[DwarfDebug] Don't merge DebugLocEntries if their pieces overlap

[loladiro]

Summary

Later in DWARF emission we check that DebugLocEntries have
non-overlapping pieces, so we should create any such entries
by merging here.

Fixes PR26163.

[loladiro]

clang-format (sorry forgot)

[aprantl]

Thanks!

lib/CodeGen/AsmPrinter/DwarfDebug.cpp

808 ↗

(On Diff #45058)

Please move the function to the cpp in a separate NFC commit. It helps with bisection and git blame.

817 ↗

(On Diff #45058)

This appears to be reasonable to me.

test/DebugInfo/ARM/PR26163.ll

7 ↗

(On Diff #45058)

Sad but true.

[aprantl]

test/DebugInfo/ARM/PR26163.ll

73 ↗

(On Diff #45058)

Can you remove all the unnecessary attributes? Usually that's all of them.

[dim]

Note: please consider that this should be merged to the 3.8 branch (with rL257977 probably).

[loladiro]

In D16249#328466, @dim wrote:

Note: please consider that this should be merged to the 3.8 branch (with rL257977 probably).

Yep, I requested as much from the release owner.

llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

 /// \brief If this and Next are describing different pieces of the same
 /// variable, merge them by appending Next's values to the current
 /// list of values.
 /// Return true if the merge was successful.
 bool DebugLocEntry::MergeValues(const DebugLocEntry &Next) {
   if (Begin == Next.Begin) {
     auto *Expr = cast_or_null<DIExpression>(Values[0].Expression);
     auto *NextExpr = cast_or_null<DIExpression>(Next.Values[0].Expression);
-    if (Expr->isBitPiece() && NextExpr->isBitPiece()) {
+    if (Expr->isBitPiece() && NextExpr->isBitPiece() &&
+        !piecesOverlap(Expr, NextExpr)) {
       addValues(Next.Values);
       End = Next.End;
       return true;
     }
   }
   return false;
 }
 

