[Assignment Tracking][SelectionDAG] Fix dereferencing nullptr location from dbg.declare

[Orlando]

Summary

Debug intrinsics sometimes end up with empty metadata location operands. The debug intrinsic interfaces return nullptr when retrieving location operand in this case.

When assignment tracking is not enabled a dbg.declare with a nullptr location operand is skipped. Do the same when assignment tracking is enabled (a nullptr address component of a dbg.assign is already handled correctly.

N.B. my "empty metadata is the same as poison" patch stack (D140902) hasn't landed yet as I'm focussing on assignment tracking for now.

[jmorse]

LGTM

llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp

return !I->mayWriteToMemory() && // Side-effecting instructions aren't folded.
          !isa<DbgInfoIntrinsic>(I) && // Debug instructions aren't folded.
          !I->isEHPad() &&             // EH pad instructions aren't folded.
          !FuncInfo.isExportedInst(I); // Exported instrs must be computed.
 }
 
 static void processDbgDeclare(FunctionLoweringInfo &FuncInfo,
                               const Value *Address, DIExpression *Expr,
                               DILocalVariable *Var, DebugLoc DbgLoc) {
+  if (!Address) {
+    LLVM_DEBUG(dbgs() << "processDbgDeclares skipping " << *Var
+                      << " (bad address)\n");
+    return;
+  }
   MachineFunction *MF = FuncInfo.MF;
   const DataLayout &DL = MF->getDataLayout();
 
   assert(Var && "Missing variable");
   assert(DbgLoc && "Missing location");
 
   // Look through casts and constant offset GEPs. These mostly come from
   // inalloca.

 }
 
 /// Collect llvm.dbg.declare information. This is done after argument lowering
 /// in case the declarations refer to arguments.
 static void processDbgDeclares(FunctionLoweringInfo &FuncInfo) {
   for (const BasicBlock &BB : *FuncInfo.Fn) {
     for (const Instruction &I : BB) {
       if (const DbgDeclareInst *DI = dyn_cast<DbgDeclareInst>(&I)) {
-        Value *Address = DI->getAddress();
-        if (!Address) {
-          LLVM_DEBUG(dbgs() << "processDbgDeclares skipping " << *DI
-                            << " (bad address)\n");
-          continue;
-        }
-        processDbgDeclare(FuncInfo, Address, DI->getExpression(),
+        processDbgDeclare(FuncInfo, DI->getAddress(), DI->getExpression(),
                           DI->getVariable(), DI->getDebugLoc());
       }
     }
   }
 }
 
 /// Collect single location variable information generated with assignment
 /// tracking. This is done after argument lowering in case the declarations

llvm/test/DebugInfo/assignment-tracking/X86/single-memory-location.ll

 ; RUN: llc -stop-after=finalize-isel %s -o - \
 ; RUN: | FileCheck %s
 
 ;; Check that a dbg.assign for a fully stack-homed variable causes the variable
-;; location to appear in the Machine Function side table.
+;; location to appear in the Machine Function side table (variable 'local').
+;;
+;; The variable 'local2' is tracked using a dbg.declare. Check the variable is
+;; dropped and doesn't cause a crash when the address is an empty metadata
+;; tuple and assignment tracking is enabled for the function.
 ;;
 ;; $ cat test.cpp
 ;; void maybe_writes(int*);
 ;; void ext(int, int, int, int, int, int, int, int, int, int);
 ;; int example() {
 ;;    int local;
 ;;    maybe_writes(&local);
 ;;    ext(0, 1, 2, 3, 4, 5, 6, 7, 8, 9);
 ;;    return local;
 ;; }
 ;; $ clang++ -O2 -g -emit-llvm -S -c -Xclang -fexperimental-assignment-tracking
 
