALUE
 
   ; Check that DBG_VALUE instructions are propagated throughout a CFG with a
   ; loop that doesn't move or clobber its location.
 
   ; CHECK-LABEL: bb.0.entry:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.1.bb1:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.2.bb2:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.3.bb3:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !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

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

 --- |
   ; RUN: llc %s -march=x86-64 -run-pass=livedebugvalues -o - | FileCheck %s -implicit-check-not=DBG_VALUE
 
   ; Check that DBG_VALUE instructions are propagated throughout a basic
   ; sequential CFG.
 
   ; CHECK-LABEL: bb.0.entry:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.1.bb1:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.2.bb2:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.3.bb3:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !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

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

 --- |
   ; RUN: llc %s -march=x86-64 -run-pass=livedebugvalues -o - | FileCheck %s -implicit-check-not=DBG_VALUE
 
   ; Check that DBG_VALUE instructions are propagated into basic blocks with no
   ; control flow when it's location is clobbered.
 
   ; CHECK-LABEL: bb.0.entry:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.1.bb1:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !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

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

 --- |
   ; RUN: llc %s -march=x86-64 -run-pass=livedebugvalues -o - | FileCheck %s -implicit-check-not=DBG_VALUE
 
   ; Check that DBG_VALUE instructions are correctly propagated into blocks with
   ; no control flow when a location is moved and then clobbered.
 
   ; CHECK-LABEL: bb.0.entry:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.1.bb1:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-NEXT:  $eax = MOV32ri 0, debug-location !17
-  ; CHECK:       DBG_VALUE $eax, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $eax, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.2.bb2:
-  ; CHECK:       DBG_VALUE $eax, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $eax, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.3.bb3:
 
   define i32 @_Z8bb_to_bb() local_unnamed_addr !dbg !12 {
   entry:
     br label %bb1, !dbg !17
   bb1:
     br label %bb2, !dbg !17
   bb2:

