[DebugInfo] Test that LiveDebugVariables un-coalesces ranges over block boundaries

[jmorse]

Summary

LiveDebugVariables can coalesce ranges of variable locations across multiple basic blocks. However when it recreates DBG_VALUE instructions, it has to recreate one DBG_VALUE per block, otherwise it doesn't represent the pre-regalloc layout and variable assignments can go missing.

This feature works -- however while mucking around with LiveDebugVariables, I commented it out (the loop here [0]) and no tests failed. Thus, here's a test that checks LiveDebugVariables preserves DBG_VALUEs across block boundaries.

[0] https://github.com/llvm/llvm-project/blob/0c476111317cb7aaa9a3e9f75e1c35f83122ee26/llvm/lib/CodeGen/LiveDebugVariables.cpp#L1358

[aprantl]

test/DebugInfo/MIR/X86/livedebugvariables-crossbb-interval.mir

3

Nitpick: this isn't consistent with either name :-)

#define DEBUG_TYPE "livedebugvars"

static cl::opt<bool>
EnableLDV("live-debug-variables", cl::init(true),

cl::desc("Enable the live debug variables pass"), cl::Hidden);

Also, we should probably unify those two...

test/DebugInfo/MIR/X86/livedebugvariables-crossbb-interval.mir

+# RUN: llc -start-after=phi-node-elimination -stop-after=virtregrewriter %s -mtriple=x86_64-unknown-unknown -o - | FileCheck %s
+#
+# Test that when a livedebugvariables interval crosses a basic block boundary,
+# DBG_VALUEs are created in each covered basic block. In the IR below, control
+# flow moves from the bottom upwards, and the DBG_VALUEs from the entry block
+# to bb.1 become a single range. Check that they're transformed back into two
+# DBG_VALUEs after regalloc.
+
+# These checks look at the entry and bb.1 blocks, and ensure that there is a
+# DBG_VALUE in each.
+
+# CHECK:       ![[VARNUM:[0-9]+]] = !DILocalVariable(name: "b",
+# CHECK-LABEL: name: bar
+# CHECK-LABEL: bb.0.entry:
+# CHECK:       DBG_VALUE $[[SOMEREG:[a-z]+]], $noreg, ![[VARNUM]], !DIExpression()
+# CHECK-NEXT:  JMP_1 %bb.3
+# CHECK-LABEL: bb.1.bb1:
+# CHECK:       DBG_VALUE $[[SOMEREG]], $noreg, ![[VARNUM]], !DIExpression()
+# CHECK-NEXT:  JMP_1 %bb.4
+
+--- |
+  ; ModuleID = 'tmp.ll'
+  source_filename = "tmp.ll"
+  target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+  
+  %struct.a = type { i32 }
+  
+  ; Function Attrs: nounwind ssp
+  define i32 @bar(%struct.a* nocapture %b, i32 %shoes) !dbg !4 {
+  entry:
+    tail call void @llvm.dbg.value(metadata i32 %shoes, metadata !9, metadata !DIExpression()), !dbg !16
+    %tmp1 = getelementptr inbounds %struct.a, %struct.a* %b, i64 0, i32 0, !dbg !17
+    br label %bb3
+  
+  bb1:                                              ; preds = %bb2
+    tail call void @llvm.dbg.value(metadata i32 %shoes, metadata !9, metadata !DIExpression()), !dbg !16
+    %add = add nsw i32 %tmp2, 1, !dbg !18
+    br label %exit
+  
+  bb2:                                              ; preds = %bb3
+    tail call void @llvm.dbg.value(metadata i32 %tmp2, metadata !14, metadata !DIExpression()), !dbg !17
+    %call = tail call i32 (...) @foo(i32 %tmp2), !dbg !19
+    br label %bb1
+  
+  bb3:                                              ; preds = %entry
+    %tmp2 = load i32, i32* %tmp1, align 4, !dbg !17
+    br label %bb2
+  
+  exit:                                             ; preds = %bb1
+    ret i32 %shoes, !dbg !18
+  }
+  
+  declare i32 @foo(...)
