[PATCH] D26769: [IR] Remove the DIExpression field from DIGlobalVariable.

[Adrian Prantl via llvm-commits]

aprantl created this revision.
aprantl added reviewers: dexonsmith, dblaikie, pcc.
aprantl added a subscriber: llvm-commits.
aprantl set the repository for this revision to rL LLVM.

This patch implements PR31013 by introducing a DIGlobalVariableExpression that holds a pair of DIGlobalVariable and DIExpression.

      

Currently, DIGlobalVariables holds a DIExpression. This is not the  best way to model this:

1. The DIGlobalVariable should describe the source level variable, not how to get to its location.
2. It makes it unsafe/hard to update the expressions when we call replaceExpression on the DIGLobalVariable.
3. It makes it impossible to represent a global variable that is in more than one location (e.g., a variable with multiple DW_OP_piece-s).  We also moved away from attaching the DIExpression to DILocalVariable for the same reasons.

A better representation would be to add a DIGlobalVariableExpression(var: !DIGlobalVariable(...), expr: !DIExpression(...)) that wraps a global variable and an expression. For example, let's say we have a global symbol g that doesn't need an expression — this would still be represented as:

  @g = global i32 0, !dbg !0
  !0 = DIGlobalVariable(name: "g", ...)

Later, after some transformation, this becomes:

  @opt_g = global i32 *, !dbg !1
  !0 = distinct !DIGlobalVariable(name: "g", ...) ; Identical to !0 above.
  !1 = !DIGlobalVariableExpr(var: !0, expr: !2)   ; Not distinct.
  !2 = !DIExpression(DW_OP_deref, ...)

This allows transformations to just add new mergeable metadata on top of the existing DIGlobalVariable without blowing up the representation if they aren't needed.
[reply] [-] Comment 1

For more discussion see https://llvm.org/bugs/show_bug.cgi?id=31013.


Repository:
  rL LLVM

https://reviews.llvm.org/D26769

Files:
  include/llvm/Bitcode/LLVMBitCodes.h
  include/llvm/IR/DIBuilder.h
  include/llvm/IR/DebugInfo.h
  include/llvm/IR/DebugInfoMetadata.h
  include/llvm/IR/GlobalVariable.h
  include/llvm/IR/Metadata.def
  lib/Analysis/ModuleDebugInfoPrinter.cpp
  lib/AsmParser/LLParser.cpp
  lib/Bitcode/Reader/BitcodeReader.cpp
  lib/Bitcode/Writer/BitcodeWriter.cpp
  lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
  lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
  lib/CodeGen/AsmPrinter/DwarfCompileUnit.h
  lib/CodeGen/AsmPrinter/DwarfDebug.cpp
  lib/IR/AsmWriter.cpp
  lib/IR/DIBuilder.cpp
  lib/IR/DebugInfo.cpp
  lib/IR/DebugInfoMetadata.cpp
  lib/IR/LLVMContextImpl.h
  lib/IR/Metadata.cpp
  lib/IR/Verifier.cpp
  lib/Transforms/IPO/StripSymbols.cpp
  lib/Transforms/Instrumentation/AddressSanitizer.cpp
  test/Assembler/diglobalvariable.ll
  test/Assembler/diglobalvariableexpression.ll
  test/Bitcode/DIGlobalVariableExpr.ll
  test/Bitcode/DIGlobalVariableExpr.ll.bc
  test/Bitcode/diglobalvariable-3.8.ll
  test/Bitcode/diglobalvariable-3.8.ll.bc
  test/DebugInfo/X86/multiple-at-const-val.ll
  test/DebugInfo/X86/pr12831.ll
  test/DebugInfo/X86/split-global.ll
  test/DebugInfo/X86/stack-value-dwarf4.ll
  test/DebugInfo/X86/unattached-global.ll
  test/Transforms/GlobalMerge/debug-info.ll
  unittests/IR/MetadataTest.cpp

-------------- next part --------------
A non-text attachment was scrubbed...
Name: D26769.78269.patch
Type: text/x-patch
Size: 71955 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20161116/6e0286b4/attachment-0001.bin>