[llvm-commits] [llvm] r172756 - in /llvm/trunk: include/llvm/Analysis/MemoryBuiltins.h lib/Analysis/MemoryBuiltins.cpp test/Transforms/InstCombine/objsize.ll

Nuno Lopes nunoplopes at sapo.pt
Thu Jan 17 13:46:50 PST 2013


That's interesting...
Thanks for investigating and sorry for the breakage.

Just guessing, I would say that this is a problem related with aliasing, 
since basic AA uses this code. Either that function has some undefined 
behavior that is now being exploited or there's a bug in basic AA.
Unfortunately I won't have time to analyze this problem in the next couple 
of weeks.

Nuno


----- Original Message -----
> Author: void
> Date: Thu Jan 17 15:28:46 2013
> New Revision: 172756
>
> URL: http://llvm.org/viewvc/llvm-project?rev=172756&view=rev
> Log:
> Reverting r171325 & r172363. This was causing a mis-compile on the 
> self-hosted LTO build bots.
>
> Okay, here's how to reproduce the problem:
>
> 1) Build a Release (or Release+Asserts) version of clang in the normal 
> way.
>
> 2) Using the clang & clang++ binaries from (1), build a Release (or
>   Release+Asserts) version of the same sources, but this time enable 
> LTO ---
>   specify the `-flto' flag on the command line.
>
> 3) Run the ARC migrator tests:
>
>    $ arcmt-test --args -triple x86_64-apple-darwin10 -fsyntax-only -x 
> objective-c++ ./src/tools/clang/test/ARCMT/cxx-rewrite.mm
>
> You'll see that the output isn't correct (the whitespace is off).
>
> The mis-compile is in the function `RewriteBuffer::RemoveText' in the
> clang/lib/Rewrite/Core/Rewriter.cpp file. When that function and 
> RewriteRope.cpp
> are compiled with LTO and the `arcmt-test' executable is regenerated, 
> you'll see
> the error. When those files are not LTO'ed, then the output of the 
> `arcmt-test'
> is fine.
>
> It is *really* hard to get a testcase out of this. I'll file a PR with 
> what I
> have currently.
>
> --- Reverse-merging r172363 into '.':
> U    include/llvm/Analysis/MemoryBuiltins.h
> U    lib/Analysis/MemoryBuiltins.cpp
>
> --- Reverse-merging r171325 into '.':
> U    test/Transforms/InstCombine/objsize.ll
> G    include/llvm/Analysis/MemoryBuiltins.h
> G    lib/Analysis/MemoryBuiltins.cpp
>
>
>
> Modified:
>    llvm/trunk/include/llvm/Analysis/MemoryBuiltins.h
>    llvm/trunk/lib/Analysis/MemoryBuiltins.cpp
>    llvm/trunk/test/Transforms/InstCombine/objsize.ll
>
> Modified: llvm/trunk/include/llvm/Analysis/MemoryBuiltins.h
> URL: 
> http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Analysis/MemoryBuiltins.h?rev=172756&r1=172755&r2=172756&view=diff
> ==============================================================================
> --- llvm/trunk/include/llvm/Analysis/MemoryBuiltins.h (original)
> +++ llvm/trunk/include/llvm/Analysis/MemoryBuiltins.h Thu Jan 17 15:28:46 
> 2013
> @@ -153,14 +153,12 @@
> class ObjectSizeOffsetVisitor
>   : public InstVisitor<ObjectSizeOffsetVisitor, SizeOffsetType> {
>
> -  typedef DenseMap<const Value*, SizeOffsetType> CacheMapTy;
> -
>   const DataLayout *TD;
>   const TargetLibraryInfo *TLI;
>   bool RoundToAlign;
>   unsigned IntTyBits;
>   APInt Zero;
> -  CacheMapTy CacheMap;
> +  SmallPtrSet<Instruction *, 8> SeenInsts;
>
>   APInt align(APInt Size, uint64_t Align);
>
>
