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LoopRotate requires canonical loop form, so it always has preheaders 

and latch blocks.  Reorder entry conditions to make hte pass faster
and more logical.

llvm-svn: 123069
This commit is contained in:
Chris Lattner 2011-01-08 18:06:22 +00:00
parent d62691f4e8
commit 7fab23bc1d
1 changed files with 11 additions and 15 deletions
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26
llvm/lib/Transforms/Scalar/LoopRotation.cpp
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@ -98,29 +98,22 @@ bool LoopRotate::runOnLoop(Loop *L, LPPassManager &LPM) {
/// Rotate loop LP. Return true if the loop is rotated.
bool LoopRotate::rotateLoop(Loop *L) {
BasicBlock *OrigPreHeader = L->getLoopPreheader();
if (!OrigPreHeader) return false;
BasicBlock *OrigLatch = L->getLoopLatch();
if (!OrigLatch) return false;
BasicBlock *OrigHeader = L->getHeader();
// If the loop has only one block then there is not much to rotate.
if (L->getBlocks().size() == 1)
return false;
BasicBlock *OrigHeader = L->getHeader();
BranchInst *BI = dyn_cast<BranchInst>(OrigHeader->getTerminator());
if (BI == 0 || BI->isUnconditional())
return false;
// If the loop header is not one of the loop exiting blocks then
// either this loop is already rotated or it is not
// suitable for loop rotation transformations.
if (!L->isLoopExiting(OrigHeader))
return false;
BranchInst *BI = dyn_cast<BranchInst>(OrigHeader->getTerminator());
if (!BI)
return false;
assert(BI->isConditional() && "Branch Instruction is not conditional");
// Updating PHInodes in loops with multiple exits adds complexity.
// Keep it simple, and restrict loop rotation to loops with one exit only.
// In future, lift this restriction and support for multiple exits if
@ -139,6 +132,9 @@ bool LoopRotate::rotateLoop(Loop *L) {
}
// Now, this loop is suitable for rotation.
BasicBlock *OrigPreHeader = L->getLoopPreheader();
BasicBlock *OrigLatch = L->getLoopLatch();
assert(OrigPreHeader && OrigLatch && "Loop not in canonical form?");
// Anything ScalarEvolution may know about this loop or the PHI nodes
// in its header will soon be invalidated.
@ -300,7 +296,7 @@ bool LoopRotate::rotateLoop(Loop *L) {
// Also, since this original header only has one predecessor, zap its
// PHI nodes, which are now trivial.
FoldSingleEntryPHINodes(OrigHeader);
// TODO: We could just go ahead and merge OrigHeader into its predecessor
// at this point, if we don't mind updating dominator info.