+  
+  ; Function Attrs: nounwind readnone speculatable willreturn
+  declare void @llvm.dbg.value(metadata, metadata, metadata)
+  
+  ; Function Attrs: nounwind
+  declare void @llvm.stackprotector(i8*, i8**)
+  
+  !llvm.dbg.cu = !{!0}
+  !llvm.module.flags = !{!3}
+  
+  !0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 2.9 (trunk 122997)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, retainedTypes: !2)
+  !1 = !DIFile(filename: "bar.c", directory: "/private/tmp")
+  !2 = !{}
+  !3 = !{i32 1, !"Debug Info Version", i32 3}
+  !4 = distinct !DISubprogram(name: "bar", scope: !1, file: !1, line: 5, type: !5, virtualIndex: 6, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !8)
+  !5 = !DISubroutineType(types: !6)
+  !6 = !{!7}
+  !7 = !DIBasicType(name: "int", size: 32, align: 32, encoding: DW_ATE_signed)
+  !8 = !{!9, !14}
+  !9 = !DILocalVariable(name: "b", arg: 1, scope: !4, file: !1, line: 5, type: !10)
+  !10 = !DIDerivedType(tag: DW_TAG_pointer_type, scope: !0, baseType: !11, size: 64, align: 64)
+  !11 = !DICompositeType(tag: DW_TAG_structure_type, name: "a", scope: !0, file: !1, line: 1, size: 32, align: 32, elements: !12)
+  !12 = !{!13}
+  !13 = !DIDerivedType(tag: DW_TAG_member, name: "c", scope: !1, file: !1, line: 2, baseType: !7, size: 32, align: 32)
+  !14 = !DILocalVariable(name: "x", scope: !15, file: !1, line: 6, type: !7)
+  !15 = distinct !DILexicalBlock(scope: !4, file: !1, line: 5, column: 22)
+  !16 = !DILocation(line: 5, column: 19, scope: !4)
+  !17 = !DILocation(line: 6, column: 14, scope: !15)
+  !18 = !DILocation(line: 8, column: 2, scope: !15)
+  !19 = !DILocation(line: 7, column: 2, scope: !15)
+
+...
+---
+name:            bar
+alignment:       4
+tracksRegLiveness: true
+registers:
+  - { id: 0, class: gr64 }
+  - { id: 1, class: gr32 }
+  - { id: 2, class: gr64 }
+  - { id: 3, class: gr64 }
+  - { id: 4, class: gr32 }
+  - { id: 5, class: gr32 }
+  - { id: 6, class: gr32 }
+  - { id: 7, class: gr32 }
+liveins:
+  - { reg: '$rdi', virtual-reg: '%2' }
+  - { reg: '$esi', virtual-reg: '%4' }
+frameInfo:
+  hasCalls:        true
+machineFunctionInfo: {}
+body:             |
+  bb.0.entry:
+    liveins: $rdi, $esi
+  
+    %4:gr32 = COPY $esi
+    %2:gr64 = COPY $rdi
+    %3:gr64 = COPY killed %2
+    %5:gr32 = COPY killed %4
+    DBG_VALUE %5, $noreg, !9, !DIExpression(), debug-location !16
+    JMP_1 %bb.3
+  
+  bb.1.bb1:
+    DBG_VALUE %5, $noreg, !9, !DIExpression(), debug-location !16
+    JMP_1 %bb.4
+  
+  bb.2.bb2:
+    DBG_VALUE %6, $noreg, !14, !DIExpression(), debug-location !17
+    ADJCALLSTACKDOWN64 0, 0, 0, implicit-def $rsp, implicit-def $eflags, implicit-def $ssp, implicit $rsp, implicit $ssp, debug-location !19
+    $edi = COPY %6, debug-location !19
+    $al = MOV8ri 0, debug-location !19
+    CALL64pcrel32 @foo, csr_64, implicit $rsp, implicit $ssp, implicit $al, implicit $edi, implicit-def $eax, debug-location !19
+    ADJCALLSTACKUP64 0, 0, implicit-def $rsp, implicit-def $eflags, implicit-def $ssp, implicit $rsp, implicit $ssp, debug-location !19
+    %7:gr32 = COPY $eax, debug-location !19
+    JMP_1 %bb.1
+  
+  bb.3.bb3:
+    %6:gr32 = MOV32rm %3, 1, $noreg, 0, $noreg, debug-location !17 :: (load 4 from %ir.tmp1)
+    JMP_1 %bb.2
+  
+  bb.4.exit:
+    $eax = COPY %5, debug-location !18
+    RETQ implicit $eax, debug-location !18
+
+...