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

+--- |
+  ; RUN: llc %s -march=x86-64 -run-pass=livedebugvalues -o - -experimental-debug-variable-locations -emulate-old-livedebugvalues=0 | FileCheck %s -implicit-check-not=DBG_VALUE
+
+  ; Sometimes, variables can have multiple locations, and when control flow
+  ; merges LiveDebugValues has a hard time picking which one the variable lives
+  ; in. Test two of these scenarios that old LiveDebugValues can't handle: when
+  ; a value is in two registers, and when a value is both in a register and
+  ; on the stack.
+
+  ; In a register:
+
+  ; CHECK-LABEL: bb.0.entry:
+  ; CHECK:       DBG_VALUE $rdi, $noreg, !16, !DIExpression()
+  ; CHECK-LABEL: bb.1.bb1:
+  ; CHECK:       DBG_VALUE $rbp, $noreg, !16, !DIExpression()
+  ; CHECK:       DBG_VALUE $rbp, $noreg, !16, !DIExpression()
+  ; CHECK-LABEL: bb.2.bb2:
+  ; CHECK:       DBG_VALUE $rbp, $noreg, !16, !DIExpression()
+  ; CHECK-LABEL: bb.3.bb3:
+  ; CHECK:       DBG_VALUE $rbp, $noreg, !16, !DIExpression()
+
+  ; On the stack: we move from $rbp to a stack slot in bb4, but join back on
+  ; $rbp in bb6.
+
+  ; CHECK-LABEL: bb.4:
+  ; CHECK:       DBG_VALUE $rbp, $noreg, !16, !DIExpression()
+  ; CHECK:       DBG_VALUE $rsp, 0, !16, !DIExpression()
+  ; CHECK-LABEL: bb.5:
+  ; CHECK:       DBG_VALUE $rbp, $noreg, !16, !DIExpression()
+  ; CHECK-LABEL: bb.6:
+  ; CHECK:       DBG_VALUE $rbp, $noreg, !16, !DIExpression()
+
+  declare i64 @bees(i64 %arg);
+
+  define i32 @_Z8bb_to_bb(i64 %arg) local_unnamed_addr !dbg !12 {
+  entry:
+    br label %bb1, !dbg !17
+  bb1:
+    br label %bb2, !dbg !17
+  bb2:
+    br label %bb3, !dbg !17
+  bb3:
+    ret i32 0, !dbg !17
+  }
+
+  !llvm.dbg.cu = !{!0}
+  !llvm.module.flags = !{!7, !8, !9, !10}
+  !llvm.ident = !{!11}
+  !0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 10.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, globals: !3, debugInfoForProfiling: true, nameTableKind: None)
+  !1 = !DIFile(filename: "main.cpp", directory: "F:\")
+  !2 = !{}
+  !3 = !{!4}
+  !4 = !DIGlobalVariableExpression(var: !5, expr: !DIExpression())
+  !5 = distinct !DIGlobalVariable(name: "start", scope: !0, file: !1, line: 4, type: !6, isLocal: false, isDefinition: true)
+  !6 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+  !7 = !{i32 2, !"Dwarf Version", i32 4}
+  !8 = !{i32 2, !"Debug Info Version", i32 3}
+  !9 = !{i32 1, !"wchar_size", i32 2}
+  !10 = !{i32 7, !"PIC Level", i32 2}
+  !11 = !{!"clang version 10.0.0"}
+  !12 = distinct !DISubprogram(name: "bb_to_bb", linkageName: "bb_to_bb", scope: !1, file: !1, line: 6, type: !13, scopeLine: 6, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !15)
+  !13 = !DISubroutineType(types: !14)
+  !14 = !{!6, !6}
+  !15 = !{!16}
+  !16 = !DILocalVariable(name: "myVar", scope: !12, file: !1, line: 7, type: !6)
+  !17 = !DILocation(line: 10, scope: !12)
+
+...
+---
+name: _Z8bb_to_bb
+tracksRegLiveness: true
+liveins:
+  - { reg: '$rdi', virtual-reg: '' }
+stack:
+  - { id: 0, name: '', type: spill-slot, offset: -8, size: 8, alignment: 8,
+      stack-id: default, callee-saved-register: '', callee-saved-restored: true,
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+body:  |
+  bb.0.entry:
+  liveins: $rdi
+    successors: %bb.1, %bb.2
+    DBG_VALUE $rdi, $noreg, !16, !DIExpression(), debug-location !17
+    $rbp = MOV64rr $rdi, debug-location !17
+    dead $rcx = MOV64ri 0, debug-location !17
+    CALL64pcrel32 @bees, csr_64, implicit $rsp, implicit $ssp, implicit $rdi, implicit-def $rsp, implicit-def $ssp, implicit-def $rax, debug-location !17
+    CMP64ri8 renamable $rax, 1, implicit-def $eflags, debug-location !17
+    JCC_1 %bb.2, 4, implicit killed $eflags, debug-location !17
+  bb.1.bb1:
+  liveins: $rax, $rbp
+    successors: %bb.3
+    $rbp = MOV64ri 0, debug-location !17
+    DBG_VALUE $rbp, $noreg, !16, !DIExpression(), debug-location !17
+    JMP_1 %bb.3
+  bb.2.bb2:
+  liveins: $rax, $rbp
+    successors: %bb.3
+    $rax = MOV64ri 0, debug-location !17
+  bb.3.bb3:
+  liveins: $rax, $rbp
+    $rdi = MOV64rr $rbp, debug-location !17
+    CALL64pcrel32 @bees, csr_64, implicit $rsp, implicit $ssp, implicit $rdi, implicit-def $rsp, implicit-def $ssp, implicit-def $rax, debug-location !17
+    CMP64ri8 renamable $rax, 1, implicit-def $eflags, debug-location !17
+    JCC_1 %bb.5, 4, implicit killed $eflags, debug-location !17
+  bb.4:
+  liveins: $rax, $rbp
+    MOV64mr $rsp, 1, $noreg, 8, $noreg, killed renamable $rbp :: (store 8 into %stack.0)
+    JMP_1 %bb.6
+  bb.5:
+  liveins: $rax, $rbp
+  bb.6:
+  liveins: $rax, $rbp
+    RETQ $rax, debug-location !17
+...

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

 --- |
   ; RUN: llc %s -march=x86-64 -run-pass=livedebugvalues -o - | FileCheck %s -implicit-check-not=DBG_VALUE
 
   ; Check that DBG_VALUE instructions are correctly propagated into a loop with
   ; break.
 
