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author | Chris Lattner <sabre@nondot.org> | 2003-10-05 04:26:39 +0000 |
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committer | Chris Lattner <sabre@nondot.org> | 2003-10-05 04:26:39 +0000 |
commit | afa060ea3ff93eb99bafd41e593707cee3b9afa3 (patch) | |
tree | cd5a6dcac47a0721196bc5cde2304a8512d757a0 /lib/Transforms/Utils | |
parent | 521c16aadd56503320f61ec0a78ca7fda130ee8f (diff) | |
download | external_llvm-afa060ea3ff93eb99bafd41e593707cee3b9afa3.zip external_llvm-afa060ea3ff93eb99bafd41e593707cee3b9afa3.tar.gz external_llvm-afa060ea3ff93eb99bafd41e593707cee3b9afa3.tar.bz2 |
* Update file header comment
*** Revamp the code which handled unreachable code in the function. Now the
code is much more efficient for high-degree basic blocks, such as those
that occur in the 252.eon SPEC benchmark.
For the interested, the time to promote a SINGLE alloca in _ZN7mrScene4ReadERSi
function used to be > 3.5s. Now it is < .075s. The function has a LOT of
allocas in it, so it appeared to be infinite looping, this should make it much
nicer. :)
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@8863 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/Transforms/Utils')
-rw-r--r-- | lib/Transforms/Utils/PromoteMemoryToRegister.cpp | 108 |
1 files changed, 64 insertions, 44 deletions
diff --git a/lib/Transforms/Utils/PromoteMemoryToRegister.cpp b/lib/Transforms/Utils/PromoteMemoryToRegister.cpp index abfa28b..82d8afc 100644 --- a/lib/Transforms/Utils/PromoteMemoryToRegister.cpp +++ b/lib/Transforms/Utils/PromoteMemoryToRegister.cpp @@ -1,18 +1,10 @@ -//===- PromoteMemoryToRegister.cpp - Convert memory refs to regs ----------===// +//===- PromoteMemoryToRegister.cpp - Convert allocas to registers ---------===// // -// This file is used to promote memory references to be register references. A -// simple example of the transformation performed by this function is: -// -// FROM CODE TO CODE -// %X = alloca int, uint 1 ret int 42 -// store int 42, int *%X -// %Y = load int* %X -// ret int %Y -// -// The code is transformed by looping over all of the alloca instruction, -// calculating dominator frontiers, then inserting phi-nodes following the usual -// SSA construction algorithm. This code does not modify the CFG of the -// function. +// This file promote memory references to be register references. It promotes +// alloca instructions which only have loads and stores as uses. An alloca is +// transformed by using dominator frontiers to place PHI nodes, then traversing +// the function in depth-first order to rewrite loads and stores as appropriate. +// This is just the standard SSA construction algorithm. // //===----------------------------------------------------------------------===// @@ -20,10 +12,8 @@ #include "llvm/Analysis/Dominators.h" #include "llvm/iMemory.h" #include "llvm/iPHINode.h" -#include "llvm/iTerminators.h" #include "llvm/Function.h" #include "llvm/Constant.h" -#include "llvm/Type.h" #include "llvm/Support/CFG.h" #include "Support/StringExtras.h" @@ -139,6 +129,8 @@ void PromoteMem2Reg::run() { // and inserting the phi nodes we marked as necessary // RenamePass(F.begin(), 0, Values); + + // The renamer uses the Visited set to avoid infinite loops. Clear it now. Visited.clear(); // Remove the allocas themselves from the function... @@ -153,6 +145,54 @@ void PromoteMem2Reg::run() { A->replaceAllUsesWith(Constant::getNullValue(A->getType())); A->getParent()->getInstList().erase(A); } + + // At this point, the renamer has added entries to PHI nodes for all reachable + // code. Unfortunately, there may be blocks which are not reachable, which + // the renamer hasn't traversed. If this is the case, the PHI nodes may not + // have incoming values for all predecessors. Loop over all PHI nodes we have + // created, inserting null constants