From 5a5fd7b1b33be5f6c83bf5eda08e0d053805c7da 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: 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).

llvm-svn: 215805
---
 llvm/lib/Bitcode/Reader/BitcodeReader.cpp | 32 +++++++++++++++----------------
 1 file changed, 15 insertions(+), 17 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 66426c8..e5dfa72 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/llvm/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);
-- 
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