Support !heapallocsite attachments in StripDebugInfo().

[aprantl]

Summary

They point into the DIType type system, so they need to be stripped as well.

rdar://75341300

[dexonsmith]

LGTM.

[vsk]

llvm/lib/IR/DebugInfo.cpp

350

Is it possible to reach this when the instruction has no heapallocsite metadata?

If so, we might want a narrower change, like:

if (auto *MD = I.getMetadata("heapallocsite"))
  I.setMetadata("heapallocsite", nullptr);

Or we might want to guarantee that we drop non-debug metadata, like:

I.dropUnknownNonDebugMetadata();

Ditto for D98667.

[dexonsmith]

llvm/lib/IR/DebugInfo.cpp

350

Is it possible to reach this when the instruction has no heapallocsite metadata?

It is possible, but the code as written is correct. nullptr here effectively means "delete if exists".

We could (maybe should?) drop the if entirely and always do:

I.setMetadata("healallocsite", nullptr);

since Instruction::setMetadata has an early return for exactly the checked condition.

Or we might want to guarantee that we drop non-debug metadata, like:

Dropping non-debug metadata when stripping debug info sounds dangerous to me, since debug info is not supposed to have an impact on optimizations. (I was worried at first when I saw this patch because heapallocsite sounds like an optimization hint -- in which case I was going to suggest replacing the metadata with a remapped / equivalent version -- but git grep told me it's only used for debug info. Probably it should be renamed dbg.heapallocsite or something to make it clear that it shouldn't be used for anything else...)

[vsk]

llvm/lib/IR/DebugInfo.cpp

350

Dropping the check for I.hasMetadataOtherThanDebugLoc() and renaming "heapallocsite" to "dbg.heapallocsite" (or similar) both sound good to me (cc'ing @akhuang).

llvm/lib/IR/DebugInfo.cpp

for (auto II = BB.begin(), End = BB.end(); II != End;) {
       }
       if (auto *LoopID = I.getMetadata(LLVMContext::MD_loop)) {
         auto *NewLoopID = LoopIDsMap.lookup(LoopID);
         if (!NewLoopID)
           NewLoopID = LoopIDsMap[LoopID] = stripDebugLocFromLoopID(LoopID);
         if (NewLoopID != LoopID)
           I.setMetadata(LLVMContext::MD_loop, NewLoopID);
       }
+      // Strip heapallocsite attachments, they point into the DIType system.
+      if (I.hasMetadataOtherThanDebugLoc())
+        I.setMetadata("heapallocsite", nullptr);
     }
   }
   return Changed;
 }
 
 bool llvm::StripDebugInfo(Module &M) {
   bool Changed = false;
 

llvm/test/Transforms/Util/strip-nonlinetable-debuginfo-heapallocsite.ll

 ; RUN: opt -S -strip-nonlinetable-debuginfo %s -o - |  FileCheck %s
+; RUN: opt -S -strip-debug %s -o - |  FileCheck %s
 ; int *get() { return new int[256]; }
 ; ModuleID = '/tmp/heapallocsite.cpp'
 source_filename = "/tmp/heapallocsite.cpp"
 target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-apple-macosx11.0.0"
 
 ; Function Attrs: noinline optnone ssp uwtable mustprogress
 define dso_local i32* @_Z3getv() #0 !dbg !8 {

 attributes #0 = { noinline optnone ssp uwtable mustprogress }
 attributes #1 = { nobuiltin allocsize(0) "frame-pointer"="all" }
 attributes #2 = { builtin allocsize(0) }
 
 !llvm.dbg.cu = !{!0}
 !llvm.module.flags = !{!3, !4, !5, !6}
 !llvm.ident = !{!7}
 
-; CHECK-LABEL: !0 =
+; CHECK-LABEL: !llvm.ident
 ; CHECK-NOT: !DIBasicType(name: "int"
 !0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 13.0.0 ([e-mail]:llvm/llvm-project 6d4ce49dae17715de502acbd50ab4c9b3c18215b)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, nameTableKind: None, sysroot: "/")
 !1 = !DIFile(filename: "/tmp/heapallocsite.cpp", directory: "/Volumes/Data/llvm-project")
 !2 = !{}
 !3 = !{i32 7, !"Dwarf Version", i32 4}
 !4 = !{i32 2, !"Debug Info Version", i32 3}
 !5 = !{i32 1, !"wchar_size", i32 4}
 !6 = !{i32 7, !"PIC Level", i32 2}