 ; CHECK: ![[VAR:[0-9]+]] = !DILocalVariable(name: "local",
 ; CHECK: stack:
-; CHECK-NEXT: - { id: 0, name: local, type: default, offset: 0, size: 4, alignment: 4, 
-; CHECK-NEXT:     stack-id: default, callee-saved-register: '', callee-saved-restored: true, 
-; CHECK-NEXT:     debug-info-variable: '![[VAR]]', debug-info-expression: '!DIExpression()', 
+; CHECK-NEXT: - { id: 0, name: local, type: default, offset: 0, size: 4, alignment: 4,
+; CHECK-NEXT:     stack-id: default, callee-saved-register: '', callee-saved-restored: true,
+; CHECK-NEXT:     debug-info-variable: '![[VAR]]', debug-info-expression: '!DIExpression()',
 ; CHECK-NEXT:     debug-info-location: '!{{.+}}' }
+; CHECK-NEXT: - { id: 1, name: local2, type: default, offset: 0, size: 4, alignment: 4,
+; CHECK-NEXT:     stack-id: default, callee-saved-register: '', callee-saved-restored: true,
+; CHECK-NEXT:     debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
 
 source_filename = "test.cpp"
 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 @_Z7examplev() local_unnamed_addr !dbg !7 {
 entry:
   %local = alloca i32, align 4, !DIAssignID !13
   call void @llvm.dbg.assign(metadata i1 undef, metadata !12, metadata !DIExpression(), metadata !13, metadata ptr %local, metadata !DIExpression()), !dbg !14
+  %local2 = alloca i32, align 4
+  call void @llvm.dbg.declare(metadata !2, metadata !32, metadata !DIExpression()), !dbg !14
   %0 = bitcast ptr %local to ptr, !dbg !15
   call void @llvm.lifetime.start.p0i8(i64 4, ptr nonnull %0), !dbg !15
   call void @_Z12maybe_writesPi(ptr nonnull %local), !dbg !16
   call void @_Z3extiiiiiiiiii(i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7, i32 8, i32 9), !dbg !17
   %1 = load i32, ptr %local, align 4, !dbg !18
   call void @llvm.lifetime.end.p0i8(i64 4, ptr nonnull %0), !dbg !23
   ret i32 %1, !dbg !24
 }
 
 declare !dbg !25 dso_local void @_Z12maybe_writesPi(ptr) local_unnamed_addr
 declare !dbg !29 dso_local void @_Z3extiiiiiiiiii(i32, i32, i32, i32, i32, i32, i32, i32, i32, i32) local_unnamed_addr
 declare void @llvm.lifetime.start.p0i8(i64 immarg, ptr nocapture)
 declare void @llvm.lifetime.end.p0i8(i64 immarg, ptr nocapture)
 declare void @llvm.dbg.assign(metadata, metadata, metadata, metadata, metadata, metadata)
+declare void @llvm.dbg.declare(metadata, metadata, metadata)
 
 !llvm.dbg.cu = !{!0}
 !llvm.module.flags = !{!3, !4, !5, !1000}
 !llvm.ident = !{!6}
 
 !0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 12.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, splitDebugInlining: false, nameTableKind: None)
 !1 = !DIFile(filename: "test.cpp", directory: "/")
 !2 = !{}

 !24 = !DILocation(line: 7, column: 4, scope: !7)
 !25 = !DISubprogram(name: "maybe_writes", linkageName: "_Z12maybe_writesPi", scope: !1, file: !1, line: 1, type: !26, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized, retainedNodes: !2)
 !26 = !DISubroutineType(types: !27)
 !27 = !{null, !28}
 !28 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !10, size: 64)
 !29 = !DISubprogram(name: "ext", linkageName: "_Z3extiiiiiiiiii", scope: !1, file: !1, line: 2, type: !30, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized, retainedNodes: !2)
 !30 = !DISubroutineType(types: !31)
 !31 = !{null, !10, !10, !10, !10, !10, !10, !10, !10, !10, !10}
+!32 = !DILocalVariable(name: "local2", scope: !7, file: !1, line: 4, type: !10)
 !1000 = !{i32 7, !"debug-info-assignment-tracking", i1 true}