From 3eada319fc21bca31a2bc7819e4c05f46e6f82e1 Mon Sep 17 00:00:00 2001 From: Andrew Trick Date: Wed, 11 Jan 2012 06:52:55 +0000 Subject: Clarified the SCEV getSmallConstantTripCount interface with in-your-face comments. This interface is misleading and dangerous, but it is actually what we need for unrolling. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@147926 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Analysis/ScalarEvolution.cpp | 27 ++++++++++++++++++--------- 1 file changed, 18 insertions(+), 9 deletions(-) (limited to 'lib/Analysis/ScalarEvolution.cpp') diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp index 1fe72fd2b9..008f259573 100644 --- a/lib/Analysis/ScalarEvolution.cpp +++ b/lib/Analysis/ScalarEvolution.cpp @@ -3939,13 +3939,19 @@ const SCEV *ScalarEvolution::createSCEV(Value *V) { // /// getSmallConstantTripCount - Returns the maximum trip count of this loop as a -/// normal unsigned value, if possible. Returns 0 if the trip count is unknown -/// or not constant. Will also return 0 if the maximum trip count is very large -/// (>= 2^32) -unsigned ScalarEvolution::getSmallConstantTripCount(Loop *L, - BasicBlock *ExitBlock) { +/// normal unsigned value. Returns 0 if the trip count is unknown or not +/// constant. Will also return 0 if the maximum trip count is very large (>= +/// 2^32). +/// +/// This "trip count" assumes that control exits via ExitingBlock. More +/// precisely, it is the number of times that control may reach ExitingBlock +/// before taking the branch. For loops with multiple exits, it may not be the +/// number times that the loop header executes because the loop may exit +/// prematurely via another branch. +unsigned ScalarEvolution:: +getSmallConstantTripCount(Loop *L, BasicBlock *ExitingBlock) { const SCEVConstant *ExitCount = - dyn_cast(getExitCount(L, ExitBlock)); + dyn_cast(getExitCount(L, ExitingBlock)); if (!ExitCount) return 0; @@ -3968,9 +3974,12 @@ unsigned ScalarEvolution::getSmallConstantTripCount(Loop *L, /// multiple of a constant (which is also the case if the trip count is simply /// constant, use getSmallConstantTripCount for that case), Will also return 1 /// if the trip count is very large (>= 2^32). -unsigned ScalarEvolution::getSmallConstantTripMultiple(Loop *L, - BasicBlock *ExitBlock) { - const SCEV *ExitCount = getExitCount(L, ExitBlock); +/// +/// As explained in the comments for getSmallConstantTripCount, this assumes +/// that control exits the loop via ExitingBlock. +unsigned ScalarEvolution:: +getSmallConstantTripMultiple(Loop *L, BasicBlock *ExitingBlock) { + const SCEV *ExitCount = getExitCount(L, ExitingBlock); if (ExitCount == getCouldNotCompute()) return 1; -- cgit v1.2.3-18-g5258