> Modified: llvm/trunk/lib/Analysis/MemoryBuiltins.cpp
> URL: 
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/MemoryBuiltins.cpp?rev=172756&r1=172755&r2=172756&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Analysis/MemoryBuiltins.cpp (original)
> +++ llvm/trunk/lib/Analysis/MemoryBuiltins.cpp Thu Jan 17 15:28:46 2013
> @@ -385,23 +385,16 @@
>
> SizeOffsetType ObjectSizeOffsetVisitor::compute(Value *V) {
>   V = V->stripPointerCasts();
> +  if (Instruction *I = dyn_cast<Instruction>(V)) {
> +    // If we have already seen this instruction, bail out. Cycles can 
> happen in
> +    // unreachable code after constant propagation.
> +    if (!SeenInsts.insert(I))
> +      return unknown();
>
> -  if (isa<Instruction>(V) || isa<GEPOperator>(V)) {
> -    // return cached value or insert unknown in cache if size of V was 
> not
> -    // computed yet in order to avoid recursions in PHis
> -    std::pair<CacheMapTy::iterator, bool> CacheVal =
> -      CacheMap.insert(std::make_pair(V, unknown()));
> -    if (!CacheVal.second)
> -      return CacheVal.first->second;
> -
> -    SizeOffsetType Result;
>     if (GEPOperator *GEP = dyn_cast<GEPOperator>(V))
> -      Result = visitGEPOperator(*GEP);
> -    else
> -      Result = visit(cast<Instruction>(*V));
> -    return CacheMap[V] = Result;
> +      return visitGEPOperator(*GEP);
> +    return visit(*I);
>   }
> -
>   if (Argument *A = dyn_cast<Argument>(V))
>     return visitArgument(*A);
>   if (ConstantPointerNull *P = dyn_cast<ConstantPointerNull>(V))
> @@ -415,6 +408,8 @@
>   if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
>     if (CE->getOpcode() == Instruction::IntToPtr)
>       return unknown(); // clueless
> +    if (CE->getOpcode() == Instruction::GetElementPtr)
> +      return visitGEPOperator(cast<GEPOperator>(*CE));
>   }
>
>   DEBUG(dbgs() << "ObjectSizeOffsetVisitor::compute() unhandled value: " 
> << *V
> @@ -548,21 +543,9 @@
>   return unknown();
> }
>
> -SizeOffsetType ObjectSizeOffsetVisitor::visitPHINode(PHINode &PHI) {
> -  if (PHI.getNumIncomingValues() == 0)
> -    return unknown();
> -
> -  SizeOffsetType Ret = compute(PHI.getIncomingValue(0));
> -  if (!bothKnown(Ret))
> -    return unknown();
> -
> -  // verify that all PHI incoming pointers have the same size and offset
> -  for (unsigned i = 1, e = PHI.getNumIncomingValues(); i != e; ++i) {
> -    SizeOffsetType EdgeData = compute(PHI.getIncomingValue(i));
> -    if (!bothKnown(EdgeData) || EdgeData != Ret)
> -      return unknown();
> -  }
> -  return Ret;
> +SizeOffsetType ObjectSizeOffsetVisitor::visitPHINode(PHINode&) {
> +  // too complex to analyze statically.
> +  return unknown();
> }
>
> SizeOffsetType ObjectSizeOffsetVisitor::visitSelectInst(SelectInst &I) {
>
> Modified: llvm/trunk/test/Transforms/InstCombine/objsize.ll
> URL: 
> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/objsize.ll?rev=172756&r1=172755&r2=172756&view=diff
> ==============================================================================
> --- llvm/trunk/test/Transforms/InstCombine/objsize.ll (original)
> +++ llvm/trunk/test/Transforms/InstCombine/objsize.ll Thu Jan 17 15:28:46 
> 2013
> @@ -256,131 +256,3 @@
> return:
>   ret i32 7
> }
> -
> -declare noalias i8* @valloc(i32) nounwind
