From d11155d273af00f75c2b40a5ca3007463f9808c1 Mon Sep 17 00:00:00 2001 From: Vedant Kumar Date: Wed, 27 May 2020 13:22:10 -0700 Subject: [PATCH] [LiveDebugValues] Add cutoffs to avoid pathological behavior Summary: We received a report of LiveDebugValues consuming 25GB+ of RAM when compiling code generated by Unity's IL2CPP scripting backend. There's an initial 5GB spike due to repeatedly copying cached lists of MachineBasicBlocks within the UserValueScopes members of VarLocs. But the larger scaling issue arises due to the fact that prior to range extension, there are 81K basic blocks and 156K DBG_VALUEs: given enough memory, LiveDebugValues would insert 101 million MIs (I counted this by incrementing a counter inside of VarLoc::BuildDbgValue). It seems like LiveDebugValues would have to be rearchitected to support this kind of input (we'd need some new represntation for DBG_VALUEs that get inserted into ~every block via flushPendingLocs). OTOH, large globs of auto-generated code are typically not debugged interactively. So: add cutoffs to disable range extension when the input is too big. I chose the cutoffs experimentally, erring on the conservative side. When compiling a large collection of Apple software, range extension never got disabled. rdar://63418929 Reviewers: aprantl, friss, jmorse, Orlando Subscribers: hiraditya, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D80662 --- llvm/lib/CodeGen/LiveDebugValues.cpp | 28 ++++++ .../MIR/X86/live-debug-values-cutoffs.mir | 99 ++++++++++++++++++++++ 2 files changed, 127 insertions(+) create mode 100644 llvm/test/DebugInfo/MIR/X86/live-debug-values-cutoffs.mir diff --git a/llvm/lib/CodeGen/LiveDebugValues.cpp b/llvm/lib/CodeGen/LiveDebugValues.cpp index 00a6149..2d11a23 100644 --- a/llvm/lib/CodeGen/LiveDebugValues.cpp +++ b/llvm/lib/CodeGen/LiveDebugValues.cpp @@ -81,6 +81,18 @@ using namespace llvm; STATISTIC(NumInserted, "Number of DBG_VALUE instructions inserted"); STATISTIC(NumRemoved, "Number of DBG_VALUE instructions removed"); +// Options to prevent pathological compile-time behavior. If InputBBLimit and +// InputDbgValueLimit are both exceeded, range extension is disabled. +static cl::opt InputBBLimit( + "livedebugvalues-input-bb-limit", + cl::desc("Maximum input basic blocks before DBG_VALUE limit applies"), + cl::init(10000), cl::Hidden); +static cl::opt InputDbgValueLimit( + "livedebugvalues-input-dbg-value-limit", + cl::desc( + "Maximum input DBG_VALUE insts supported by debug range extension"), + cl::init(50000), cl::Hidden); + // If @MI is a DBG_VALUE with debug value described by a defined // register, returns the number of this register. In the other case, returns 0. static Register isDbgValueDescribedByReg(const MachineInstr &MI) { @@ -1753,6 +1765,22 @@ bool LiveDebugValues::ExtendRanges(MachineFunction &MF) { Worklist.push(RPONumber); ++RPONumber; } + + if (RPONumber > InputBBLimit) { + unsigned NumInputDbgValues = 0; + for (auto &MBB : MF) + for (auto &MI : MBB) + if (MI.isDebugValue()) + ++NumInputDbgValues; + if (NumInputDbgValues > InputDbgValueLimit) { + LLVM_DEBUG(dbgs() << "Disabling LiveDebugValues: " << MF.getName() + << " has " << RPONumber << " basic blocks and " + << NumInputDbgValues + << " input DBG_VALUEs, exceeding limits.\n"); + return false; + } + } + // This is a standard "union of predecessor outs" dataflow problem. // To solve it, we perform join() and process() using the two worklist method // until the ranges converge. diff --git a/llvm/test/DebugInfo/MIR/X86/live-debug-values-cutoffs.mir b/llvm/test/DebugInfo/MIR/X86/live-debug-values-cutoffs.mir new file mode 100644 index 0000000..f14b746 --- /dev/null +++ b/llvm/test/DebugInfo/MIR/X86/live-debug-values-cutoffs.mir @@ -0,0 +1,99 @@ +# Test cutoffs for livedebugvalues debug range extension. +# Disable LDV if the input-bb-limit AND the input-dbg-value-limit are both