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Fix loop unswitching's assumption that a code path which either

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infinite loops or exits will eventually exit. This fixes PR5373.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112745 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman
2010-09-01 21:46:45 +00:00
parent 6e3665bcd0
commit b0a57210a4
2 changed files with 61 additions and 9 deletions
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17
lib/Transforms/Scalar/LoopUnswitch.cpp
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@@ -277,19 +277,18 @@ bool LoopUnswitch::processCurrentLoop() {
return Changed;
}
/// isTrivialLoopExitBlock - Check to see if all paths from BB either:
/// 1. Exit the loop with no side effects.
/// 2. Branch to the latch block with no side-effects.
/// isTrivialLoopExitBlock - Check to see if all paths from BB exit the
/// loop with no side effects (including infinite loops).
///
/// If these conditions are true, we return true and set ExitBB to the block we
/// If true, we return true and set ExitBB to the block we
/// exit through.
///
static bool isTrivialLoopExitBlockHelper(Loop *L, BasicBlock *BB,
BasicBlock *&ExitBB,
std::set<BasicBlock*> &Visited) {
if (!Visited.insert(BB).second) {
// Already visited and Ok, end of recursion.
return true;
// Already visited. Without more analysis, this could indicate an infinte loop.
return false;
} else if (!L->contains(BB)) {
// Otherwise, this is a loop exit, this is fine so long as this is the
// first exit.
@@ -319,7 +318,7 @@ static bool isTrivialLoopExitBlockHelper(Loop *L, BasicBlock *BB,
/// process. If so, return the block that is exited to, otherwise return null.
static BasicBlock *isTrivialLoopExitBlock(Loop *L, BasicBlock *BB) {
std::set<BasicBlock*> Visited;
Visited.insert(L->getHeader()); // Branches to header are ok.
Visited.insert(L->getHeader()); // Branches to header make infinite loops.
BasicBlock *ExitBB = 0;
if (isTrivialLoopExitBlockHelper(L, BB, ExitBB, Visited))
return ExitBB;
@@ -351,8 +350,8 @@ bool LoopUnswitch::IsTrivialUnswitchCondition(Value *Cond, Constant **Val,
if (!BI->isConditional() || BI->getCondition() != Cond)
return false;
// Check to see if a successor of the branch is guaranteed to go to the
// latch block or exit through a one exit block without having any
// Check to see if a successor of the branch is guaranteed to
// exit through a unique exit block without having any
// side-effects. If so, determine the value of Cond that causes it to do
// this.
if ((LoopExitBB = isTrivialLoopExitBlock(currentLoop,