test/DebugInfo/MIR/InstrRef/single-assign-propagation.mir

# RUN: llc %s -march=x86-64 -run-pass=livedebugvalues -o - \
# RUN:       -experimental-debug-variable-locations=true \
# RUN:     | FileCheck %s -implicit-check-not=DBG_VALUE \
# RUN:        --check-prefixes=CHECK,COMMON
# RUN: llc %s -march=x86-64 -run-pass=livedebugvalues -o - \
# RUN:       -experimental-debug-variable-locations=false \
# RUN:     | FileCheck %s -implicit-check-not=DBG_VALUE \
# RUN:        --check-prefixes=VARLOC,COMMON
#
# This test is designed to stimulate a simplification of variable-value
# propagation in InstrRefBasedLDV. When we only have a single assignment of
# a variable, we don't have to completely enumerate all the PHIs the variable
# has and then value propagate through them: the variable value is available
# only in those blocks dominated by the assignment. Example in this test:
#
#             entry
#            /  |  \
#           /   v   \
#          /   bb1   \    <--- Single variable assignment happens here
#         /   /   \   \
#        /   v     v   \
#        | bb2     bb3 |
#        |   \    /    |
#        |    v  v     |
#        |     bb4     |
#         \   /   \    /
#          v v     v  v
#           bb5    bb6    <---  Dominance frontier is here
#
# The general InstrRefBasedLDV algorithm takes this CFG, places PHIs at bb5 and
# bb6, then value-propagates until it's determined that they can't be
# eliminated. Then, we determine that there's no machine location for such PHIs,
# and no variable location is emitted.
#
# The fast way of doing this: observe that the variable value can never extend
# past the dominance frontier of the block where the assignment happens. So
# just propagate the variable value into the dominated blocks, and avoid the
# general algorithm.
#
# Doing so introduces a functional change: VarLocBasedLDV won't propagate
# variable locations through out-of-scope blocks, and InstrRefBasedLDV tries to
# replicate VarLocBasedLDV most of the time. In the MIR below, bb2 is out of
# scope. This effectively becomes another variable assignment (of undef), which
# requires full SSA and value propagation to emulate what VarLocBasedLDV did.
# Applying this speed optimisation makes us diverge from what VarLocBasedLDV
# does by not treating the out-of-scope block as an effective undef assignment,
# hence this test.
#
# CHECK-LABEL: bb.1:
# CHECK:       DBG_VALUE
# CHECK-LABEL: bb.2:
## No location here because it's out-of-scope.
# CHECK-LABEL: bb.3:
# CHECK:       DBG_VALUE
# CHECK-LABEL: bb.4:
# CHECK:       DBG_VALUE
#
## VarLocBasedLDV will take the DBG_VALUE in the assignment block, propagate
## to bb.3, but not into bb.4 because of the intervening out-of-scope block.
#
# VARLOC-LABEL: bb.1:
# VARLOC:       DBG_VALUE
# VARLOC-LABEL: bb.2:
## No location here because it's out-of-scope.
# VARLOC-LABEL: bb.3:
# VARLOC:       DBG_VALUE
#
## Common tail for 'test2' -- this is checking that the assignment of undef or
## $noreg in single-assignment mode doesn't lead to trouble further down the
## line, specifically assertion failures.
#
# COMMON-LABEL: name: test2
# COMMON: DBG_VALUE $noreg
--- |
  define i32 @_Z8bb_to_bb() local_unnamed_addr !dbg !12 {
  entry:
    ret i32 0, !dbg !17
  }

  define i32 @test2() local_unnamed_addr !dbg !112 {
  entry:
    ret i32 0, !dbg !117
  }

  !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", 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"}
  !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: !18, file: !1, line: 7, type: !6)
  !17 = !DILocation(line: 10, scope: !18)
  !18 = distinct !DILexicalBlock(scope: !12, file: !1, line: 1, column: 1)
  !19 = distinct !DILexicalBlock(scope: !12, file: !1, line: 1, column: 1)
  !20 = !DILocation(line: 10, scope: !19)
  !112 = distinct !DISubprogram(name: "test2", linkageName: "102", scope: !1, file: !1, line: 6, type: !13, scopeLine: 6, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !115)
  !115 = !{!116}
  !116 = !DILocalVariable(name: "myVar", scope: !118, file: !1, line: 7, type: !6)
  !117 = !DILocation(line: 10, scope: !118)
  !118 = distinct !DILexicalBlock(scope: !112, file: !1, line: 1, column: 1)
  !119 = distinct !DILexicalBlock(scope: !112, file: !1, line: 1, column: 1)
  !120 = !DILocation(line: 10, scope: !119)

...
---
name: _Z8bb_to_bb
debugValueSubstitutions:
  - { srcinst: 4, srcop: 0, dstinst: 3, dstop: 0, subreg: 0 }
body:  |
  bb.0.entry:
    successors: %bb.1, %bb.5, %bb.6

    $rax = MOV64ri 1, debug-instr-number 1, debug-location !17
    JCC_1 %bb.5, 1, implicit $eflags
    JCC_1 %bb.6, 2, implicit $eflags
    JMP_1 %bb.1

  bb.1:
    successors: %bb.2, %bb.3

    DBG_VALUE $rax, $noreg, !16, !DIExpression(), debug-location !17
    JCC_1 %bb.3, 1, implicit $eflags, debug-location !17

  bb.2:
    successors: %bb.4

    JMP_1 %bb.4, debug-location !20

  bb.3:
    successors: %bb.4

    JMP_1 %bb.4, debug-location !17

  bb.4:
    successors: %bb.5, %bb.6

    JCC_1 %bb.5, 1, implicit $eflags, debug-location !17
    JMP_1 %bb.6, debug-location !17

  bb.5:
    RET 0, debug-location !17

  bb.6:
    RET 0, debug-location !17
...
---
name: test2
debugValueSubstitutions:
  - { srcinst: 4, srcop: 0, dstinst: 3, dstop: 0, subreg: 0 }
body:  |
  bb.0.entry:
    successors: %bb.1, %bb.5, %bb.6

    $rax = MOV64ri 1, debug-instr-number 1, debug-location !117
    JCC_1 %bb.5, 1, implicit $eflags
    JCC_1 %bb.6, 2, implicit $eflags
    JMP_1 %bb.1

  bb.1:
    successors: %bb.2, %bb.3

    DBG_VALUE $noreg, $noreg, !116, !DIExpression(), debug-location !117
    JCC_1 %bb.3, 1, implicit $eflags, debug-location !117

  bb.2:
    successors: %bb.4

    JMP_1 %bb.4, debug-location !120

  bb.3:
    successors: %bb.4

    JMP_1 %bb.4, debug-location !117

  bb.4:
    successors: %bb.5, %bb.6

    JCC_1 %bb.5, 1, implicit $eflags, debug-location !117
    JMP_1 %bb.6, debug-location !117

  bb.5:
    RET 0, debug-location !117

  bb.6:
    RET 0, debug-location !117