RPCS3/llvm-mirror
1
0
Fork 0
mirror of https://github.com/RPCS3/llvm-mirror.git synced 2024-12-29 15:04:57 +00:00
Code Issues Actions Packages Projects Releases Wiki Activity

Simplify code by deleting instructions that preceed unreachable instructions.

Browse Source 
Simplify code by simplifying terminators that branch to blocks that start
with an unreachable instruction.

llvm-svn: 17116
This commit is contained in:
Chris Lattner 2004-10-18 04:07:22 +00:00
parent e058c78728
commit b1827a765a
1 changed files with 101 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

102
lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -21,7 +21,7 @@
#include <algorithm>
#include <functional>
#include <set>
#include <map>
using namespace llvm;
// PropagatePredecessorsForPHIs - This gets "Succ" ready to have the
@ -916,6 +916,106 @@ bool llvm::SimplifyCFG(BasicBlock *BB) {
return SimplifyCFG(BB) | true;
}
}
} else if (isa<UnreachableInst>(BB->getTerminator())) {
// If there are any instructions immediately before the unreachable that can
// be removed, do so.
Instruction *Unreachable = BB->getTerminator();
while (Unreachable != BB->begin()) {
BasicBlock::iterator BBI = Unreachable;
--BBI;
if (isa<CallInst>(BBI)) break;
// Delete this instruction
BB->getInstList().erase(BBI);
Changed = true;
}
// If the unreachable instruction is the first in the block, take a gander
// at all of the predecessors of this instruction, and simplify them.
if (&BB->front() == Unreachable) {
std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB));
for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
TerminatorInst *TI = Preds[i]->getTerminator();
if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
if (BI->isUnconditional()) {
if (BI->getSuccessor(0) == BB) {
new UnreachableInst(TI);
TI->eraseFromParent();
Changed = true;
}
} else {
if (BI->getSuccessor(0) == BB) {
new BranchInst(BI->getSuccessor(1), BI);
BI->eraseFromParent();
} else if (BI->getSuccessor(1) == BB) {
new BranchInst(BI->getSuccessor(0), BI);
BI->eraseFromParent();
Changed = true;
}
}
} else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
if (SI->getSuccessor(i) == BB) {
SI->removeCase(i);
--i; --e;
Changed = true;
}
// If the default value is unreachable, figure out the most popular
// destination and make it the default.
if (SI->getSuccessor(0) == BB) {
std::map<BasicBlock*, unsigned> Popularity;
for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
Popularity[SI->getSuccessor(i)]++;
// Find the most popular block.
unsigned MaxPop = 0;
BasicBlock *MaxBlock = 0;
for (std::map<BasicBlock*, unsigned>::iterator
I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
if (I->second > MaxPop) {
MaxPop = I->second;
MaxBlock = I->first;
}
}
if (MaxBlock) {
// Make this the new default, allowing us to delete any explicit
// edges to it.
SI->setSuccessor(0, MaxBlock);
Changed = true;
for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
if (SI->getSuccessor(i) == MaxBlock) {
SI->removeCase(i);
--i; --e;
}
}
}
} else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
if (II->getUnwindDest() == BB) {
// Convert the invoke to a call instruction. This would be a good
// place to note that the call does not throw though.
BranchInst *BI = new BranchInst(II->getNormalDest(), II);
II->removeFromParent(); // Take out of symbol table
// Insert the call now...
std::vector<Value*> Args(II->op_begin()+3, II->op_end());
CallInst *CI = new CallInst(II->getCalledValue(), Args,
II->getName(), BI);
// If the invoke produced a value, the Call does now instead.
II->replaceAllUsesWith(CI);
delete II;
Changed = true;
}
}
}
// If this block is now dead, remove it.
if (pred_begin(BB) == pred_end(BB)) {
// We know there are no successors, so just nuke the block.
M->getBasicBlockList().erase(BB);
return true;
}
}
}
// Merge basic blocks into their predecessor if there is only one distinct