From 1d8c9d95bfc81d438dcfdc8e37fbd720c00e2eca Mon Sep 17 00:00:00 2001
From: "Duncan P. N. Exon Smith" <dexonsmith@apple.com>
Date: Sat, 16 Aug 2014 01:54:37 +0000
Subject: [PATCH] BitcodeReader: Only create one basic block for each
 blockaddress

Block address forward-references are implemented by creating a
`BasicBlock` ahead of time that gets inserted in the `Function` when
it's eventually encountered.

However, if the same blockaddress was used in two separate functions
that were parsed *before* the referenced function (and the blockaddress
was never used at global scope), two separate basic blocks would get
created, one of which would be forgotten creating invalid IR.

This commit changes the forward-reference logic to create only one basic
block (and always return the same blockaddress).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215805 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Bitcode/Reader/BitcodeReader.cpp | 32 +++++++++++++---------------
 lib/Bitcode/Reader/BitcodeReader.h   |  6 +++---
 test/Bitcode/blockaddress.ll         | 14 ++++++++++++
 3 files changed, 32 insertions(+), 20 deletions(-)

diff --git a/lib/Bitcode/Reader/BitcodeReader.cpp b/lib/Bitcode/Reader/BitcodeReader.cpp
index 66426c83c66..e5dfa723b04 100644
--- a/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -1635,11 +1635,14 @@ std::error_code BitcodeReader::ParseConstants() {
       } else {
         // Otherwise insert a placeholder and remember it so it can be inserted
         // when the function is parsed.
-        BB = BasicBlock::Create(Context);
         auto &FwdBBs = BasicBlockFwdRefs[Fn];
         if (FwdBBs.empty())
           BasicBlockFwdRefQueue.push_back(Fn);
-        FwdBBs.emplace_back(BBID, BB);
+        if (FwdBBs.size() < BBID + 1)
+          FwdBBs.resize(BBID + 1);
+        if (!FwdBBs[BBID])
+          FwdBBs[BBID] = BasicBlock::Create(Context);
+        BB = FwdBBs[BBID];
       }
       V = BlockAddress::get(Fn, BB);
       break;
@@ -2392,24 +2395,19 @@ std::error_code BitcodeReader::ParseFunctionBody(Function *F) {
           FunctionBBs[i] = BasicBlock::Create(Context, "", F);
       } else {
         auto &BBRefs = BBFRI->second;
-        std::sort(BBRefs.begin(), BBRefs.end(),
-                  [](const std::pair<unsigned, BasicBlock *> &LHS,
-                     const std::pair<unsigned, BasicBlock *> &RHS) {
-          return LHS.first < RHS.first;
-        });
-        unsigned R = 0, RE = BBRefs.size();
-        for (unsigned I = 0, E = FunctionBBs.size(); I != E; ++I)
-          if (R != RE && BBRefs[R].first == I) {
-            assert(I != 0 && "Invalid reference to entry block");
-            BasicBlock *BB = BBRefs[R++].second;
-            BB->insertInto(F);
-            FunctionBBs[I] = BB;
+        // Check for invalid basic block references.
+        if (BBRefs.size() > FunctionBBs.size())
+          return Error(BitcodeError::InvalidID);
+        assert(!BBRefs.empty() && "Unexpected empty array");
+        assert(!BBRefs.front() && "Invalid reference to entry block");
+        for (unsigned I = 0, E = FunctionBBs.size(), RE = BBRefs.size(); I != E;
+             ++I)
+          if (I < RE && BBRefs[I]) {
+            BBRefs[I]->insertInto(F);
+            FunctionBBs[I] = BBRefs[I];
           } else {
             FunctionBBs[I] = BasicBlock::Create(Context, "", F);
           }
-        // Check for invalid basic block references.
-        if (R != RE)
-          return Error(BitcodeError::InvalidID);
 
         // Erase from the table.
         BasicBlockFwdRefs.erase(BBFRI);
diff --git a/lib/Bitcode/Reader/BitcodeReader.h b/lib/Bitcode/Reader/BitcodeReader.h
index 5bbcaf4c614..6d4e0a2dfe9 100644
--- a/lib/Bitcode/Reader/BitcodeReader.h
+++ b/lib/Bitcode/Reader/BitcodeReader.h
@@ -181,9 +181,9 @@ class BitcodeReader : public GVMaterializer {
   DenseMap<Function*, uint64_t> DeferredFunctionInfo;
 
   /// These are basic blocks forward-referenced by block addresses.  They are
-  /// inserted lazily into functions when they're loaded.
-  typedef std::pair<unsigned, BasicBlock *> BasicBlockRefTy;
-  DenseMap<Function *, std::vector<BasicBlockRefTy>> BasicBlockFwdRefs;
+  /// inserted lazily into functions when they're loaded.  The basic block ID is
+  /// its index into the vector.
+  DenseMap<Function *, std::vector<BasicBlock *>> BasicBlockFwdRefs;
   std::deque<Function *> BasicBlockFwdRefQueue;
 
   /// UseRelativeIDs - Indicates that we are using a new encoding for
diff --git a/test/Bitcode/blockaddress.ll b/test/Bitcode/blockaddress.ll
index 305118c83b8..83fae48bf2f 100644
--- a/test/Bitcode/blockaddress.ll
+++ b/test/Bitcode/blockaddress.ll
@@ -44,3 +44,17 @@ here:
 end:
   ret void
 }
+
+; Check a blockaddress taken in two separate functions before the referenced
+; function.
+define i8* @take1() {
+  ret i8* blockaddress(@taken, %bb)
+}
+define i8* @take2() {
+  ret i8* blockaddress(@taken, %bb)
+}
+define void @taken() {
+  unreachable
+bb:
+  unreachable
+}