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add a -backedge-hack llc-beta option to codegenprepare.

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When specified, don't split backedges of single-bb loops.
This helps address PR1877



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@45344 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2007-12-24 19:32:55 +00:00
parent 44cb8efdc1
commit ebe807597f
1 changed files with 10 additions and 2 deletions
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12
lib/Transforms/Scalar/CodeGenPrepare.cpp
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@ -37,6 +37,8 @@ using namespace llvm;
namespace {
cl::opt<bool> OptExtUses("optimize-ext-uses",
cl::init(true), cl::Hidden);
// LLCBETA option.
cl::opt<bool> DontHackBackedge("backedge-hack", cl::Hidden);
}
namespace {
@ -264,7 +266,7 @@ void CodeGenPrepare::EliminateMostlyEmptyBlock(BasicBlock *BB) {
}
/// SplitEdgeNicely - Split the critical edge from TI to it's specified
/// SplitEdgeNicely - Split the critical edge from TI to its specified
/// successor if it will improve codegen. We only do this if the successor has
/// phi nodes (otherwise critical edges are ok). If there is already another
/// predecessor of the succ that is empty (and thus has no phi nodes), use it
@ -275,9 +277,15 @@ static void SplitEdgeNicely(TerminatorInst *TI, unsigned SuccNum, Pass *P) {
assert(isa<PHINode>(Dest->begin()) &&
"This should only be called if Dest has a PHI!");
// As a hack, never split backedges of loops. Even though the copy for any
// PHIs inserted on the backedge would be dead for exits from the loop, we
// assume that the cost of *splitting* the backedge would be too high.
if (DontHackBackedge && Dest == TIBB)
return;
/// TIPHIValues - This array is lazily computed to determine the values of
/// PHIs in Dest that TI would provide.
std::vector<Value*> TIPHIValues;
SmallVector<Value*, 32> TIPHIValues;
// Check to see if Dest has any blocks that can be used as a split edge for
// this terminator.