From 6e1009b65e985412267d5e263a99afbcdd5ae936 Mon Sep 17 00:00:00 2001
From: "Duncan P. N. Exon Smith" <dexonsmith@apple.com>
Date: Fri, 1 Aug 2014 22:27:19 +0000
Subject: UseListOrder: Fix blockaddress use-list order

`parseBitcodeFile()` uses the generic `getLazyBitcodeFile()` function as
a helper.  Since `parseBitcodeFile()` isn't actually lazy -- it calls
`MaterializeAllPermanently()` -- bypass the unnecessary call to
`materializeForwardReferencedFunctions()` by extracting out a common
helper function.  This removes the last of the use-list churn caused by
blockaddresses.

This highlights that we can't reproduce use-list order of globals and
constants when parsing lazily -- but that's necessarily out of scope.
When we're parsing lazily, we never have all the functions in memory, so
the use-lists of globals (and constants that reference globals) are
always incomplete.

This is part of PR5680.

llvm-svn: 214581
---
 llvm/lib/Bitcode/Reader/BitcodeReader.cpp | 26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)

(limited to 'llvm/lib/Bitcode/Reader/BitcodeReader.cpp')

diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
index 48fa9390..85dde39 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -3503,10 +3503,17 @@ const std::error_category &llvm::BitcodeErrorCategory() {
 // External interface
 //===----------------------------------------------------------------------===//
 
-/// getLazyBitcodeModule - lazy function-at-a-time loading from a file.
+/// \brief Get a lazy one-at-time loading module from bitcode.
 ///
-ErrorOr<Module *> llvm::getLazyBitcodeModule(MemoryBuffer *Buffer,
-                                             LLVMContext &Context) {
+/// This isn't always used in a lazy context.  In particular, it's also used by
+/// \a parseBitcodeFile().  If this is truly lazy, then we need to eagerly pull
+/// in forward-referenced functions from block address references.
+///
+/// \param[in] WillMaterializeAll Set to \c true if the caller promises to
+/// materialize everything -- in particular, if this isn't truly lazy.
+static ErrorOr<Module *> getLazyBitcodeModuleImpl(MemoryBuffer *Buffer,
+                                                  LLVMContext &Context,
+                                                  bool WillMaterializeAll) {
   Module *M = new Module(Buffer->getBufferIdentifier(), Context);
   BitcodeReader *R = new BitcodeReader(Buffer, Context);
   M->setMaterializer(R);
@@ -3520,12 +3527,18 @@ ErrorOr<Module *> llvm::getLazyBitcodeModule(MemoryBuffer *Buffer,
   if (std::error_code EC = R->ParseBitcodeInto(M))
     return cleanupOnError(EC);
 
-  if (std::error_code EC = R->materializeForwardReferencedFunctions())
-    return cleanupOnError(EC);
+  if (!WillMaterializeAll)
+    // Resolve forward references from blockaddresses.
+    if (std::error_code EC = R->materializeForwardReferencedFunctions())
+      return cleanupOnError(EC);
 
   return M;
 }
 
+ErrorOr<Module *> llvm::getLazyBitcodeModule(MemoryBuffer *Buffer,
+                                             LLVMContext &Context) {
+  return getLazyBitcodeModuleImpl(Buffer, Context, false);
+}
 
 Module *llvm::getStreamedBitcodeModule(const std::string &name,
                                        DataStreamer *streamer,
@@ -3545,7 +3558,8 @@ Module *llvm::getStreamedBitcodeModule(const std::string &name,
 
 ErrorOr<Module *> llvm::parseBitcodeFile(MemoryBuffer *Buffer,
                                          LLVMContext &Context) {
-  ErrorOr<Module *> ModuleOrErr = getLazyBitcodeModule(Buffer, Context);
+  ErrorOr<Module *> ModuleOrErr =
+      getLazyBitcodeModuleImpl(Buffer, Context, true);
   if (!ModuleOrErr)
     return ModuleOrErr;
   Module *M = ModuleOrErr.get();
-- 
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