> -
> -; CHECK: @test14
> -; CHECK: ret i32 6
> -define i32 @test14(i32 %a) nounwind {
> -  switch i32 %a, label %sw.default [
> -    i32 1, label %sw.bb
> -    i32 2, label %sw.bb1
> -  ]
> -
> -sw.bb:
> -  %call = tail call noalias i8* @malloc(i32 6) nounwind
> -  br label %sw.epilog
> -
> -sw.bb1:
> -  %call2 = tail call noalias i8* @calloc(i32 3, i32 2) nounwind
> -  br label %sw.epilog
> -
> -sw.default:
> -  %call3 = tail call noalias i8* @valloc(i32 6) nounwind
> -  br label %sw.epilog
> -
> -sw.epilog:
> -  %b.0 = phi i8* [ %call3, %sw.default ], [ %call2, %sw.bb1 ], [ %call, 
> %sw.bb ]
> -  %1 = tail call i32 @llvm.objectsize.i32(i8* %b.0, i1 false)
> -  ret i32 %1
> -}
> -
> -; CHECK: @test15
> -; CHECK: llvm.objectsize
> -define i32 @test15(i32 %a) nounwind {
> -  switch i32 %a, label %sw.default [
> -    i32 1, label %sw.bb
> -    i32 2, label %sw.bb1
> -  ]
> -
> -sw.bb:
> -  %call = tail call noalias i8* @malloc(i32 3) nounwind
> -  br label %sw.epilog
> -
> -sw.bb1:
> -  %call2 = tail call noalias i8* @calloc(i32 2, i32 1) nounwind
> -  br label %sw.epilog
> -
> -sw.default:
> -  %call3 = tail call noalias i8* @valloc(i32 3) nounwind
> -  br label %sw.epilog
> -
> -sw.epilog:
> -  %b.0 = phi i8* [ %call3, %sw.default ], [ %call2, %sw.bb1 ], [ %call, 
> %sw.bb ]
> -  %1 = tail call i32 @llvm.objectsize.i32(i8* %b.0, i1 false)
> -  ret i32 %1
> -}
> -
> -; CHECK: @test16
> -; CHECK: llvm.objectsize
> -define i32 @test16(i8* %a, i32 %n) nounwind {
> -  %b = alloca [5 x i8], align 1
> -  %c = alloca [5 x i8], align 1
> -  switch i32 %n, label %sw.default [
> -    i32 1, label %sw.bb
> -    i32 2, label %sw.bb1
> -  ]
> -
> -sw.bb:
> -  %bp = bitcast [5 x i8]* %b to i8*
> -  br label %sw.epilog
> -
> -sw.bb1:
> -  %cp = bitcast [5 x i8]* %c to i8*
> -  br label %sw.epilog
> -
> -sw.default:
> -  br label %sw.epilog
> -
> -sw.epilog:
> -  %phi = phi i8* [ %a, %sw.default ], [ %cp, %sw.bb1 ], [ %bp, %sw.bb ]
> -  %sz = call i32 @llvm.objectsize.i32(i8* %phi, i1 false)
> -  ret i32 %sz
> -}
> -
> -; CHECK: @test17
> -; CHECK: ret i32 5
> -define i32 @test17(i32 %n) nounwind {
> -  %b = alloca [5 x i8], align 1
> -  %c = alloca [5 x i8], align 1
> -  %bp = bitcast [5 x i8]* %b to i8*
> -  switch i32 %n, label %sw.default [
> -    i32 1, label %sw.bb
> -    i32 2, label %sw.bb1
> -  ]
> -
> -sw.bb:
> -  br label %sw.epilog
> -
> -sw.bb1:
> -  %cp = bitcast [5 x i8]* %c to i8*
> -  br label %sw.epilog
> -
> -sw.default:
> -  br label %sw.epilog
> -
> -sw.epilog:
> -  %phi = phi i8* [ %bp, %sw.default ], [ %cp, %sw.bb1 ], [ %bp, %sw.bb ]
> -  %sz = call i32 @llvm.objectsize.i32(i8* %phi, i1 false)
> -  ret i32 %sz
> -}
> -
> - at globalalias = alias internal [60 x i8]* @a
> -
> -; CHECK: @test18
> -; CHECK-NEXT: ret i32 60
> -define i32 @test18() {
> -  %bc = bitcast [60 x i8]* @globalalias to i8*
> -  %1 = call i32 @llvm.objectsize.i32(i8* %bc, i1 false)
> -  ret i32 %1
> -}
> -
> - at globalalias2 = alias weak [60 x i8]* @a
> -
> -; CHECK: @test19
> -; CHECK: llvm.objectsize
> -define i32 @test19() {
> -  %bc = bitcast [60 x i8]* @globalalias2 to i8*
> -  %1 = call i32 @llvm.objectsize.i32(i8* %bc, i1 false)
> -  ret i32 %1
> -}
>
>
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