[RemoveDIs][DebugInfo] Check for null marker when printing DPValues (llvm#82238)

The function to print DPValues currently tries to incorporate the
function it is part of, which is found through its marker; this means
when we try to print a DPValue with no marker, we dereference a nullptr.
We can print instructions without parents, and so the same should be
true for DPValues; this patch changes DPValue::print to check for a null
marker and avoid dereferencing it.

Fixes issue: llvm#82230

Author: SLTozer

llvm/lib/IR/AsmWriter.cpp

@@ -293,7 +293,7 @@ static const Module *getModuleFromDPI(const DPMarker *Marker) {
 }
 
 static const Module *getModuleFromDPI(const DPValue *DPV) {
-  return getModuleFromDPI(DPV->getMarker());
+  return DPV->getMarker() ? getModuleFromDPI(DPV->getMarker()) : nullptr;
 }
 
 static void PrintCallingConv(unsigned cc, raw_ostream &Out) {
@@ -4886,8 +4886,9 @@ void DPValue::print(raw_ostream &ROS, ModuleSlotTracker &MST,
     if (F)
       MST.incorporateFunction(*F);
   };
-  incorporateFunction(Marker->getParent() ? Marker->getParent()->getParent()
-                                          : nullptr);
+  incorporateFunction(Marker && Marker->getParent()
+                          ? Marker->getParent()->getParent()
+                          : nullptr);
   AssemblyWriter W(OS, SlotTable, getModuleFromDPI(this), nullptr, IsForDebug);
   W.printDPValue(*this);
 }

llvm/test/DebugInfo/dpvalue-print-nocrash.ll

@@ -0,0 +1,36 @@
+;; Tests that we can debug-print DPValues that have no markers attached.
+; RUN: opt -passes="instcombine" -debug %s -o /dev/null 2>&1 | FileCheck %s
+; REQUIRES: asserts
+
+; CHECK: CLONE:   DPValue value {
+; CHECK-SAME: marker @0x0
+
+define ptr @func_10(i32 %p_11) {
+entry:
+  %conv108 = zext i32 %p_11 to i64
+  tail call void @llvm.dbg.value(metadata i64 %conv108, metadata !4, metadata !DIExpression()), !dbg !12
+  br label %func_29.exit
+
+func_29.exit:                                     ; preds = %entry
+  store i64 %conv108, ptr null, align 1
+  ret ptr null
+}
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C11, file: !1, producer: "clang", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, retainedTypes: !2, globals: !2, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "csmith5961503756960.c", directory: "/llvm")
+!2 = !{}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !DILocalVariable(name: "p_31", arg: 2, scope: !5, file: !1, line: 148, type: !7)
+!5 = distinct !DISubprogram(name: "func_29", scope: !1, file: !1, line: 148, type: !6, scopeLine: 149, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagLocalToUnit | DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2)
+!6 = !DISubroutineType(types: !2)
+!7 = !DIDerivedType(tag: DW_TAG_typedef, name: "uint64_t", file: !8, line: 60, baseType: !9)
+!8 = !DIFile(filename: "/foo/_stdint.h", directory: "")
+!9 = !DIDerivedType(tag: DW_TAG_typedef, name: "__uint64_t", file: !10, line: 108, baseType: !11)
+!10 = !DIFile(filename: "/foo/_default_types.h", directory: "")
+!11 = !DIBasicType(name: "unsigned long long", size: 64, encoding: DW_ATE_unsigned)
+!12 = !DILocation(line: 0, scope: !5)