From ebe807597f3ee67f6c5f9cd462ba325b579a2680 Mon Sep 17 00:00:00 2001 From: Chris Lattner Date: Mon, 24 Dec 2007 19:32:55 +0000 Subject: add a -backedge-hack llc-beta option to codegenprepare. 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 --- lib/Transforms/Scalar/CodeGenPrepare.cpp | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) (limited to 'lib/Transforms') diff --git a/lib/Transforms/Scalar/CodeGenPrepare.cpp b/lib/Transforms/Scalar/CodeGenPrepare.cpp index 7c7352d..f31183c 100644 --- a/lib/Transforms/Scalar/CodeGenPrepare.cpp +++ b/lib/Transforms/Scalar/CodeGenPrepare.cpp @@ -37,6 +37,8 @@ using namespace llvm; namespace { cl::opt OptExtUses("optimize-ext-uses", cl::init(true), cl::Hidden); + // LLCBETA option. + cl::opt 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(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 TIPHIValues; + SmallVector TIPHIValues; // Check to see if Dest has any blocks that can be used as a split edge for // this terminator. -- cgit v1.1