[Assignment Tracking][19/*] Account for assignment tracking in ADCE

[Orlando]

Summary

Don't delete linked dbg.assign intrinsics. An alternative could just be to do nothing (delete all debug intrinsics that satisfy the normal conditions).

[jmorse]

LGTM

llvm/lib/Transforms/Scalar/ADCE.cpp

 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/Analysis/DomTreeUpdater.h"
 #include "llvm/Analysis/GlobalsModRef.h"
 #include "llvm/Analysis/IteratedDominanceFrontier.h"
 #include "llvm/Analysis/PostDominators.h"
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/CFG.h"
+#include "llvm/IR/DebugInfo.h"
 #include "llvm/IR/DebugInfoMetadata.h"
 #include "llvm/IR/DebugLoc.h"
 #include "llvm/IR/Dominators.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/IR/InstIterator.h"
 #include "llvm/IR/Instruction.h"
 #include "llvm/IR/Instructions.h"
bool AggressiveDeadCodeElimination::removeDeadInstructions() {
   // value of the function, and may therefore be deleted safely.
   // NOTE: We reuse the Worklist vector here for memory efficiency.
   for (Instruction &I : llvm::reverse(instructions(F))) {
     // Check if the instruction is alive.
     if (isLive(&I))
       continue;
 
     if (auto *DII = dyn_cast<DbgInfoIntrinsic>(&I)) {
+      // Avoid removing a dbg.assign that is linked to instructions because it
+      // holds information about an existing store.
+      if (auto *DAI = dyn_cast<DbgAssignIntrinsic>(DII))
+        if (!at::getAssignmentInsts(DAI).empty())
+          continue;
       // Check if the scope of this variable location is alive.
       if (AliveScopes.count(DII->getDebugLoc()->getScope()))
         continue;
 
       // Fallthrough and drop the intrinsic.
     }
 
     // Prepare to delete.

llvm/test/DebugInfo/Generic/assignment-tracking/adce/no-delete.ll

+; RUN: opt %s -passes=adce -experimental-assignment-tracking -S -o - \
+; RUN: | FileCheck %s
+
+;; $ cat test.c
+;; void fun(int local) {}
+;;
+;; $ clang test.c -g -O1 -Xclang -disable-llvm-passes | opt -S -passes=declare-to-assign
+
+;; Check that the dbg.assign intrinsics that are considered "out of scope" (dbg
+;; attachments have been deleted) but still linked to an instruction are not
+;; deleted by ADCE.
+
+; CHECK: llvm.dbg.assign
+; CHECK: llvm.dbg.assign
+
+define dso_local void @fun(i32 noundef %local) #0 !dbg !7 {
+entry:
+  %local.addr = alloca i32, align 4, !DIAssignID !13
+  call void @llvm.dbg.assign(metadata i1 undef, metadata !12, metadata !DIExpression(), metadata !13, metadata ptr %local.addr, metadata !DIExpression()), !dbg !14
+  store i32 %local, ptr %local.addr, align 4, !DIAssignID !19
+  call void @llvm.dbg.assign(metadata i32 %local, metadata !12, metadata !DIExpression(), metadata !19, metadata ptr %local.addr, metadata !DIExpression()), !dbg !14
+  ret void
+}
+
+declare void @llvm.dbg.declare(metadata, metadata, metadata)
+declare void @llvm.dbg.assign(metadata, metadata, metadata, metadata, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 14.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "test.c", directory: "/")
+!2 = !{i32 7, !"Dwarf Version", i32 5}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !{i32 1, !"wchar_size", i32 4}
+!5 = !{i32 7, !"uwtable", i32 1}
+!6 = !{!"clang version 14.0.0"}
+!7 = distinct !DISubprogram(name: "fun", scope: !1, file: !1, line: 1, type: !8, scopeLine: 1, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !11)
+!8 = !DISubroutineType(types: !9)
+!9 = !{null, !10}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !{!12}
+!12 = !DILocalVariable(name: "local", arg: 1, scope: !7, file: !1, line: 1, type: !10)
+!13 = distinct !DIAssignID()
+!14 = !DILocation(line: 0, scope: !7)
+!19 = distinct !DIAssignID()
+!20 = !DILocation(line: 1, column: 22, scope: !7)