[PATCH] D108134: [DebugInfo][InstrRef] Remove a faulty assertion
Jeremy Morse via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Mon Aug 16 08:09:15 PDT 2021
jmorse created this revision.
jmorse added reviewers: StephenTozer, Orlando, TWeaver.
Herald added subscribers: pengfei, hiraditya.
jmorse requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.
This patch removes an assertion, and adds a regression test showing why the assertion is broken.
For context, `LocIdx` is a key/index number for machine locations, so that we can describe locations as a single integer and ignore whether they're on the stack, in registers or otherwise. Back when InstrRefBasedLDV was added, I happened to bake in a "special" zero number for various reasons, which Vedant identified as undesirable in this review comment: https://reviews.llvm.org/D83047#inline-765495 . I subsequently removed that special zero number, but it looks like I didn't delete this assertion at the time, which assumes that a zero LocIdx is invalid.
The attached test shows that this assertion is reachable on valid code -- on x86 $rsp always gets the LocIdx number zero, and if you transfer a variable value into it, InstrRefBasedLDV crashes on that assertion. The code might be a bit wild to be storing variables to $rsp like that, however we shouldn't crash on it.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D108134
Files:
llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp
llvm/test/DebugInfo/MIR/InstrRef/restore-to-rsp-crash.mir
Index: llvm/test/DebugInfo/MIR/InstrRef/restore-to-rsp-crash.mir
===================================================================
--- /dev/null
+++ llvm/test/DebugInfo/MIR/InstrRef/restore-to-rsp-crash.mir
@@ -0,0 +1,67 @@
+# RUN: llc %s -o - -mtriple=x86_64-unknown-unknown \
+# RUN: -experimental-debug-variable-locations -run-pass=livedebugvalues\
+# RUN: | FileCheck %s
+#
+# Regression test for a rare crash with InstrRefBasedLDV. It would be quite
+# wild for a transfer (copy/spill/restore) instruction to write to $rsp, but if
+# it did, we hit a stale assertion that made assumptions about the numbering
+# order of location numbers. Test that this input (transferring to $rsp via
+# a stack restore) doesn't crash.
+#
+--- |
+ 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 @foo(i64 %bar, i64 %baz) !dbg !7 {
+ entry:
+ ret i32 0
+ }
+
+ declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+ !llvm.dbg.cu = !{!0}
+ !llvm.module.flags = !{!3, !4, !5}
+ !llvm.ident = !{!6}
+
+ !0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, splitDebugInlining: false, nameTableKind: None)
+ !1 = !DIFile(filename: "test.c", directory: "/tmp/out.c")
+ !2 = !{}
+ !3 = !{i32 7, !"Dwarf Version", i32 4}
+ !4 = !{i32 2, !"Debug Info Version", i32 3}
+ !5 = !{i32 1, !"wchar_size", i32 4}
+ !6 = !{!""}
+ !7 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 3, type: !8, scopeLine: 3, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !2)
+ !8 = !DISubroutineType(types: !9)
+ !9 = !{!10, !11, !11}
+ !10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+ !11 = !DIBasicType(name: "long int", size: 64, encoding: DW_ATE_signed)
+ !12 = !DILocalVariable(name: "bar", arg: 1, scope: !7, file: !1, line: 3, type: !11)
+ !13 = !DILocation(line: 0, scope: !7)
+ !14 = !DILocalVariable(name: "baz", arg: 2, scope: !7, file: !1, line: 3, type: !11)
+
+...
+---
+name: foo
+alignment: 16
+tracksRegLiveness: true
+frameInfo:
+ stackSize: 24
+ offsetAdjustment: -24
+ maxAlignment: 1
+ adjustsStack: true
+ hasCalls: true
+ maxCallFrameSize: 0
+ cvBytesOfCalleeSavedRegisters: 16
+stack:
+ - { id: 0, type: spill-slot, offset: -64, size: 8, alignment: 8 }
+machineFunctionInfo: {}
+body: |
+ bb.0.entry:
+ liveins: $rax, $rbx
+
+ DBG_VALUE $rax, $noreg, !12, !DIExpression(), debug-location !13
+ MOV64mr $rsp, 1, $noreg, -8, $noreg, renamable $rax :: (store 8 into %stack.0)
+ $rsp = MOV64rm $rsp, 1, $noreg, 0, $noreg, debug-location !13 :: (load 8 from %stack.0)
+ RETQ implicit $rbx, debug-location !13
+
+...
Index: llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp
===================================================================
--- llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp
+++ llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp
@@ -1381,7 +1381,6 @@
assert(ActiveVLocIt != ActiveVLocs.end());
ActiveVLocIt->second.Loc = Dst;
- assert(Dst != 0);
MachineInstr *MI =
MTracker->emitLoc(Dst, Var, ActiveVLocIt->second.Properties);
PendingDbgValues.push_back(MI);
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