if they are missing any incoming values. + // + for (std::map<BasicBlock*, std::vector<PHINode *> >::iterator I = + NewPhiNodes.begin(), E = NewPhiNodes.end(); I != E; ++I) { + + std::vector<BasicBlock*> Preds(pred_begin(I->first), pred_end(I->first)); + std::vector<PHINode*> &PNs = I->second; + assert(!PNs.empty() && "Empty PHI node list??"); + + // Only do work here if there the PHI nodes are missing incoming values. We + // know that all PHI nodes that were inserted in a block will have the same + // number of incoming values, so we can just check any PHI node. + PHINode *FirstPHI = PNs[0]; + if (Preds.size() != FirstPHI->getNumIncomingValues()) { + // Ok, now we know that all of the PHI nodes are missing entries for some + // basic blocks. Start by sorting the incoming predecessors for efficient + // access. + std::sort(Preds.begin(), Preds.end()); + + // Now we loop through all BB's which have entries in FirstPHI and remove + // them from the Preds list. + for (unsigned i = 0, e = FirstPHI->getNumIncomingValues(); i != e; ++i) { + // Do a log(n) search of teh Preds list for the entry we want. + std::vector<BasicBlock*>::iterator EntIt = + std::lower_bound(Preds.begin(), Preds.end(), + FirstPHI->getIncomingBlock(i)); + assert(EntIt != Preds.end() && *EntIt == FirstPHI->getIncomingBlock(i)&& + "PHI node has entry for a block which is not a predecessor!"); + + // Remove the entry + Preds.erase(EntIt); + } + + // At this point, the blocks left in the preds list must have dummy + // entries inserted into every PHI nodes for the block. + for (unsigned i = 0, e = PNs.size(); i != e; ++i) { + PHINode *PN = PNs[i]; + Value *NullVal = Constant::getNullValue(PN->getType()); + for (unsigned pred = 0, e = Preds.size(); pred != e; ++pred) + PN->addIncoming(NullVal, Preds[pred]); + } + } + } } @@ -169,25 +209,10 @@ bool PromoteMem2Reg::QueuePhiNode(BasicBlock *BB, unsigned AllocaNo) { // Create a PhiNode using the dereferenced type... and add the phi-node to the // BasicBlock. - PHINode *PN = new PHINode(Allocas[AllocaNo]->getAllocatedType(), - Allocas[AllocaNo]->getName() + "." + - utostr(VersionNumbers[AllocaNo]++), - BB->begin()); - - // Add null incoming values for all predecessors. This ensures that if one of - // the predecessors is not found in the depth-first traversal of the CFG (ie, - // because it is an unreachable predecessor), that all PHI nodes will have the - // correct number of entries for their predecessors. - Value *NullVal = Constant::getNullValue(PN->getType()); - - // This is necessary because adding incoming values to the PHI node adds uses - // to the basic blocks being used, which can invalidate the predecessor - // iterator! - std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB)); - for (unsigned i = 0, e = Preds.size(); i != e; ++i) - PN->addIncoming(NullVal, Preds[i]); - - BBPNs[AllocaNo] = PN; + BBPNs[AllocaNo] = new PHINode(Allocas[AllocaNo]->getAllocatedType(), + Allocas[AllocaNo]->getName() + "." + + utostr(VersionNumbers[AllocaNo]++), + BB->begin()); return true; } @@ -202,15 +227,10 @@ void PromoteMem2Reg::RenamePass(BasicBlock *BB, BasicBlock *Pred, std::vector<PHINode *> &BBPNs = BBPNI->second; for (unsigned k = 0; k != BBPNs.size(); ++k) if (PHINode *PN = BBPNs[k]) { - // The PHI node may have multiple entries for this predecessor. We must - // make sure we update all of them. - for (unsigned i = 0, e = PN->getNumOperands(); i != e; i += 2) { - if (PN->getOperand(i+1) == Pred) - // At this point we can assume that the array has phi nodes.. let's - // update the incoming data. - PN->setOperand(i, IncomingVals[k]); - } - // also note that the active variable IS designated by the phi node + // Add this incoming value to the PHI node. + PN->addIncoming(IncomingVals[k], Pred); + + // The currently active variable for this block is now the PHI. IncomingVals[k] = PN; } } |