diff options
Diffstat (limited to 'llvm/lib')
| -rw-r--r-- | llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp | 38 |
1 files changed, 23 insertions, 15 deletions
diff --git a/llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp b/llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp index a87f8504bfb..828d6a173bb 100644 --- a/llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp +++ b/llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp @@ -425,14 +425,17 @@ static bool rewriteSingleStoreAlloca(AllocaInst *AI, AllocaInfo &Info, /// using the Alloca. /// /// If we cannot promote this alloca (because it is read before it is written), -/// return true. This is necessary in cases where, due to control flow, the -/// alloca is potentially undefined on some control flow paths. e.g. code like -/// this is potentially correct: -/// -/// for (...) { if (c) { A = undef; undef = B; } } -/// -/// ... so long as A is not used before undef is set. -static void promoteSingleBlockAlloca(AllocaInst *AI, const AllocaInfo &Info, +/// return false. This is necessary in cases where, due to control flow, the +/// alloca is undefined only on some control flow paths. e.g. code like +/// this is correct in LLVM IR: +/// // A is an alloca with no stores so far +/// for (...) { +/// int t = *A; +/// if (!first_iteration) +/// use(t); +/// *A = 42; +/// } +static bool promoteSingleBlockAlloca(AllocaInst *AI, const AllocaInfo &Info, LargeBlockInfo &LBI, AliasSetTracker *AST) { // The trickiest case to handle is when we have large blocks. Because of this, @@ -467,10 +470,15 @@ static void promoteSingleBlockAlloca(AllocaInst *AI, const AllocaInfo &Info, std::make_pair(LoadIdx, static_cast<StoreInst *>(nullptr)), less_first()); - - if (I == StoresByIndex.begin()) - // If there is no store before this load, the load takes the undef value. - LI->replaceAllUsesWith(UndefValue::get(LI->getType())); + if (I == StoresByIndex.begin()) { + if (StoresByIndex.empty()) + // If there are no stores, the load takes the undef value. + LI->replaceAllUsesWith(UndefValue::get(LI->getType())); + else + // There is no store before this load, bail out (load may be affected + // by the following stores - see main comment). + return false; + } else // Otherwise, there was a store before this load, the load takes its value. LI->replaceAllUsesWith(std::prev(I)->second->getOperand(0)); @@ -506,6 +514,7 @@ static void promoteSingleBlockAlloca(AllocaInst *AI, const AllocaInfo &Info, } ++NumLocalPromoted; + return true; } void PromoteMem2Reg::run() { @@ -557,9 +566,8 @@ void PromoteMem2Reg::run() { // If the alloca is only read and written in one basic block, just perform a // linear sweep over the block to eliminate it. - if (Info.OnlyUsedInOneBlock) { - promoteSingleBlockAlloca(AI, Info, LBI, AST); - + if (Info.OnlyUsedInOneBlock && + promoteSingleBlockAlloca(AI, Info, LBI, AST)) { // The alloca has been processed, move on. RemoveFromAllocasList(AllocaNum); continue; |
