[llvm] r207713 - Patch for function cloning to inline all blocks whose address is taken
Eric Christopher
echristo at gmail.com
Thu May 1 11:03:39 PDT 2014
It's not particularly possible to test it. I had the discussion with
Gerolf there a bit. It mostly relies on being able to inline things
that right now we wouldn't be able to without better escape analysis.
I think the bug is real which is why I finally said ok. :\
-eric
On Wed, Apr 30, 2014 at 9:11 PM, Rafael Espíndola
<rafael.espindola at gmail.com> wrote:
> is it possible to test this?
>
> On 30 April 2014 18:05, Gerolf Hoflehner <ghoflehner at apple.com> wrote:
>> Author: ghoflehner
>> Date: Wed Apr 30 17:05:02 2014
>> New Revision: 207713
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=207713&view=rev
>> Log:
>> Patch for function cloning to inline all blocks whose address is taken
>>
>> Not all address taken blocks get inlined. The reason is
>> that a blocks new address is known only when it is cloned. But e.g.
>> a branch instruction in a different block could need that address earlier
>> while it gets cloned. The solution is to collect the set of all
>> blocks that can potentially get inlined and compute a new block address
>> up front. Then clone and cleanup.
>>
>> rdar://16427209
>>
>> Modified:
>> llvm/trunk/lib/Transforms/Utils/CloneFunction.cpp
>>
>> Modified: llvm/trunk/lib/Transforms/Utils/CloneFunction.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/CloneFunction.cpp?rev=207713&r1=207712&r2=207713&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/Transforms/Utils/CloneFunction.cpp (original)
>> +++ llvm/trunk/lib/Transforms/Utils/CloneFunction.cpp Wed Apr 30 17:05:02 2014
>> @@ -32,6 +32,7 @@
>> #include "llvm/Transforms/Utils/Local.h"
>> #include "llvm/Transforms/Utils/ValueMapper.h"
>> #include <map>
>> +#include <set>
>> using namespace llvm;
>>
>> // CloneBasicBlock - See comments in Cloning.h
>> @@ -272,42 +273,36 @@ namespace {
>> NameSuffix(nameSuffix), CodeInfo(codeInfo), DL(DL) {
>> }
>>
>> - /// CloneBlock - The specified block is found to be reachable, clone it and
>> - /// anything that it can reach.
>> + /// CloneBlock - The specified block is found to be reachable, so clone it
>> + /// into NewBB.
>> + /// ToClone is the vector of actually cloned blocks.
>> + /// OrigBBs is the set of all blocks reacheable from the entry block.
>> + /// It contains the block candidates and makes sure each block
>> + /// is cloned at most once.
>> void CloneBlock(const BasicBlock *BB,
>> - std::vector<const BasicBlock*> &ToClone);
>> + BasicBlock *NewBB,
>> + std::vector<const BasicBlock *> &ToClone,
>> + std::set<const BasicBlock *> &OrigBBs);
>> };
>> }
>>
>> -/// CloneBlock - The specified block is found to be reachable, clone it and
>> -/// anything that it can reach.
>> +/// CloneBlock - The specified block is found to be reachable, so clone it
>> +/// into NewBB.
>> +/// ToClone is the vector of actually cloned blocks.
>> +/// OrigBBs is the set of all blocks reacheable from the entry block.
>> +/// It contains the block candidates and makes sure each block
>> +/// is cloned at most once.
>> void PruningFunctionCloner::CloneBlock(const BasicBlock *BB,
>> - std::vector<const BasicBlock*> &ToClone){
>> - WeakVH &BBEntry = VMap[BB];
>> -
>> - // Have we already cloned this block?
>> - if (BBEntry) return;
>> + BasicBlock *NewBB,
>> + std::vector<const BasicBlock *> &ToClone,
>> + std::set<const BasicBlock *> &OrigBBs) {
>>
>> - // Nope, clone it now.
>> - BasicBlock *NewBB;
>> - BBEntry = NewBB = BasicBlock::Create(BB->getContext());
>> - if (BB->hasName()) NewBB->setName(BB->getName()+NameSuffix);
>> + // Remove BB from list of blocks to clone.
>> + // When it was not in the list, it has been cloned already, so
>> + // don't clone again.
>> + if (!OrigBBs.erase(BB)) return;
>>
>> - // It is only legal to clone a function if a block address within that
>> - // function is never referenced outside of the function. Given that, we
>> - // want to map block addresses from the old function to block addresses in
>> - // the clone. (This is different from the generic ValueMapper
>> - // implementation, which generates an invalid blockaddress when
>> - // cloning a function.)
>> - //
>> - // Note that we don't need to fix the mapping for unreachable blocks;
>> - // the default mapping there is safe.
>> - if (BB->hasAddressTaken()) {
>> - Constant *OldBBAddr = BlockAddress::get(const_cast<Function*>(OldFunc),
>> - const_cast<BasicBlock*>(BB));
>> - VMap[OldBBAddr] = BlockAddress::get(NewFunc, NewBB);
>> - }
>> -
>> + // Nope, clone it now.