   ; CHECK-LABEL: bb.0.entry:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.1.bb1:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.2.bb2:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.3.bb3:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.4.bb4:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !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

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

 --- |
   ; RUN: llc %s -march=x86-64 -run-pass=livedebugvalues -o - | FileCheck %s -implicit-check-not=DBG_VALUE
 
   ; Check that DBG_VALUE instructions are propagated into a loop with
   ; diamond pattern and beyond.
 
   ; CHECK-LABEL: bb.0.entry:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.1.bb1:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.2.bb2:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.3.bb3:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.4.bb4:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.5.bb5:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !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

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

 --- |
   ; RUN: llc %s -march=x86-64 -run-pass=livedebugvalues -o - | FileCheck %s -implicit-check-not=DBG_VALUE
 
   ; Check that DBG_VALUE instructions are propagated into a loop with
   ; diamond pattern but not beyond.
 
   ; CHECK-LABEL: bb.0.entry:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.1.bb1:
-  ; CHECK:       DBG_VALUE $eax, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $eax, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.2.bb2:
-  ; CHECK:       DBG_VALUE $eax, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $eax, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.3.bb3:
-  ; CHECK:       DBG_VALUE $eax, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $eax, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.4.bb4:
-  ; CHECK:       DBG_VALUE $eax, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $eax, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.5.bb5:
-  ; CHECK:       DBG_VALUE $eax, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $eax, $noreg, !16, !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

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

 --- |
   ; RUN: llc %s -march=x86-64 -run-pass=livedebugvalues -o - | FileCheck %s -implicit-check-not=DBG_VALUE
 
   ; Check that DBG_VALUE instructions are prapogated into a loop that has two
   ; backedges and beyond.
 
   ; CHECK-LABEL: bb.0.entry:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.1.bb1:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.2.bb2:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.3.bb3:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.4.bb4:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !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

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

 --- |
   ; RUN: llc %s -march=x86-64 -run-pass=livedebugvalues -o - | FileCheck %s -implicit-check-not=DBG_VALUE
 
   ; Check that DBG_VALUE instructions are propagated into loops within loops.
 
   ; CHECK-LABEL: bb.0.entry:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.1.bb1:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.2.bb2:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.3.bb3:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.4.bb4:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.5.bb5:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !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

llvm/test/DebugInfo/MIR/X86/livedebugvalues_loop_within_loop_moved.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 loops with inner
   ; loops that move their locations.
 
   ; CHECK-LABEL: bb.0.entry:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.3.bb3:
-  ; CHECK:       DBG_VALUE $eax, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $eax, $noreg, !16, !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

llvm/test/DebugInfo/MIR/X86/livedebugvalues_loop_within_loop_outer_moved.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 propogated into loops with inner
   ; loops that move their locations.
 
   ; CHECK-LABEL: bb.0.entry:
-  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $ebx, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.4.bb4:
-  ; CHECK:       DBG_VALUE $eax, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $eax, $noreg, !16, !DIExpression()
   ; CHECK-LABEL: bb.5.bb5:
-  ; CHECK:       DBG_VALUE $eax, $noreg, !16, !DIExpression(), debug-location !17
+  ; CHECK:       DBG_VALUE $eax, $noreg, !16, !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

