[PATCH] D101373: [DebugInfo] Drop DBG_VALUE_LISTs with an excessive number of debug operands
Stephen Tozer via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Tue Apr 27 15:25:02 PDT 2021
StephenTozer updated this revision to Diff 341000.
StephenTozer added a comment.
Simplify test case by using constants in the DIArgList instead of SSA values.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D101373/new/
https://reviews.llvm.org/D101373
Files:
llvm/lib/CodeGen/LiveDebugVariables.cpp
llvm/test/DebugInfo/X86/live-debug-vars-loc-limit.ll
Index: llvm/test/DebugInfo/X86/live-debug-vars-loc-limit.ll
===================================================================
--- /dev/null
+++ llvm/test/DebugInfo/X86/live-debug-vars-loc-limit.ll
@@ -0,0 +1,43 @@
+; RUN: llc --stop-after=virtregrewriter -o - %s | FileCheck %s
+
+; Check that any debug value with 64+ unique machine location operands is set
+; undef by LiveDebugVariables.
+
+; CHECK: ![[VAR_A:[0-9]+]] = !DILocalVariable(name: "a"
+
+; CHECK-NOT: DBG_VALUE
+; CHECK: DBG_VALUE_LIST ![[VAR_A]], !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_stack_value), $noreg
+; CHECK-NOT: DBG_VALUE
+
+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 dso_local i32 @_Z3fooi(i32 returned %b) local_unnamed_addr !dbg !8 {
+entry:
+ call void @llvm.dbg.value(metadata !DIArgList(i32 1, i32 126, i32 124, i32 122, i32 120, i32 118, i32 116, i32 114, i32 112, i32 110, i32 108, i32 106, i32 104, i32 102, i32 100, i32 98, i32 96, i32 94, i32 92, i32 90, i32 88, i32 86, i32 84, i32 82, i32 80, i32 78, i32 76, i32 74, i32 72, i32 70, i32 68, i32 66, i32 64, i32 62, i32 60, i32 58, i32 56, i32 54, i32 52, i32 50, i32 48, i32 46, i32 44, i32 42, i32 40, i32 38, i32 36, i32 34, i32 32, i32 30, i32 28, i32 26, i32 24, i32 22, i32 20, i32 18, i32 16, i32 14, i32 12, i32 10, i32 8, i32 6, i32 4, i32 2), metadata !14, metadata !DIExpression(DW_OP_LLVM_arg, 0, DW_OP_LLVM_arg, 63, DW_OP_plus, DW_OP_LLVM_arg, 62, DW_OP_plus, DW_OP_LLVM_arg, 61, DW_OP_plus, DW_OP_LLVM_arg, 60, DW_OP_plus, DW_OP_LLVM_arg, 59, DW_OP_plus, DW_OP_LLVM_arg, 58, DW_OP_plus, DW_OP_LLVM_arg, 57, DW_OP_plus, DW_OP_LLVM_arg, 56, DW_OP_plus, DW_OP_LLVM_arg, 55, DW_OP_plus, DW_OP_LLVM_arg, 54, DW_OP_plus, DW_OP_LLVM_arg, 53, DW_OP_plus, DW_OP_LLVM_arg, 52, DW_OP_plus, DW_OP_LLVM_arg, 51, DW_OP_plus, DW_OP_LLVM_arg, 50, DW_OP_plus, DW_OP_LLVM_arg, 49, DW_OP_plus, DW_OP_LLVM_arg, 48, DW_OP_plus, DW_OP_LLVM_arg, 47, DW_OP_plus, DW_OP_LLVM_arg, 46, DW_OP_plus, DW_OP_LLVM_arg, 45, DW_OP_plus, DW_OP_LLVM_arg, 44, DW_OP_plus, DW_OP_LLVM_arg, 43, DW_OP_plus, DW_OP_LLVM_arg, 42, DW_OP_plus, DW_OP_LLVM_arg, 41, DW_OP_plus, DW_OP_LLVM_arg, 40, DW_OP_plus, DW_OP_LLVM_arg, 39, DW_OP_plus, DW_OP_LLVM_arg, 38, DW_OP_plus, DW_OP_LLVM_arg, 37, DW_OP_plus, DW_OP_LLVM_arg, 36, DW_OP_plus, DW_OP_LLVM_arg, 35, DW_OP_plus, DW_OP_LLVM_arg, 34, DW_OP_plus, DW_OP_LLVM_arg, 33, DW_OP_plus, DW_OP_LLVM_arg, 32, DW_OP_plus, DW_OP_LLVM_arg, 31, DW_OP_plus, DW_OP_LLVM_arg, 30, DW_OP_plus, DW_OP_LLVM_arg, 29, DW_OP_plus, DW_OP_LLVM_arg, 28, DW_OP_plus, DW_OP_LLVM_arg, 27, DW_OP_plus, DW_OP_LLVM_arg, 26, DW_OP_plus, DW_OP_LLVM_arg, 25, DW_OP_plus, DW_OP_LLVM_arg, 24, DW_OP_plus, DW_OP_LLVM_arg, 23, DW_OP_plus, DW_OP_LLVM_arg, 22, DW_OP_plus, DW_OP_LLVM_arg, 21, DW_OP_plus, DW_OP_LLVM_arg, 20, DW_OP_plus, DW_OP_LLVM_arg, 19, DW_OP_plus, DW_OP_LLVM_arg, 18, DW_OP_plus, DW_OP_LLVM_arg, 17, DW_OP_plus, DW_OP_LLVM_arg, 16, DW_OP_plus, 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 !15
