[Assignment Tracking] Skip empty-metadata dbg.declares in AssignmentTrackingPass

[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.

Skip empty-metadata dbg.declares to avoid dereferencing the nullptr. This doesn't affect the final debug info in any way.

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.

[jryans]

Looks good, thanks! 🙂

[Orlando]

Thanks for the review!

llvm/lib/IR/DebugInfo.cpp

for (auto &I : BB) {
       DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(&I);
       if (!DDI)
         continue;
       // FIXME: trackAssignments doesn't let you specify any modifiers to the
       // variable (e.g. fragment) or location (e.g. offset), so we have to
       // leave dbg.declares with non-empty expressions in place.
       if (DDI->getExpression()->getNumElements() != 0)
         continue;
+      if (!DDI->getAddress())
+        continue;
       if (AllocaInst *Alloca =
               dyn_cast<AllocaInst>(DDI->getAddress()->stripPointerCasts())) {
         // FIXME: Skip VLAs for now (let these variables use dbg.declares).
         if (!Alloca->isStaticAlloca())
           continue;
         DbgDeclares[Alloca].insert(DDI);
         Vars[Alloca].insert(VarRecord(DDI));
       }

llvm/test/DebugInfo/Generic/assignment-tracking/declare-to-assign/nullptr-declare.ll

+; RUN: opt %s -passes=declare-to-assign -S | FileCheck %s
+
+;; Check AssignmentTrackingPass ignores a dbg.declare with an empty metadata
+;; location operand.
+
+; CHECK:      call void @llvm.dbg.declare
+; CHECK-NOT:  call void @llvm.dbg.assign
+
+define dso_local void @_Z3funv() #0 !dbg !10 {
+entry:
+  call void @llvm.dbg.declare(metadata !13, metadata !14, metadata !DIExpression()), !dbg !16
+  ret void
+}
+
+declare void @llvm.dbg.declare(metadata, metadata, metadata) #1
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3}
+!llvm.ident = !{!9}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 17.0.0", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "test.cpp", directory: "/")
+!2 = !{i32 7, !"Dwarf Version", i32 5}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!9 = !{!"clang version 17.0.0"}
+!10 = distinct !DISubprogram(name: "fun", linkageName: "_Z3funv", scope: !1, file: !1, line: 1, type: !11, scopeLine: 1, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !13)
+!11 = !DISubroutineType(types: !12)
+!12 = !{null}
+!13 = !{}
+!14 = !DILocalVariable(name: "x", scope: !10, file: !1, line: 1, type: !15)
+!15 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!16 = !DILocation(line: 1, column: 18, scope: !10)