[PATCH] D109869: [LTO] An option to disable automatic bitcode upgrade

[Hongtao Yu via Phabricator via llvm-commits]

hoy created this revision.
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Bitcode upgrade automatically takes in place when the current compiler version doesn't match the one building the input modules. The upgrade is very expansive for large applications and unnecessary when users are sure the two compilers do not have a version issue, even if their versions mismatch literally. An optional to disable the automatic bitcode upgrade will be handy in such case.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D109869

Files:
  llvm/lib/Object/IRSymtab.cpp


Index: llvm/lib/Object/IRSymtab.cpp
===================================================================
--- llvm/lib/Object/IRSymtab.cpp
+++ llvm/lib/Object/IRSymtab.cpp
@@ -14,6 +14,7 @@
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Triple.h"
+#include "llvm/Bitcode/BitcodeReader.h"
 #include "llvm/Config/llvm-config.h"
 #include "llvm/IR/Comdat.h"
 #include "llvm/IR/DataLayout.h"
@@ -22,13 +23,13 @@
 #include "llvm/IR/Mangler.h"
 #include "llvm/IR/Metadata.h"
 #include "llvm/IR/Module.h"
-#include "llvm/Bitcode/BitcodeReader.h"
 #include "llvm/MC/StringTableBuilder.h"
 #include "llvm/Object/IRObjectFile.h"
 #include "llvm/Object/ModuleSymbolTable.h"
 #include "llvm/Object/SymbolicFile.h"
 #include "llvm/Support/Allocator.h"
 #include "llvm/Support/Casting.h"
+#include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/StringSaver.h"
 #include "llvm/Support/VCSRevision.h"
@@ -41,6 +42,11 @@
 using namespace llvm;
 using namespace irsymtab;
 
+cl::opt<bool>
+    DisableBitcodeUpgrade("disable-bitcode-upgrade", cl::init(false),
+                          cl::Hidden,
+                          cl::desc("Disable automatic bitcode upgrade"));
+
 static const char *LibcallRoutineNames[] = {
 #define HANDLE_LIBCALL(code, name) name,
 #include "llvm/IR/RuntimeLibcalls.def"
@@ -393,20 +399,22 @@
     return make_error<StringError>("Bitcode file does not contain any modules",
                                    inconvertibleErrorCode());
 
-  if (BFC.StrtabForSymtab.empty() ||
-      BFC.Symtab.size() < sizeof(storage::Header))
-    return upgrade(BFC.Mods);
-
-  // We cannot use the regular reader to read the version and producer, because
-  // it will expect the header to be in the current format. The only thing we
-  // can rely on is that the version and producer will be present as the first
-  // struct elements.
-  auto *Hdr = reinterpret_cast<const storage::Header *>(BFC.Symtab.data());
-  unsigned Version = Hdr->Version;
-  StringRef Producer = Hdr->Producer.get(BFC.StrtabForSymtab);
-  if (Version != storage::Header::kCurrentVersion ||
-      Producer != kExpectedProducerName)
-    return upgrade(BFC.Mods);
+  if (!DisableBitcodeUpgrade) {
+    if (BFC.StrtabForSymtab.empty() ||
+        BFC.Symtab.size() < sizeof(storage::Header))
+      return upgrade(BFC.Mods);
+
+    // We cannot use the regular reader to read the version and producer,
+    // because it will expect the header to be in the current format. The only
+    // thing we can rely on is that the version and producer will be present as
+    // the first struct elements.
+    auto *Hdr = reinterpret_cast<const storage::Header *>(BFC.Symtab.data());
+    unsigned Version = Hdr->Version;
+    StringRef Producer = Hdr->Producer.get(BFC.StrtabForSymtab);
+    if (Version != storage::Header::kCurrentVersion ||
+        Producer != kExpectedProducerName)
+      return upgrade(BFC.Mods);
+  }
 
   FileContents FC;
   FC.TheReader = {{BFC.Symtab.data(), BFC.Symtab.size()},
@@ -416,8 +424,9 @@
   // the number of modules in the bitcode file. If they differ, it may mean that
   // the bitcode file was created by binary concatenation, so we need to create
   // a new symbol table from scratch.
-  if (FC.TheReader.getNumModules() != BFC.Mods.size())
-    return upgrade(std::move(BFC.Mods));
+  if (!DisableBitcodeUpgrade)
+    if (FC.TheReader.getNumModules() != BFC.Mods.size())
+      return upgrade(std::move(BFC.Mods));
 
   return std::move(FC);
 }


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