+ ret i32 %b, !dbg !16
+}
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5, !6}
+!llvm.ident = !{!7}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 13.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "live-debug-vars-loc-limit.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 = !{!"clang version 13.0.0"}
+!8 = distinct !DISubprogram(name: "foo", linkageName: "_Z3fooi", scope: !1, file: !1, line: 1, type: !9, scopeLine: 1, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !12)
+!9 = !DISubroutineType(types: !10)
+!10 = !{!11, !11}
+!11 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!12 = !{!13, !14}
+!13 = !DILocalVariable(name: "b", arg: 1, scope: !8, file: !1, line: 1, type: !11)
+!14 = !DILocalVariable(name: "a", scope: !8, file: !1, line: 2, type: !11)
+!15 = !DILocation(line: 0, scope: !8)
+!16 = !DILocation(line: 3, column: 3, scope: !8)
Index: llvm/lib/CodeGen/LiveDebugVariables.cpp
===================================================================
--- llvm/lib/CodeGen/LiveDebugVariables.cpp
+++ llvm/lib/CodeGen/LiveDebugVariables.cpp
@@ -119,17 +119,33 @@
DIExpression::replaceArg(Expression, OpIdx, DuplicatingIdx);
}
}
- // A debug value referencing 64+ unique machine locations is very likely
- // to be the result of a bug earlier in the pipeline. If by some means this
- // limit is validly reached, then we can add a byte to the size of
- // LocNoCount.
- assert(LocNoVec.size() < 64 &&
- "debug value containing 64+ unique machine locations is not "
- "supported by Live Debug Variables");
- LocNoCount = LocNoVec.size();
- if (LocNoCount > 0) {
- LocNos.reset(new unsigned[LocNoCount]());
- std::copy(LocNoVec.begin(), LocNoVec.end(), loc_nos_begin());
+ // FIXME: Debug values referencing 64+ unique machine locations are rare and
+ // currently unsupported for performance reasons. If we can verify that
+ // performance is acceptable for such debug values, we can increase the
+ // bit-width of LocNoCount to 14 to enable up to 16384 unique machine
+ // locations. We will also need to verify that this does not cause issues
+ // with LiveDebugVariables' use of IntervalMap.
+ if (LocNoVec.size() < 64) {
+ LocNoCount = LocNoVec.size();
+ if (LocNoCount > 0) {
+ LocNos = std::make_unique<unsigned[]>(LocNoCount);
+ std::copy(LocNoVec.begin(), LocNoVec.end(), loc_nos_begin());
+ }
+ } else {
+ LLVM_DEBUG(dbgs() << "Found debug value with 64+ unique machine "
+ "locations, dropping...\n");
+ LocNoCount = 1;
+ // Turn this into an undef debug value list; right now, the simplest form
+ // of this is an expression with one arg, and an undef debug operand.
+ Expression =
+ DIExpression::get(Expr.getContext(), {dwarf::DW_OP_LLVM_arg, 0,
+ dwarf::DW_OP_stack_value});
+ if (auto FragmentInfoOpt = Expr.getFragmentInfo())
+ Expression = *DIExpression::createFragmentExpression(
+ Expression, FragmentInfoOpt->OffsetInBits,
+ FragmentInfoOpt->SizeInBits);
+ LocNos = std::make_unique<unsigned[]>(LocNoCount);
+ LocNos[0] = UndefLocNo;
}
}
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