[llvm-commits] [llvm] r53533 - in /llvm/trunk: lib/Transforms/Utils/SimplifyCFG.cpp test/Transforms/SimplifyCFG/2008-07-13-InfLoopMiscompile.ll
Chris Lattner
sabre at nondot.org
Sun Jul 13 15:23:11 PDT 2008
Author: lattner
Date: Sun Jul 13 17:23:11 2008
New Revision: 53533
URL: http://llvm.org/viewvc/llvm-project?rev=53533&view=rev
Log:
Fix mishandling of the infinite loop case when merging two blocks. This
fixes PR2540.
Added:
llvm/trunk/test/Transforms/SimplifyCFG/2008-07-13-InfLoopMiscompile.ll
Modified:
llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
Modified: llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp?rev=53533&r1=53532&r2=53533&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp Sun Jul 13 17:23:11 2008
@@ -68,11 +68,10 @@
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 @@
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 @@
/// 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 @@
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 @@
// 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
Added: llvm/trunk/test/Transforms/SimplifyCFG/2008-07-13-InfLoopMiscompile.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SimplifyCFG/2008-07-13-InfLoopMiscompile.ll?rev=53533&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/SimplifyCFG/2008-07-13-InfLoopMiscompile.ll (added)
+++ llvm/trunk/test/Transforms/SimplifyCFG/2008-07-13-InfLoopMiscompile.ll Sun Jul 13 17:23:11 2008
@@ -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"
+ at g_37 = common global i32 0 ; <i32*> [#uses=1]
+ at .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
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