From 31b941a60dc0e2cb1598673c1d85e01d0df02ae6 Mon Sep 17 00:00:00 2001 From: Andrew Trick Date: Fri, 2 Sep 2011 17:26:28 +0000 Subject: [PATCH] Enable SCEV-based unrolling by default. This changes loop unrolling to use the same mechanism for trip count computation as indvars. This is a stronger check that tends to unroll more loops. A very common side-effect is that many single iteration loops will be removed sooner. The real goal was simply to remove dependence on canonical IVs. x86 is break even. ARM performance changes to expect (+ is good): External/SPEC/CFP2000/183.equake/183.equake +13% SingleSource/Benchmarks/Dhrystone/fldry +21% MultiSource/Applications/spiff/spiff +3% SingleSource/Benchmarks/Stanford/Puzzle -14% The Puzzle regression is actually an improvement in loop optimization that defeats GVN: rdar://problem/10065079. llvm-svn: 139009 --- llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp index dab3ac42eaf4..cca7ba0bd4e4 100644 --- a/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp +++ b/llvm/lib/Transforms/Scalar/LoopUnrollPass.cpp @@ -39,9 +39,9 @@ UnrollAllowPartial("unroll-allow-partial", cl::init(false), cl::Hidden, cl::desc("Allows loops to be partially unrolled until " "-unroll-threshold loop size is reached.")); -// Temporary flag to be made default shortly. +// Temporary flag to be removed in 3.0 static cl::opt -UnrollWithSCEV("unroll-scev", cl::init(false), cl::Hidden, +NoSCEVUnroll("disable-unroll-scev", cl::init(false), cl::Hidden, cl::desc("Use ScalarEvolution to analyze loop trip counts for unrolling")); namespace { @@ -145,7 +145,7 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) { // Find trip count and trip multiple if count is not available unsigned TripCount = 0; unsigned TripMultiple = 1; - if (UnrollWithSCEV) { + if (!NoSCEVUnroll) { // Find "latch trip count". UnrollLoop assumes that control cannot exit // via the loop latch on any iteration prior to TripCount. The loop may exit // early via an earlier branch.