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

+--- |
+  ; RUN: llc %s -march=x86-64 -run-pass=livedebugvalues -o - -experimental-debug-variable-locations | FileCheck %s -implicit-check-not=DBG_VALUE
+
+  ; The MIR below represents a pathalogical case for value-tracking
+  ; LiveDebugValues. The code structure is eight nested loops, with loop heads
+  ; from bb.1 to bb.8, a central block bb.9 that does nothing, and loop ends
+  ; from bb.10 to bb.17. The CMP's and jumps might be broken; the only
+  ; important part is that it looks like nested loops to LiveDebugValues.
+  ;
+  ; The variable location is always $rsi, which enters the function live.
+  ; There's also a def of $rsi in bb.14, in a loop tail, half way into the
+  ; loop nest.s.
+  ;
+  ; This presents a serious problem: the outer four loops each implicitly have
+  ; a PHI value for $rsi, because the block could be entered on a path straight
+  ; from entry, or from bb.14 where $rsi is def'd. While the innermost four
+  ; loops have a value of $rsi that is live-through each loop from bb.5
+  ; onwards.
+  ;
+  ; Value-tracking LiveDebugValues _must_ correctly identify each PHI value.
+  ; Observe the DBG_VALUE in bb.2: this variable location musn't be propagated
+  ; any further, because there's a path to either successor that goes through
+  ; bb.14 where the value is overwritten.Value tracking needs to identify the
+  ; PHI value on entry to the block; and that each successor has a different
+  ; PHI value in that register.
+  ;
+  ; Likewise, we mustn't identify values as PHIs which aren't. Entering bb.5
+  ; has a PHI value (from bb.4) in $rsi. There are no paths to bb.5 that pass
+  ; through the clobbering bb.14, which don't also pass through bb.4: thus
+  ; that value is live-through the innermost four loops. If we
+  ; over-approximated where PHIs happened, we would lose variable location
+  ; coverage here, by not propagating the variable location through the inner
+  ; loops.
+  ;
+  ; Getting this right requires the lattice descent (described in the
+  ; implementation) to search loop head PHI values, until one is found that is
+  ; live-through a loop.
+
+  ; This location in bb.2 should not be propagated further,
+  ; CHECK-LABEL: bb.2:
+  ; CHECK:  DBG_VALUE $rsi, $noreg
+
+  ; This location should be live through the inner loops, til bb.14
+  ; CHECK-LABEL: bb.5:
+  ; CHECK:  DBG_VALUE $rsi, $noreg
+  ; CHECK-LABEL: bb.6:
+  ; CHECK:  DBG_VALUE $rsi, $noreg
+  ; CHECK-LABEL: bb.7:
+  ; CHECK:  DBG_VALUE $rsi, $noreg
+  ; CHECK-LABEL: bb.8:
+  ; CHECK:  DBG_VALUE $rsi, $noreg
+  ; CHECK-LABEL: bb.9:
+  ; CHECK:  DBG_VALUE $rsi, $noreg
+  ; CHECK-LABEL: bb.10:
+  ; CHECK:  DBG_VALUE $rsi, $noreg
+  ; CHECK-LABEL: bb.11:
+  ; CHECK:  DBG_VALUE $rsi, $noreg
+  ; CHECK-LABEL: bb.12:
+  ; CHECK:  DBG_VALUE $rsi, $noreg
+  ; CHECK-LABEL: bb.13:
+  ; CHECK:  DBG_VALUE $rsi, $noreg
+
+  declare i64 @bees(i64 %arg);
+
+  define i32 @chiasm(i64 %arg) local_unnamed_addr !dbg !12 {
+  entry:
+    br label %bb1, !dbg !17
+  bb1:
+    br label %bb2, !dbg !17
+  bb2:
+    br label %bb3, !dbg !17
+  bb3:
+    ret i32 0, !dbg !17
+  }
+
+  !llvm.dbg.cu = !{!0}
+  !llvm.module.flags = !{!7, !8, !9, !10}
+  !llvm.ident = !{!11}
+  !0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 10.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, globals: !3, debugInfoForProfiling: true, nameTableKind: None)
+  !1 = !DIFile(filename: "main.cpp", directory: "F:\")
+  !2 = !{}
+  !3 = !{!4}
+  !4 = !DIGlobalVariableExpression(var: !5, expr: !DIExpression())
