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add a debugging option to help track down j-t problems.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@60514 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2008-12-04 00:07:59 +00:00
parent cef874ae2b
commit 77ee977fcf
1 changed files with 14 additions and 1 deletions
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15
lib/Transforms/Scalar/JumpThreading.cpp
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@ -36,6 +36,11 @@ Threshold("jump-threading-threshold",
cl::desc("Max block size to duplicate for jump threading"),
cl::init(6), cl::Hidden);
static cl::opt<int>
DebugIterations("jump-threading-debug",
cl::desc("Stop jump threading after N iterations"),
cl::init(-1), cl::Hidden);
namespace {
/// This pass performs 'jump threading', which looks at blocks that have
/// multiple predecessors and multiple successors. If one or more of the
@ -104,11 +109,15 @@ bool JumpThreading::runOnFunction(Function &F) {
// If the block is trivially dead, zap it. This eliminates the successor
// edges which simplifies the CFG.
if (pred_begin(BB) == pred_end(BB) &&
BB != &BB->getParent()->getEntryBlock()) {
BB != &BB->getParent()->getEntryBlock() &&
DebugIterations != 0) {
DOUT << " JT: Deleting dead block '" << BB->getNameStart()
<< "' with terminator: " << *BB->getTerminator();
DeleteDeadBlock(BB);
Changed = true;
if (DebugIterations != -1)
DebugIterations = DebugIterations-1;
}
}
AnotherIteration = Changed;
@ -183,6 +192,10 @@ static unsigned getJumpThreadDuplicationCost(const BasicBlock *BB) {
/// ProcessBlock - If there are any predecessors whose control can be threaded
/// through to a successor, transform them now.
bool JumpThreading::ProcessBlock(BasicBlock *BB) {
if (DebugIterations == 0) return false;
if (DebugIterations != -1)
DebugIterations = DebugIterations-1;
// If this block has a single predecessor, and if that pred has a single
// successor, merge the blocks. This encourages recursive jump threading
// because now the condition in this block can be threaded through