[RemoveDIs] Add flag to preserve the debug info format of input IR (#87379)

This patch adds a new flag: `--preserve-input-debuginfo-format`

This flag instructs the tool to not convert the debug info format
(intrinsics/records) of input IR, but to instead determine the format of
the input IR and overwrite the other format-determining flags so that we
process and output the file in the same format that we received it in.
This flag is turned off by llvm-link, llvm-lto, and llvm-lto2, and
should be turned off by any other tool that expects to parse multiple IR
modules and have their debug info formats match.

The motivation for this flag is to allow tools to not convert the debug
info format - verify-uselistorder and llvm-reduce, and any downstream
tools that seek to test or mutate IR as-is, without applying extraneous
modifications to the input. This is a necessary step to using debug
records by default in all (other) LLVM tools.

1 files changed, 59 insertions, 13 deletions

diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
index aa6c9c9..5ea6cc2 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -108,6 +108,9 @@ cl::opt<cl::boolOrDefault> LoadBitcodeIntoNewDbgInfoFormat(
     "load-bitcode-into-experimental-debuginfo-iterators", cl::Hidden,
     cl::desc("Load bitcode directly into the new debug info format (regardless "
              "of input format)"));
+extern cl::opt<cl::boolOrDefault> PreserveInputDbgFormat;
+extern bool WriteNewDbgInfoFormatToBitcode;
+extern cl::opt<bool> WriteNewDbgInfoFormat;
 
 namespace {
 
@@ -682,6 +685,11 @@ class BitcodeReader : public BitcodeReaderBase, public GVMaterializer {
   /// (e.g.) blockaddress forward references.
   bool WillMaterializeAllForwardRefs = false;
 
+  /// Tracks whether we have seen debug intrinsics or records in this bitcode;
+  /// seeing both in a single module is currently a fatal error.
+  bool SeenDebugIntrinsic = false;
+  bool SeenDebugRecord = false;
+
   bool StripDebugInfo = false;
   TBAAVerifier TBAAVerifyHelper;
 
@@ -3774,7 +3782,11 @@ Error BitcodeReader::globalCleanup() {
   for (Function &F : *TheModule) {
     MDLoader->upgradeDebugIntrinsics(F);
     Function *NewFn;
-    if (UpgradeIntrinsicFunction(&F, NewFn))
+    // If PreserveInputDbgFormat=true, then we don't know whether we want
+    // intrinsics or records, and we won't perform any conversions in either
+    // case, so don't upgrade intrinsics to records.
+    if (UpgradeIntrinsicFunction(
+            &F, NewFn, PreserveInputDbgFormat != cl::boolOrDefault::BOU_TRUE))
       UpgradedIntrinsics[&F] = NewFn;
     // Look for functions that rely on old function attribute behavior.
     UpgradeFunctionAttributes(F);
@@ -4301,10 +4313,13 @@ Error BitcodeReader::parseModule(uint64_t ResumeBit,
                                  bool ShouldLazyLoadMetadata,
                                  ParserCallbacks Callbacks) {
   // Load directly into RemoveDIs format if LoadBitcodeIntoNewDbgInfoFormat
-  // has been set to true (default action: load into the old debug format).
-  TheModule->IsNewDbgInfoFormat =
-      UseNewDbgInfoFormat &&
-      LoadBitcodeIntoNewDbgInfoFormat == cl::boolOrDefault::BOU_TRUE;
+  // has been set to true and we aren't attempting to preserve the existing
+  // format in the bitcode (default action: load into the old debug format).
+  if (PreserveInputDbgFormat != cl::boolOrDefault::BOU_TRUE) {
+    TheModule->IsNewDbgInfoFormat =
+        UseNewDbgInfoFormat &&
+        LoadBitcodeIntoNewDbgInfoFormat == cl::boolOrDefault::BOU_TRUE;
+  }
 