exceeded. + +# RUN: llc %s -o - -run-pass=livedebugvalues -mtriple=x86_64-unknown-unknown \ +# RUN: -livedebugvalues-input-bb-limit=1 \ +# RUN: -livedebugvalues-input-dbg-value-limit=1 \ +# RUN: | FileCheck %s -check-prefix=LDV-DISABLED + +# RUN: llc %s -o - -run-pass=livedebugvalues -mtriple=x86_64-unknown-unknown \ +# RUN: -livedebugvalues-input-bb-limit=1 \ +# RUN: -livedebugvalues-input-dbg-value-limit=10 \ +# RUN: | FileCheck %s -check-prefix=LDV-ENABLED + +# RUN: llc %s -o - -run-pass=livedebugvalues -mtriple=x86_64-unknown-unknown \ +# RUN: -livedebugvalues-input-bb-limit=10 \ +# RUN: -livedebugvalues-input-dbg-value-limit=1 \ +# RUN: | FileCheck %s -check-prefix=LDV-ENABLED + +# RUN: llc %s -o - -run-pass=livedebugvalues -mtriple=x86_64-unknown-unknown \ +# RUN: -livedebugvalues-input-bb-limit=10 \ +# RUN: -livedebugvalues-input-dbg-value-limit=10 \ +# RUN: | FileCheck %s -check-prefix=LDV-ENABLED + +# LDV-DISABLED-LABEL: bb.1.exit +# LDV-DISABLED-NEXT: $edi = MOV32rm + +# LDV-ENABLED-LABEL: bb.1.exit +# LDV-ENABLED-NEXT: DBG_VALUE $rsp, 0, {{.*}}, !DIExpression(DW_OP_plus_uconst, 4) +# LDV-ENABLED-NEXT: $edi = MOV32rm + +--- | + target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128" + + declare i32 @use(i32) + + define i32 @foo(i32 %x) !dbg !6 { + entry: + %y = add i32 %x, %x, !dbg !12 + call void @llvm.dbg.value(metadata i32 %y, metadata !9, metadata !DIExpression()), !dbg !12 + br label %exit, !dbg !13 + + exit: ; preds = %entry + %z = call i32 @use(i32 %y), !dbg !14 + call void @llvm.dbg.value(metadata i32 %z, metadata !11, metadata !DIExpression()), !dbg !14 + ret i32 %z, !dbg !15 + } + + declare void @llvm.dbg.value(metadata, metadata, metadata) + + !llvm.dbg.cu = !{!0} + !llvm.debugify = !{!3, !4} + !llvm.module.flags = !{!5} + + !0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2) + !1 = !DIFile(filename: "/tmp/t.ll", directory: "/") + !2 = !{} + !3 = !{i32 4} + !4 = !{i32 2} + !5 = !{i32 2, !"Debug Info Version", i32 3} + !6 = distinct !DISubprogram(name: "foo", linkageName: "foo", scope: null, file: !1, line: 1, type: !7, scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !8) + !7 = !DISubroutineType(types: !2) + !8 = !{!9, !11} + !9 = !DILocalVariable(name: "1", scope: !6, file: !1, line: 1, type: !10) + !10 = !DIBasicType(name: "ty32", size: 32, encoding: DW_ATE_unsigned) + !11 = !DILocalVariable(name: "2", scope: !6, file: !1, line: 3, type: !10) + !12 = !DILocation(line: 1, column: 1, scope: !6) + !13 = !DILocation(line: 2, column: 1, scope: !6) + !14 = !DILocation(line: 3, column: 1, scope: !6) + !15 = !DILocation(line: 4, column: 1, scope: !6) + +... +--- +name: foo +liveins: + - { reg: '$edi', virtual-reg: '' } +stack: + - { id: 0, name: '', type: spill-slot, offset: -12, size: 4, alignment: 4, + stack-id: default, callee-saved-register: '', callee-saved-restored: true, + debug-info-variable: '', debug-info-expression: '', debug-info-location: '' } +body: | + bb.0.entry: + successors: %bb.1(0x80000000) + liveins: $edi + + frame-setup PUSH64r undef $rax, implicit-def $rsp, implicit $rsp + CFI_INSTRUCTION def_cfa_offset 16 + renamable $edi = ADD32rr renamable $edi, killed renamable $edi, implicit-def $eflags, debug-location !12 + DBG_VALUE renamable $edi, $noreg, !9, !DIExpression(), debug-location !12 + MOV32mr $rsp, 1, $noreg, 4, $noreg, killed $edi :: (store 4 into %stack.0) + DBG_VALUE $rsp, 0, !9, !DIExpression(DW_OP_plus_uconst, 4), debug-location !12 + + bb.1.exit: + $edi = MOV32rm $rsp, 1, $noreg, 4, $noreg :: (load 4 from %stack.0) + CALL64pcrel32 @use, csr_64, implicit $rsp, implicit $ssp, implicit killed $edi, implicit-def $eax, debug-location !14 + DBG_VALUE renamable $eax, $noreg, !11, !DIExpression(), debug-location !14 + $rcx = frame-destroy POP64r implicit-def $rsp, implicit $rsp, debug-location !15 + RETQ implicit killed $eax, debug-location !15 + +... -- 2.7.4