[DebugInfo] Invalidate debug info in ReassociatePass::RewriteExprTree

Summary:
When Reassociate is rewriting an expression tree it may
reuse old binary expression nodes, for new expressions.
Whenever an expression node is reused, but with a non-trivial
change in the result, we need to invalidate any debug info
that is associated with the node.

If for example rewriting
  x = mul a, b
  y = mul c, x
into
  x = mul c, b
  y = mul a, x
we still get the same result for 'y', but 'x' is a new expression.
All debug info referring to 'x' must be invalidated (marked as
optimized out) since we no longer calculate the expected value.

As a side-effect this patch avoid (at least some) problems where
reassociate could end up creating IR with debug-use before def.
Earlier the dbg.value nodes where left untouched in the IR, while
the reused binary nodes where sinked to just before the root node
of the rewritten expression tree. See PR27273 for more info about
such problems.

Reviewers: dblaikie, aprantl, dexonsmith

Reviewed By: aprantl

Subscribers: JDevlieghere, llvm-commits

Tags: #debug-info

Differential Revision: https://reviews.llvm.org/D45975

llvm-svn: 330804

1 files changed, 79 insertions, 0 deletions

diff --git a/llvm/test/Transforms/Reassociate/reassociate_dbgvalue_discard.ll b/llvm/test/Transforms/Reassociate/reassociate_dbgvalue_discard.ll
new file mode 100644
index 00000000000..59f1d4890e6
--- /dev/null
+++ b/llvm/test/Transforms/Reassociate/reassociate_dbgvalue_discard.ll
@@ -0,0 +1,79 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -reassociate -S -o - | FileCheck %s
+
+; After reassociation m1 and m2 aren't calculated as m1=c*a and m2=c*b any longer.
+; So let's verify that the dbg.value nodes for m1 and m3 are invalidated.
+
+source_filename = "reassociate_dbgvalue_discard.c"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define dso_local i32 @test1(i32 %a, i32 %b, i32 %c, i32 %d) local_unnamed_addr #0 !dbg !7 {
+; CHECK-LABEL: @test1(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    call void @llvm.dbg.value(metadata i32 undef, metadata !16, metadata !DIExpression()), !dbg !20
+; CHECK-NEXT:    call void @llvm.dbg.value(metadata i32 undef, metadata !17, metadata !DIExpression()), !dbg !21
+; CHECK-NEXT:    [[M1:%.*]] = mul i32 [[D:%.*]], [[C:%.*]], !dbg !22
+; CHECK-NEXT:    [[M3:%.*]] = mul i32 [[M1]], [[A:%.*]], !dbg !23
+; CHECK-NEXT:    call void @llvm.dbg.value(metadata i32 [[M3]], metadata !18, metadata !DIExpression()), !dbg !24
+; CHECK-NEXT:    [[M2:%.*]] = mul i32 [[D]], [[C]], !dbg !25
+; CHECK-NEXT:    [[M4:%.*]] = mul i32 [[M2]], [[B:%.*]], !dbg !26
+; CHECK-NEXT:    call void @llvm.dbg.value(metadata i32 [[M4]], metadata !19, metadata !DIExpression()), !dbg !27
+; CHECK-NEXT:    [[RES:%.*]] = xor i32 [[M3]], [[M4]]
+; CHECK-NEXT:    ret i32 [[RES]], !dbg !28
+;
+entry:
+  %m1 = mul i32 %c, %a, !dbg !24
+  call void @llvm.dbg.value(metadata i32 %m1, metadata !16, metadata !DIExpression()), !dbg !25
+  %m2 = mul i32 %c, %b, !dbg !26
+  call void @llvm.dbg.value(metadata i32 %m2, metadata !17, metadata !DIExpression()), !dbg !27
+  %m3 = mul i32 %m1, %d, !dbg !28
+  call void @llvm.dbg.value(metadata i32 %m3, metadata !18, metadata !DIExpression()), !dbg !29
+  %m4 = mul i32 %m2, %d, !dbg !30
+  call void @llvm.dbg.value(metadata i32 %m4, metadata !19, metadata !DIExpression()), !dbg !31
+  %res = xor i32 %m3, %m4
+  ret i32 %res, !dbg !32
+}
+
+declare void @llvm.dbg.value(metadata, metadata, metadata) #1
+
+attributes #0 = { nounwind readnone uwtable }
+attributes #1 = { nounwind readnone speculatable }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 7.0.0 (trunk 330596) (llvm/trunk 330594)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "reassociate_dbgvalue_discard.c", directory: "")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 7.0.0 (trunk 330596) (llvm/trunk 330594)"}
+!7 = distinct !DISubprogram(name: "test1", scope: !1, file: !1, line: 3, type: !8, isLocal: false, isDefinition: true, scopeLine: 3, flags: DIFlagPrototyped, isOptimized: true, unit: !0, variables: !11)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!10, !10, !10, !10, !10}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !{!12, !13, !14, !15, !16, !17, !18, !19}
+!12 = !DILocalVariable(name: "a", arg: 1, scope: !7, file: !1, line: 3, type: !10)
+!13 = !DILocalVariable(name: "b", arg: 2, scope: !7, file: !1, line: 3, type: !10)
+!14 = !DILocalVariable(name: "c", arg: 3, scope: !7, file: !1, line: 3, type: !10)
+!15 = !DILocalVariable(name: "d", arg: 4, scope: !7, file: !1, line: 3, type: !10)
+!16 = !DILocalVariable(name: "t1", scope: !7, file: !1, line: 4, type: !10)
+!17 = !DILocalVariable(name: "t2", scope: !7, file: !1, line: 5, type: !10)
+!18 = !DILocalVariable(name: "t3", scope: !7, file: !1, line: 6, type: !10)
+!19 = !DILocalVariable(name: "t4", scope: !7, file: !1, line: 7, type: !10)
+!20 = !DILocation(line: 3, column: 15, scope: !7)
+!21 = !DILocation(line: 3, column: 22, scope: !7)
+!22 = !DILocation(line: 3, column: 29, scope: !7)
+!23 = !DILocation(line: 3, column: 36, scope: !7)
+!24 = !DILocation(line: 4, column: 14, scope: !7)
+!25 = !DILocation(line: 4, column: 7, scope: !7)
+!26 = !DILocation(line: 5, column: 14, scope: !7)
+!27 = !DILocation(line: 5, column: 7, scope: !7)
+!28 = !DILocation(line: 6, column: 15, scope: !7)
+!29 = !DILocation(line: 6, column: 7, scope: !7)
+!30 = !DILocation(line: 7, column: 15, scope: !7)
+!31 = !DILocation(line: 7, column: 7, scope: !7)
+!32 = !DILocation(line: 8, column: 3, scope: !7)