   this->ValueTypeCallback = std::move(Callbacks.ValueType);
   if (ResumeBit) {
@@ -6453,6 +6468,7 @@ Error BitcodeReader::parseFunctionBody(Function *F) {
     case bitc::FUNC_CODE_DEBUG_RECORD_ASSIGN: {
       // DbgVariableRecords are placed after the Instructions that they are
       // attached to.
+      SeenDebugRecord = true;
       Instruction *Inst = getLastInstruction();
       if (!Inst)
         return error("Invalid dbg record: missing instruction");
@@ -6613,6 +6629,8 @@ Error BitcodeReader::parseFunctionBody(Function *F) {
         TCK = CallInst::TCK_NoTail;
       cast<CallInst>(I)->setTailCallKind(TCK);
       cast<CallInst>(I)->setAttributes(PAL);
+      if (isa<DbgInfoIntrinsic>(I))
+        SeenDebugIntrinsic = true;
       if (Error Err = propagateAttributeTypes(cast<CallBase>(I), ArgTyIDs)) {
         I->deleteValue();
         return Err;
@@ -6801,20 +6819,48 @@ Error BitcodeReader::materialize(GlobalValue *GV) {
   if (Error JumpFailed = Stream.JumpToBit(DFII->second))
     return JumpFailed;
 
-  // Set the debug info mode to "new", possibly creating a mismatch between
-  // module and function debug modes. This is okay because we'll convert
-  // everything back to the old mode after parsing if needed.
-  // FIXME: Remove this once all tools support RemoveDIs.
+  // Regardless of the debug info format we want to end up in, we need
+  // IsNewDbgInfoFormat=true to construct any debug records seen in the bitcode.
   F->IsNewDbgInfoFormat = true;
 
   if (Error Err = parseFunctionBody(F))
     return Err;
   F->setIsMaterializable(false);
 
-  // Convert new debug info records into intrinsics.
-  // FIXME: Remove this once all tools support RemoveDIs.
-  if (!F->getParent()->IsNewDbgInfoFormat)
-    F->convertFromNewDbgValues();
+  // All parsed Functions should load into the debug info format dictated by the
+  // Module, unless we're attempting to preserve the input debug info format.
+  if (SeenDebugIntrinsic && SeenDebugRecord)
+    return error("Mixed debug intrinsics and debug records in bitcode module!");
+  if (PreserveInputDbgFormat == cl::boolOrDefault::BOU_TRUE) {
+    bool SeenAnyDebugInfo = SeenDebugIntrinsic || SeenDebugRecord;
+    bool NewDbgInfoFormatDesired =
+        SeenAnyDebugInfo ? SeenDebugRecord : F->getParent()->IsNewDbgInfoFormat;
+    if (SeenAnyDebugInfo) {
+      UseNewDbgInfoFormat = SeenDebugRecord;
+      WriteNewDbgInfoFormatToBitcode = SeenDebugRecord;
+      WriteNewDbgInfoFormat = SeenDebugRecord;
+    }
+    // If the module's debug info format doesn't match the observed input
+    // format, then set its format now; we don't need to call the conversion
+    // function because there must be no existing intrinsics to convert.
+    // Otherwise, just set the format on this function now.
+    if (NewDbgInfoFormatDesired != F->getParent()->IsNewDbgInfoFormat)
+      F->getParent()->setNewDbgInfoFormatFlag(NewDbgInfoFormatDesired);
+    else
+      F->setNewDbgInfoFormatFlag(NewDbgInfoFormatDesired);
+  } else {
+    // If we aren't preserving formats, we use the Module flag to get our
+    // desired format instead of reading flags, in case we are lazy-loading and
+    // the format of the module has been changed since it was set by the flags.
+    // We only need to convert debug info here if we have debug records but
+    // desire the intrinsic format; everything else is a no-op or handled by the
+    // autoupgrader.
+    bool ModuleIsNewDbgInfoFormat = F->getParent()->IsNewDbgInfoFormat;
+    if (ModuleIsNewDbgInfoFormat || !SeenDebugRecord)
+      F->setNewDbgInfoFormatFlag(ModuleIsNewDbgInfoFormat);
+    else
+      F->setIsNewDbgInfoFormat(ModuleIsNewDbgInfoFormat);
+  }
 
   if (StripDebugInfo)
     stripDebugInfo(*F);