llvm/trunk/test/DebugInfo/ARM/PR26163.ll

+; RUN: llc -filetype=obj -o - < %s | llvm-dwarfdump - | FileCheck %s
+;
+; Checks that we're creating two ranges, one that terminates immediately
+; and one that spans the rest of the function. This isn't necessarily the
+; best thing to do here (and also not necessarily correct, since the first
+; one has a bit_piece), but it is what is currently being emitted, any
+; change here needs to be intentional, so the test is very specific.
+;
+; CHECK: .debug_loc contents:
+; CHECK: 0x00000000: Beginning address offset: 0x0000000000000004
+; CHECK:                Ending address offset: 0x0000000000000004
+; CHECK:                 Location description: 10 00 9f
+; CHECK:             Beginning address offset: 0x0000000000000004
+; CHECK:                Ending address offset: 0x0000000000000014
+; CHECK:                 Location description: 10 00 9f
+
+; Created form the following test case (PR26163) with
+; clang -cc1 -triple armv4t--freebsd11.0-gnueabi -emit-obj -debug-info-kind=standalone -O2 -x c test.c
+;
+; typedef unsigned int  size_t;
+; struct timeval {
+;   long long tv_sec;
+;   int tv_usec;
+; };
+; 
+; void *memset(void *, int, size_t);
+; void foo(void);
+; 
+; static void
+; bar(int value)
+; {
+;   struct timeval lifetime;
+; 
+;   memset(&lifetime, 0, sizeof(struct timeval));
+;   lifetime.tv_sec = value;
+; 
+;   foo();
+; }
+; 
+; int
+; parse_config_file(void)
+; {
+;   int value;
+; 
+;   bar(value);
+;   return (0);
+; }
+
+target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
+target triple = "armv4t--freebsd11.0-gnueabi"
+
+%struct.timeval = type { i64, i32 }
+
+declare void @llvm.dbg.declare(metadata, metadata, metadata)
+declare void @llvm.dbg.value(metadata, i64, metadata, metadata)
+
+declare void @foo()
+
+define i32 @parse_config_file() !dbg !4 {
+entry:
+  tail call void @llvm.dbg.value(metadata i32 0, i64 0, metadata !15, metadata !26), !dbg !27
+  tail call void @llvm.dbg.declare(metadata %struct.timeval* undef, metadata !16, metadata !26), !dbg !29
+  tail call void @llvm.dbg.value(metadata i64 0, i64 0, metadata !16, metadata !30), !dbg !29
+  tail call void @llvm.dbg.value(metadata i32 0, i64 0, metadata !16, metadata !31), !dbg !29
+  tail call void @foo() #3, !dbg !32
+  ret i32 0, !dbg !33
+}
+
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!22, !23, !24}
+!llvm.ident = !{!25}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 3.9.0 (https://github.com/llvm-mirror/clang 89dda3855cda574f355e6defa1d77bdae5053994) (llvm/trunk 257891)", isOptimized: true, runtimeVersion: 0, emissionKind: 1, enums: !2, subprograms: !3)
+!1 = !DIFile(filename: "<stdin>", directory: "/home/ubuntu/bugs")
+!2 = !{}
+!3 = !{!4, !11}
+!4 = distinct !DISubprogram(name: "parse_config_file", scope: !5, file: !5, line: 22, type: !6, isLocal: false, isDefinition: true, scopeLine: 23, flags: DIFlagPrototyped, isOptimized: true, variables: !9)
+!5 = !DIFile(filename: "test.c", directory: "/home/ubuntu/bugs")
+!6 = !DISubroutineType(types: !7)
+!7 = !{!8}
+!8 = !DIBasicType(name: "int", size: 32, align: 32, encoding: DW_ATE_signed)
+!9 = !{!10}
+!10 = !DILocalVariable(name: "value", scope: !4, file: !5, line: 24, type: !8)
+!11 = distinct !DISubprogram(name: "bar", scope: !5, file: !5, line: 11, type: !12, isLocal: true, isDefinition: true, scopeLine: 12, flags: DIFlagPrototyped, isOptimized: true, variables: !14)
+!12 = !DISubroutineType(types: !13)
+!13 = !{null, !8}
+!14 = !{!15, !16}
+!15 = !DILocalVariable(name: "value", arg: 1, scope: !11, file: !5, line: 11, type: !8)
+!16 = !DILocalVariable(name: "lifetime", scope: !11, file: !5, line: 13, type: !17)
+!17 = !DICompositeType(tag: DW_TAG_structure_type, name: "timeval", file: !5, line: 2, size: 128, align: 64, elements: !18)
+!18 = !{!19, !21}
+!19 = !DIDerivedType(tag: DW_TAG_member, name: "tv_sec", scope: !17, file: !5, line: 3, baseType: !20, size: 64, align: 64)
+!20 = !DIBasicType(name: "long long int", size: 64, align: 64, encoding: DW_ATE_signed)
+!21 = !DIDerivedType(tag: DW_TAG_member, name: "tv_usec", scope: !17, file: !5, line: 4, baseType: !8, size: 32, align: 32, offset: 64)
+!22 = !{i32 2, !"Debug Info Version", i32 3}
+!23 = !{i32 1, !"wchar_size", i32 4}
+!24 = !{i32 1, !"min_enum_size", i32 4}
+!25 = !{!"clang version 3.9.0 (https://github.com/llvm-mirror/clang 89dda3855cda574f355e6defa1d77bdae5053994) (llvm/trunk 257891)"}
+!26 = !DIExpression()
+!27 = !DILocation(line: 11, scope: !11, inlinedAt: !28)
+!28 = distinct !DILocation(line: 26, scope: !4)
+!29 = !DILocation(line: 13, scope: !11, inlinedAt: !28)
+!30 = !DIExpression(DW_OP_bit_piece, 0, 64)
+!31 = !DIExpression(DW_OP_bit_piece, 0, 32)
+!32 = !DILocation(line: 18, scope: !11, inlinedAt: !28)
+!33 = !DILocation(line: 27, scope: !4)