diff --git a/lib/Transforms/Scalar/LoopRotation.cpp b/lib/Transforms/Scalar/LoopRotation.cpp index e98ae953e53..14c5655f083 100644 --- a/lib/Transforms/Scalar/LoopRotation.cpp +++ b/lib/Transforms/Scalar/LoopRotation.cpp @@ -56,8 +56,8 @@ namespace { } bool runOnLoop(Loop *L, LPPassManager &LPM); - void simplifyLoopLatch(Loop *L); - bool rotateLoop(Loop *L); + bool simplifyLoopLatch(Loop *L); + bool rotateLoop(Loop *L, bool SimplifiedLatch); private: LoopInfo *LI; @@ -84,13 +84,14 @@ bool LoopRotate::runOnLoop(Loop *L, LPPassManager &LPM) { // Simplify the loop latch before attempting to rotate the header // upward. Rotation may not be needed if the loop tail can be folded into the // loop exit. - simplifyLoopLatch(L); + bool SimplifiedLatch = simplifyLoopLatch(L); // One loop can be rotated multiple times. bool MadeChange = false; - while (rotateLoop(L)) + while (rotateLoop(L, SimplifiedLatch)) { MadeChange = true; - + SimplifiedLatch = false; + } return MadeChange; } @@ -212,25 +213,25 @@ static bool shouldSpeculateInstrs(BasicBlock::iterator Begin, /// canonical form so downstream passes can handle it. /// /// I don't believe this invalidates SCEV. -void LoopRotate::simplifyLoopLatch(Loop *L) { +bool LoopRotate::simplifyLoopLatch(Loop *L) { BasicBlock *Latch = L->getLoopLatch(); if (!Latch || Latch->hasAddressTaken()) - return; + return false; BranchInst *Jmp = dyn_cast(Latch->getTerminator()); if (!Jmp || !Jmp->isUnconditional()) - return; + return false; BasicBlock *LastExit = Latch->getSinglePredecessor(); if (!LastExit || !L->isLoopExiting(LastExit)) - return; + return false; BranchInst *BI = dyn_cast(LastExit->getTerminator()); if (!BI) - return; + return false; if (!shouldSpeculateInstrs(Latch->begin(), Jmp)) - return; + return false; DEBUG(dbgs() << "Folding loop latch " << Latch->getName() << " into " << LastExit->getName() << "\n"); @@ -253,10 +254,20 @@ void LoopRotate::simplifyLoopLatch(Loop *L) { if (DominatorTree *DT = getAnalysisIfAvailable()) DT->eraseNode(Latch); Latch->eraseFromParent(); + return true; } /// Rotate loop LP. Return true if the loop is rotated. -bool LoopRotate::rotateLoop(Loop *L) { +/// +/// \param SimplifiedLatch is true if the latch was just folded into the final +/// loop exit. In this case we may want to rotate even though the new latch is +/// now an exiting branch. This rotation would have happened had the latch not +/// been simplified. However, if SimplifiedLatch is false, then we avoid +/// rotating loops in which the latch exits to avoid excessive or endless +/// rotation. LoopRotate should be repeatable and converge to a canonical +/// form. This property is satisfied because simplifying the loop latch can only +/// happen once across multiple invocations of the LoopRotate pass. +bool LoopRotate::rotateLoop(Loop *L, bool SimplifiedLatch) { // If the loop has only one block then there is not much to rotate. if (L->getBlocks().size() == 1) return false; @@ -276,7 +287,12 @@ bool LoopRotate::rotateLoop(Loop *L) { // If the loop latch already contains a branch that leaves the loop then the // loop is already rotated. - if (OrigLatch == 0 || L->isLoopExiting(OrigLatch)) + if (OrigLatch == 0) + return false; + + // Rotate if either the loop latch does *not* exit the loop, or if the loop + // latch was just simplified. + if (L->isLoopExiting(OrigLatch) && !SimplifiedLatch) return false; // Check size of original header and reject loop if it is very big or we can't @@ -505,4 +521,3 @@ bool LoopRotate::rotateLoop(Loop *L) { ++NumRotated; return true; } - diff --git a/test/Transforms/LoopRotate/simplifylatch.ll b/test/Transforms/LoopRotate/simplifylatch.ll index f4227245f74..037bb2042f9 100644 --- a/test/Transforms/LoopRotate/simplifylatch.ll +++ b/test/Transforms/LoopRotate/simplifylatch.ll @@ -1,4 +1,4 @@ -; RUN: opt -S < %s -loop-rotate -verify-dom-info -verify-loop-info | FileCheck %s +; RUN: opt -S < %s -loop-rotate -licm -verify-dom-info -verify-loop-info | FileCheck %s ; PR2624 unroll multiple exits @mode_table = global [4 x i32] zeroinitializer ; <[4 x i32]*> [#uses=1] @@ -37,3 +37,40 @@ bb5: ; preds = %bb2 declare i32 @fegetround() declare void @raise_exception() noreturn + +;CHECK: for.body.lr.ph: +;CHECK-NEXT: %arrayidx1 = getelementptr inbounds i8* %CurPtr, i64 0 +;CHECK-NEXT: %0 = load i8* %arrayidx1, align 1 +;CHECK-NEXT: %conv2 = sext i8 %0 to i32 +;CHECK-NEXT: br label %for.body + +define i32 @foo(i8* %CurPtr, i32 %a) #0 { +entry: + br label %for.cond + +for.cond: ; preds = %for.inc, %entry + %i.0 = phi i32 [ 1, %entry ], [ %inc, %for.inc ] + %cmp = icmp ne i32 %i.0, %a + br i1 %cmp, label %for.body, label %return + +for.body: ; preds = %for.cond + %idxprom = zext i32 %i.0 to i64 + %arrayidx = getelementptr inbounds i8* %CurPtr, i64 %idxprom + %0 = load i8* %arrayidx, align 1 + %conv = sext i8 %0 to i32 + %arrayidx1 = getelementptr inbounds i8* %CurPtr, i64 0 + %1 = load i8* %arrayidx1, align 1 + %conv2 = sext i8 %1 to i32 + %cmp3 = icmp ne i32 %conv, %conv2 + br i1 %cmp3, label %return, label %for.inc + +for.inc: ; preds = %for.body + %inc = add i32 %i.0, 1 + br label %for.cond + +return: ; preds = %for.cond, %for.body + %retval.0 = phi i32 [ 0, %for.body ], [ 1, %for.cond ] + ret i32 %retval.0 +} + +attributes #0 = { nounwind uwtable }