[PATCH] D103162: [DebugInfo] Limit the number of values that may be referenced by a dbg.value

Wed May 26 09:34:29 PDT 2021

This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
Closed by commit rGa0bd6105d806: [DebugInfo] Limit the number of values that may be referenced by a dbg.value (authored by StephenTozer).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D103162/new/

https://reviews.llvm.org/D103162

Files:
  llvm/lib/Transforms/Utils/Local.cpp
  llvm/test/DebugInfo/limit-arglist-size.ll


Index: llvm/test/DebugInfo/limit-arglist-size.ll
===================================================================

--- /dev/null
+++ llvm/test/DebugInfo/limit-arglist-size.ll
@@ -0,0 +1,63 @@
+; RUN: opt -S -instcombine %s -o - | FileCheck %s
+
+; For performance reasons, we currently limit the number of values that can be
+; referenced by a dbg.value to 16. This test checks that we do not exceed this
+; limit during salvaging.
+
+; CHECK: DIArgList(i32 undef
+; CHECK-NOT: DW_OP_LLVM_arg, 16
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define i32 @_Z3foov() local_unnamed_addr !dbg !9 {
+entry:
+  %call = call i32 @_Z3barv(), !dbg !14
+  %call1 = call i32 @_Z3barv(), !dbg !14
+  %add = add nsw i32 %call, %call1, !dbg !14
+  %call2 = call i32 @_Z3barv(), !dbg !14
+  %call4 = call i32 @_Z3barv(), !dbg !14
+  %call6 = call i32 @_Z3barv(), !dbg !14
+  %call8 = call i32 @_Z3barv(), !dbg !14
+  %call10 = call i32 @_Z3barv(), !dbg !14
+  %call12 = call i32 @_Z3barv(), !dbg !14
+  %call14 = call i32 @_Z3barv(), !dbg !14
+  %call16 = call i32 @_Z3barv(), !dbg !14
+  %call18 = call i32 @_Z3barv(), !dbg !14
+  %call20 = call i32 @_Z3barv(), !dbg !14
+  %call22 = call i32 @_Z3barv(), !dbg !14
+  %call24 = call i32 @_Z3barv(), !dbg !14
+  %call26 = call i32 @_Z3barv(), !dbg !14
+  %call28 = call i32 @_Z3barv(), !dbg !14
+  %call30 = call i32 @_Z3barv(), !dbg !14
+  call void @llvm.dbg.value(metadata !DIArgList(i32 %add, i32 %call30, i32 %call28, i32 %call26, i32 %call24, i32 %call22, i32 %call20, i32 %call18, i32 %call16, i32 %call14, i32 %call12, i32 %call10, i32 %call8, i32 %call6, i32 %call4, i32 %call2), metadata !15, metadata !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_LLVM_arg, 15, DW_OP_plus, DW_OP_LLVM_arg, 14, DW_OP_plus, DW_OP_LLVM_arg, 13, DW_OP_plus, DW_OP_LLVM_arg, 12, DW_OP_plus, DW_OP_LLVM_arg, 11, DW_OP_plus, DW_OP_LLVM_arg, 10, DW_OP_plus, DW_OP_LLVM_arg, 9, DW_OP_plus, DW_OP_LLVM_arg, 8, DW_OP_plus, DW_OP_LLVM_arg, 7, DW_OP_plus, DW_OP_LLVM_arg, 6, DW_OP_plus, DW_OP_LLVM_arg, 5, DW_OP_plus, DW_OP_LLVM_arg, 4, DW_OP_plus, DW_OP_LLVM_arg, 3, DW_OP_plus, DW_OP_LLVM_arg, 2, DW_OP_plus, DW_OP_LLVM_arg, 1, DW_OP_plus, DW_OP_stack_value)), !dbg !16
+  %call32 = call i32 @_Z3barv(), !dbg !17
+  ret i32 %call32, !dbg !17
+}
+
+declare dso_local i32 @_Z3barv() local_unnamed_addr
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5, !6, !7}
+!llvm.ident = !{!8}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 13.0.0", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "limit-arglist-size.cpp", directory: "/")
+!2 = !{}
+!3 = !{i32 7, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{i32 7, !"uwtable", i32 1}
+!7 = !{i32 7, !"frame-pointer", i32 2}
+!8 = !{!"clang version 13.0.0"}
+!9 = distinct !DISubprogram(name: "foo", linkageName: "_Z3foov", scope: !10, file: !10, line: 3, type: !11, scopeLine: 3, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !2)
+!10 = !DIFile(filename: "./limit-arglist-size.cpp", directory: "/")
+!11 = !DISubroutineType(types: !12)
+!12 = !{!13}
+!13 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!14 = !DILocation(line: 4, scope: !9)
+!15 = !DILocalVariable(name: "v16", scope: !9, file: !10, line: 4, type: !13)
+!16 = !DILocation(line: 0, scope: !9)
+!17 = !DILocation(line: 5, scope: !9)
Index: llvm/lib/Transforms/Utils/Local.cpp
===================================================================
--- llvm/lib/Transforms/Utils/Local.cpp
+++ llvm/lib/Transforms/Utils/Local.cpp
@@ -1724,6 +1724,9 @@
 
 void llvm::salvageDebugInfoForDbgValues(
     Instruction &I, ArrayRef<DbgVariableIntrinsic *> DbgUsers) {
+  // This is an arbitrary chosen limit on the maximum number of values we can
+  // salvage up to in a DIArgList, used for performance reasons.
+  const unsigned MaxDebugArgs = 16;
   bool Salvaged = false;
 
   for (auto *DII : DbgUsers) {
@@ -1748,11 +1751,15 @@
     DII->replaceVariableLocationOp(&I, I.getOperand(0));
     if (AdditionalValues.empty()) {
       DII->setExpression(SalvagedExpr);
-    } else if (isa<DbgValueInst>(DII)) {
+    } else if (isa<DbgValueInst>(DII) &&
+               DII->getNumVariableLocationOps() + AdditionalValues.size() <=
+                   MaxDebugArgs) {
       DII->addVariableLocationOps(AdditionalValues, SalvagedExpr);
     } else {
       // Do not salvage using DIArgList for dbg.addr/dbg.declare, as it is
       // currently only valid for stack value expressions.
+      // Also do not salvage if the resulting DIArgList would contain an
+      // unreasonably large number of values.
       Value *Undef = UndefValue::get(I.getOperand(0)->getType());
       DII->replaceVariableLocationOp(I.getOperand(0), Undef);
     }


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