diff --git a/lib/Transforms/Utils/LoopSimplify.cpp b/lib/Transforms/Utils/LoopSimplify.cpp index 7289f2261a6..a4526e26613 100644 --- a/lib/Transforms/Utils/LoopSimplify.cpp +++ b/lib/Transforms/Utils/LoopSimplify.cpp @@ -168,6 +168,8 @@ bool LoopSimplify::runOnFunction(Function &F) { /// bool LoopSimplify::ProcessLoop(Loop *L) { bool Changed = false; +ReprocessLoop: + // Canonicalize inner loops before outer loops. Inner loop canonicalization // can provide work for the outer loop to canonicalize. for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I) @@ -208,16 +210,25 @@ bool LoopSimplify::ProcessLoop(Loop *L) { // If the header has more than two predecessors at this point (from the // preheader and from multiple backedges), we must adjust the loop. - if (L->getNumBackEdges() != 1) { - - // If this is really a nested loop, rip it out into a child loop. - if (Loop *NL = SeparateNestedLoop(L)) { - ++NumNested; - // This is a big restructuring change, reprocess the whole loop. - ProcessLoop(NL); - return true; + unsigned NumBackedges = L->getNumBackEdges(); + if (NumBackedges != 1) { + // If this is really a nested loop, rip it out into a child loop. Don't do + // this for loops with a giant number of backedges, just factor them into a + // common backedge instead. + if (NumBackedges < 8) { + if (Loop *NL = SeparateNestedLoop(L)) { + ++NumNested; + // This is a big restructuring change, reprocess the whole loop. + ProcessLoop(NL); + Changed = true; + // GCC doesn't tail recursion eliminate this. + goto ReprocessLoop; + } } + // If we either couldn't, or didn't want to, identify nesting of the loops, + // insert a new block that all backedges target, then make it jump to the + // loop header. InsertUniqueBackedgeBlock(L); NumInserted++; Changed = true;