+  !5 = distinct !DIGlobalVariable(name: "start", scope: !0, file: !1, line: 4, type: !6, isLocal: false, isDefinition: true)
+  !6 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+  !7 = !{i32 2, !"Dwarf Version", i32 4}
+  !8 = !{i32 2, !"Debug Info Version", i32 3}
+  !9 = !{i32 1, !"wchar_size", i32 2}
+  !10 = !{i32 7, !"PIC Level", i32 2}
+  !11 = !{!"clang version 10.0.0"}
+  !12 = distinct !DISubprogram(name: "bb_to_bb", linkageName: "bb_to_bb", scope: !1, file: !1, line: 6, type: !13, scopeLine: 6, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !15)
+  !13 = !DISubroutineType(types: !14)
+  !14 = !{!6, !6}
+  !15 = !{!16}
+  !16 = !DILocalVariable(name: "myVar", scope: !12, file: !1, line: 7, type: !6)
+  !17 = !DILocation(line: 10, scope: !12)
+
+...
+---
+name: chiasm
+tracksRegLiveness: true
+liveins:
+  - { reg: '$rdi', virtual-reg: '' }
+stack:
+  - { id: 0, name: '', type: spill-slot, offset: -8, size: 8, alignment: 8,
+      stack-id: default, callee-saved-register: '', callee-saved-restored: true,
+      debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+body:  |
+  bb.0.entry:
+  liveins: $rdi, $rsi
+
+  bb.1:
+  liveins: $rsi, $rdi
+    CMP64ri8 renamable $rdi, 1, implicit-def $eflags, debug-location !17
+    JCC_1 %bb.17, 4, implicit $eflags, debug-location !17
+
+  bb.2:
+  liveins: $rsi, $rdi
+    DBG_VALUE $rsi, $noreg, !16, !DIExpression(), debug-location !17
+    CMP64ri8 renamable $rdi, 2, implicit-def $eflags, debug-location !17
+    JCC_1 %bb.16, 4, implicit $eflags, debug-location !17
+
+  bb.3:
+  liveins: $rsi, $rdi
+    CMP64ri8 renamable $rdi, 3, implicit-def $eflags, debug-location !17
+    JCC_1 %bb.15, 4, implicit $eflags, debug-location !17
+
+  bb.4:
+  liveins: $rsi, $rdi
+    CMP64ri8 renamable $rdi, 4, implicit-def $eflags, debug-location !17
+    JCC_1 %bb.14, 4, implicit $eflags, debug-location !17
+
+  bb.5:
+  liveins: $rsi, $rdi
+    DBG_VALUE $rsi, $noreg, !16, !DIExpression(), debug-location !17
+    CMP64ri8 renamable $rdi, 4, implicit-def $eflags, debug-location !17
+    JCC_1 %bb.13, 4, implicit $eflags, debug-location !17
+
+  bb.6:
+  liveins: $rsi, $rdi
+    CMP64ri8 renamable $rdi, 4, implicit-def $eflags, debug-location !17
+    JCC_1 %bb.12, 4, implicit $eflags, debug-location !17
+
+  bb.7:
+  liveins: $rsi, $rdi
+    CMP64ri8 renamable $rdi, 4, implicit-def $eflags, debug-location !17
+    JCC_1 %bb.11, 4, implicit $eflags, debug-location !17
+
+  bb.8:
+  liveins: $rsi, $rdi
+    CMP64ri8 renamable $rdi, 4, implicit-def $eflags, debug-location !17
+    JCC_1 %bb.10, 4, implicit $eflags, debug-location !17
+
+  bb.9:
+  liveins: $rsi, $rdi, $eflags
+    ;$rsi = MOV64ri 0, debug-location !17
+    ;JMP_1 %bb.1, debug-location !17
+
+  bb.10:
+  liveins: $rsi, $rdi, $eflags
+    JCC_1 %bb.8, 4, implicit $eflags, debug-location !17
+    
+  bb.11:
+  liveins: $rsi, $rdi, $eflags
+    JCC_1 %bb.7, 4, implicit $eflags, debug-location !17
+ 
+  bb.12:
+  liveins: $rsi, $rdi, $eflags
+    JCC_1 %bb.6, 4, implicit $eflags, debug-location !17
+ 
+  bb.13:
+  liveins: $rsi, $rdi, $eflags
+    JCC_1 %bb.5, 4, implicit $eflags, debug-location !17
+ 
+  bb.14:
+  liveins: $rsi, $rdi, $eflags
+    $rsi = MOV64ri 0, debug-location !17
+    JCC_1 %bb.4, 4, implicit $eflags, debug-location !17
+
+  bb.15:
+  liveins: $rsi, $rdi, $eflags
+    JCC_1 %bb.3, 4, implicit $eflags, debug-location !17
+
+  bb.16:
+  liveins: $rsi, $rdi, $eflags
+    JCC_1 %bb.2, 4, implicit $eflags, debug-location !17
+
+  bb.17:
+  liveins: $rsi, $rdi, $eflags
+    JCC_1 %bb.1, 4, implicit $eflags, debug-location !17
+ 
+  bb.18:
+  liveins: $rsi, $rdi, $eflags
+    RETQ
+
+...