>>
>> bool hasCalls = false, hasDynamicAllocas = false, hasStaticAllocas = false;
>>
>> @@ -425,7 +420,7 @@ void llvm::CloneAndPruneFunctionInto(Fun
>> const DataLayout *DL,
>> Instruction *TheCall) {
>> assert(NameSuffix && "NameSuffix cannot be null!");
>> -
>> +
>> #ifndef NDEBUG
>> for (Function::const_arg_iterator II = OldFunc->arg_begin(),
>> E = OldFunc->arg_end(); II != E; ++II)
>> @@ -435,15 +430,91 @@ void llvm::CloneAndPruneFunctionInto(Fun
>> PruningFunctionCloner PFC(NewFunc, OldFunc, VMap, ModuleLevelChanges,
>> NameSuffix, CodeInfo, DL);
>>
>> - // Clone the entry block, and anything recursively reachable from it.
>> + // Since all BB address references need to be known before block-by-block
>> + // processing, we need to create all reachable blocks before processing
>> + // them for instruction cloning and pruning. Some of these blocks may
>> + // be removed due to later pruning.
>> std::vector<const BasicBlock*> CloneWorklist;
>> + //
>> + // OrigBBs consists of all blocks reachable from the entry
>> + // block.
>> + // This list will be pruned down by the CloneFunction() due to two
>> + // two optimizations:
>> + // First, when a conditional branch target is known at compile-time,
>> + // only the actual branch destination block needs to be cloned.
>> + // Second, when a switch statement target is known at compile-time,
>> + // only the actual case statement needs to be cloned.
>> + std::set<const BasicBlock *> OrigBBs;
>> +
>> + CloneWorklist.push_back(&OldFunc->getEntryBlock());
>> + while (!CloneWorklist.empty()) {
>> + const BasicBlock *BB = CloneWorklist.back();
>> + CloneWorklist.pop_back();
>> +
>> + // Don't revisit blocks.
>> + if (VMap.count(BB))
>> + continue;
>> +
>> + BasicBlock *NewBB = BasicBlock::Create(BB->getContext());
>> + if (BB->hasName())
>> + NewBB->setName(BB->getName() + NameSuffix);
>> +
>> + // It is legal to clone a function when a block address within that
>> + // function is never escapes outside of the function. Given that, we
>> + // want to map block addresses from the old function to block addresses in
>> + // the clone. (This is different from the generic ValueMapper
>> + // implementation, which generates an invalid block address when
>> + // cloning a function.)
>> + // Note the current escape address does not catch all legal cases: even
>> + // when all block addresses taken are local and the function has the
>> + // always_inline attribute due to the indirect branch inlining is
>> + // suppressed.
>> + // Note that we don't need to fix the mapping for unreachable blocks;
>> + // the default mapping there is safe.
>> + if (BB->hasAddressTaken()) {
>> + Constant *OldBBAddr = BlockAddress::get(const_cast<Function*>(OldFunc),
>> + const_cast<BasicBlock*>(BB));
>> + VMap[OldBBAddr] = BlockAddress::get(NewFunc, NewBB);
>> + }
>> +
>> + OrigBBs.insert(BB);
>> + VMap[BB] = NewBB;
>> + // Iterate over all possible successors and add them to the CloneWorklist.
>> + const TerminatorInst *Term = BB->getTerminator();
>> + for (unsigned i = 0, e = Term->getNumSuccessors(); i != e; ++i) {
>> + BasicBlock *Succ = Term->getSuccessor(i);
>> + CloneWorklist.push_back(Succ);
>> + }
>> + }
>> +
>> + // Now, fill only the reachable blocks with the cloned contents
>> + // of the originals.
>> + assert(CloneWorklist.empty() && "Dirty worklist before re-use\n");
>> CloneWorklist.push_back(&OldFunc->getEntryBlock());
>> while (!CloneWorklist.empty()) {
>> const BasicBlock *BB = CloneWorklist.back();
>> CloneWorklist.pop_back();
>> - PFC.CloneBlock(BB, CloneWorklist);
>> + PFC.CloneBlock(BB, cast<BasicBlock>(VMap[BB]), CloneWorklist,
>> + OrigBBs);
>> }
>> -
>> +
>> + // FIXME: Delete BB's that were created but have been pruned.
>> + // Actual cloning may have found pruning opportunities since
>> + // branch or switch statement target may have been known at compile-time.
>> + // Alternatively we could write a routine CloneFunction and add a) a
>> + // parameter to actually do the cloning and b) a return parameter that
>> + // gives a list of blocks that need to be cloned also. Then we could
>> + // call CloneFunction when we collect the blocks to clone, but suppress
>> + // cloning. And then actually *do* the cloning in the while loop above. Then
>> + // the cleanup here would become redundant, and so would be the OrigBBs.
>> + for (std::set<const BasicBlock *>::iterator Oi = OrigBBs.begin(),
>> + Oe = OrigBBs.end(); Oi != Oe; ++Oi) {
>> + const BasicBlock *Orig = *Oi;
>> + BasicBlock *NewBB = cast<BasicBlock>(VMap[Orig]);
>> + delete NewBB;
>> + VMap[Orig] = 0;
>> + }
>> +
>> // Loop over all of the basic blocks in the old function. If the block was
>> // reachable, we have cloned it and the old block is now in the value map:
>> // insert it into the new function in the right order. If not, ignore it.
>> @@ -454,7 +525,8 @@ void llvm::CloneAndPruneFunctionInto(Fun
>> BI != BE; ++BI) {
>> Value *V = VMap[BI];
>> BasicBlock *NewBB = cast_or_null<BasicBlock>(V);
>> - if (!NewBB) continue; // Dead block.
>> + if (!NewBB)
>> + continue; // Dead block.
>>
>> // Add the new block to the new function.
>> NewFunc->getBasicBlockList().push_back(NewBB);
>>
>>
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