[llvm] r207713 - Patch for function cloning to inline all blocks whose address is taken
Gerolf Hoflehner
ghoflehner at apple.com
Wed Apr 30 15:05:03 PDT 2014
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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