diff options
| -rw-r--r-- | lib/Transforms/Utils/SimplifyCFG.cpp | 43 | ||||
| -rw-r--r-- | test/Transforms/SimplifyCFG/2008-07-13-InfLoopMiscompile.ll | 36 |
2 files changed, 62 insertions, 17 deletions
diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp index bbeac4c..b40537d 100644 --- a/lib/Transforms/Utils/SimplifyCFG.cpp +++ b/lib/Transforms/Utils/SimplifyCFG.cpp @@ -68,11 +68,10 @@ static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred, succ_end(ExistPred) && "ExistPred is not a predecessor of Succ!"); if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do - for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) { - PHINode *PN = cast<PHINode>(I); - Value *V = PN->getIncomingValueForBlock(ExistPred); - PN->addIncoming(V, NewPred); - } + PHINode *PN; + for (BasicBlock::iterator I = Succ->begin(); + (PN = dyn_cast<PHINode>(I)); ++I) + PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred); } // CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an @@ -860,7 +859,7 @@ static bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI) { for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i) if (NewSI->getSuccessor(i) == BB) { if (InfLoopBlock == 0) { - // Insert it at the end of the loop, because it's either code, + // Insert it at the end of the function, because it's either code, // or it won't matter if it's hot. :) InfLoopBlock = BasicBlock::Create("infloop", BB->getParent()); BranchInst::Create(InfLoopBlock, InfLoopBlock); @@ -1430,11 +1429,11 @@ static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) { /// setcc into the predecessor and use logical operations to pick the right /// destination. static bool FoldBranchToCommonDest(BranchInst *BI) { + BasicBlock *BB = BI->getParent(); Instruction *Cond = dyn_cast<Instruction>(BI->getCondition()); if (Cond == 0) return false; - BasicBlock *BB = BI->getParent(); - + // Only allow this if the condition is a simple instruction that can be // executed unconditionally. It must be in the same block as the branch, and // must be at the front of the block. @@ -1456,6 +1455,9 @@ static bool FoldBranchToCommonDest(BranchInst *BI) { for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { BasicBlock *PredBlock = *PI; BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator()); + // Check that we have two conditional branches. If there is a PHI node in + // the common successor, verify that the same value flows in from both + // blocks. if (PBI == 0 || PBI->isUnconditional() || !SafeToMergeTerminators(BI, PBI)) continue; @@ -1596,18 +1598,25 @@ static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) { // Finally, if everything is ok, fold the branches to logical ops. BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1); - // If OtherDest *is* BB, then this is a basic block with just - // a conditional branch in it, where one edge (OtherDesg) goes - // back to the block. We know that the program doesn't get - // stuck in the infinite loop, so the condition must be such - // that OtherDest isn't branched through. Forward to CommonDest, - // and avoid an infinite loop at optimizer time. - if (OtherDest == BB) - OtherDest = CommonDest; - DOUT << "FOLDING BRs:" << *PBI->getParent() << "AND: " << *BI->getParent(); + + // If OtherDest *is* BB, then BB is a basic block with a single conditional + // branch in it, where one edge (OtherDest) goes back to itself but the other + // exits. We don't *know* that the program avoids the infinite loop + // (even though that seems likely). If we do this xform naively, we'll end up + // recursively unpeeling the loop. Since we know that (after the xform is + // done) that the block *is* infinite if reached, we just make it an obviously + // infinite loop with no cond branch. + if (OtherDest == BB) { + // Insert it at the end of the function, because it's either code, + // or it won't matter if it's hot. :) + BasicBlock *InfLoopBlock = BasicBlock::Create("infloop", BB->getParent()); + BranchInst::Create(InfLoopBlock, InfLoopBlock); + OtherDest = InfLoopBlock; + } + DOUT << *PBI->getParent()->getParent(); // BI may have other predecessors. Because of this, we leave diff --git a/test/Transforms/SimplifyCFG/2008-07-13-InfLoopMiscompile.ll b/test/Transforms/SimplifyCFG/2008-07-13-InfLoopMiscompile.ll new file mode 100644 index 0000000..0678e20 --- /dev/null +++ b/test/Transforms/SimplifyCFG/2008-07-13-InfLoopMiscompile.ll @@ -0,0 +1,36 @@ +; RUN: llvm-as < %s | opt -simplifycfg | llvm-dis | grep {%outval = phi i32 .*mux} +; PR2540 +; Outval should end up with a select from 0/2, not all constants. + +target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:32:32" +target triple = "i386-pc-linux-gnu" +@g_37 = common global i32 0 ; <i32*> [#uses=1] +@.str = internal constant [4 x i8] c"%d\0A\00" ; <[4 x i8]*> [#uses=1] + +define i32 @main() nounwind { +entry: + %l = load i32* @g_37, align 4 ; <i32> [#uses=1] + %cmpa = icmp ne i32 %l, 0 ; <i1> [#uses=3] + br i1 %cmpa, label %func_1.exit, label %mooseblock + +mooseblock: ; preds = %entry + %cmpb = icmp eq i1 %cmpa, false ; <i1> [#uses=2] + br i1 %cmpb, label %monkeyblock, label %beeblock + +monkeyblock: ; preds = %monkeyblock, %mooseblock + br i1 %cmpb, label %cowblock, label %monkeyblock + +beeblock: ; preds = %beeblock, %mooseblock + br i1 %cmpa, label %cowblock, label %beeblock + +cowblock: ; preds = %beeblock, %monkeyblock + %cowval = phi i32 [ 2, %beeblock ], [ 0, %monkeyblock ] ; <i32> [#uses=1] + br label %func_1.exit + +func_1.exit: ; preds = %cowblock, %entry + %outval = phi i32 [ %cowval, %cowblock ], [ 1, %entry ] ; <i32> [#uses=1] + %pout = tail call i32 (i8*, ...)* @printf( i8* noalias getelementptr ([4 x i8]* @.str, i32 0, i32 0), i32 %outval ) nounwind ; <i32> [#uses=0] + ret i32 0 +} + +declare i32 @printf(i8*, ...) nounwind |