[llvm] r247972 - Simplify SmallBitVector::applyMask by consolidating common code for 32-bit and 64-bit builds.

[Aaron Ballman via llvm-commits]

On Fri, Sep 18, 2015 at 8:37 AM, Yaron Keren <yaron.keren at gmail.com> wrote:
> Thanks, this code will not be reached in 32 bits as the assert will fail but
> that won't hold in release config, the shift code should probably be in a
> conditional of both NumBaseBits and MaskWords, as was the original code. It
> should be still possible to merge them but more carefully.

In theory, the code doesn't have to be reached for UB to cause
problems anyway. I wasn't certain that upcasting to 64-bits was the
right approach either, that's why I punted on just fixing it myself.
It still seems like it is solvable though.

~Aaron

>
>
> 2015-09-18 15:20 GMT+03:00 Aaron Ballman <aaron at aaronballman.com>:
>>
>> On Fri, Sep 18, 2015 at 2:35 AM, Yaron Keren via llvm-commits
>> <llvm-commits at lists.llvm.org> wrote:
>> > Author: yrnkrn
>> > Date: Fri Sep 18 01:35:12 2015
>> > New Revision: 247972
>> >
>> > URL: http://llvm.org/viewvc/llvm-project?rev=247972&view=rev
>> > Log:
>> > Simplify SmallBitVector::applyMask by consolidating common code for
>> > 32-bit and 64-bit builds.
>> > Extend mask value to 64 bits before taking its complement and assert
>> > when mask is
>> > too large to apply in the small case (previously the extra words were
>> > silently ignored).
>> >
>> > http://reviews.llvm.org/D11890
>> >
>> > Patch by James Touton!
>> >
>> >
>> > Modified:
>> >     llvm/trunk/include/llvm/ADT/SmallBitVector.h
>> >     llvm/trunk/unittests/ADT/BitVectorTest.cpp
>> >
>> > Modified: llvm/trunk/include/llvm/ADT/SmallBitVector.h
>> > URL:
>> > http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/SmallBitVector.h?rev=247972&r1=247971&r2=247972&view=diff
>> >
>> > ==============================================================================
>> > --- llvm/trunk/include/llvm/ADT/SmallBitVector.h (original)
>> > +++ llvm/trunk/include/llvm/ADT/SmallBitVector.h Fri Sep 18 01:35:12
>> > 2015
>> > @@ -553,17 +553,15 @@ public:
>> >  private:
>> >    template<bool AddBits, bool InvertMask>
>> >    void applyMask(const uint32_t *Mask, unsigned MaskWords) {
>> > -    if (NumBaseBits == 64 && MaskWords >= 2) {
>> > -      uint64_t M = Mask[0] | (uint64_t(Mask[1]) << 32);
>> > -      if (InvertMask) M = ~M;
>> > -      if (AddBits) setSmallBits(getSmallBits() | M);
>> > -      else         setSmallBits(getSmallBits() & ~M);
>> > -    } else {
>> > -      uint32_t M = Mask[0];
>> > -      if (InvertMask) M = ~M;
>> > -      if (AddBits) setSmallBits(getSmallBits() | M);
>> > -      else         setSmallBits(getSmallBits() & ~M);
>> > +    uintptr_t M = Mask[0];
>> > +    if (MaskWords != 1) {
>> > +      assert(NumBaseBits == 64 && MaskWords == 2 &&
>> > +             "Mask is larger than base!");
>> > +      M |= uintptr_t(Mask[1]) << 32;
>>
>> This patch introduces undefined behavior on platforms where uintptr_t
>> is 32-bits, such as on Windows when compiling with MSVC in 23-bit
>> mode.
>>
>> 67>E:\llvm\llvm\include\llvm/ADT/SmallBitVector.h(560): warning C4293:
>> '<<': shift count negative or too big, undefined behavior (compiling
>> source file
>> E:\llvm\llvm\tools\clang\lib\StaticAnalyzer\Core\FunctionSummary.cpp)
>> 67>  E:\llvm\llvm\include\llvm/ADT/SmallBitVector.h(521): note: see
>> reference to function template instantiation 'void
>> llvm::SmallBitVector::applyMask<true,false>(const uint32_t *,unsigned
>> int)' being compiled (compiling source file
>> E:\llvm\llvm\tools\clang\lib\StaticAnalyzer\Core\FunctionSummary.cpp)
>>
>> I am reverting the patch (and r247972) temporarily since this also
>> generates a lot of warnings (everywhere SmallBitVector.h ends up being
>> included from) in r247983.
>>
>> ~Aaron
>>
>> >      }
>> > +    if (InvertMask) M = ~M;
>> > +    if (AddBits) setSmallBits(getSmallBits() | M);
>> > +    else         setSmallBits(getSmallBits() & ~M);
>> >    }
>> >  };
>> >
>> >
>> > Modified: llvm/trunk/unittests/ADT/BitVectorTest.cpp
>> > URL:
>> > http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/ADT/BitVectorTest.cpp?rev=247972&r1=247971&r2=247972&view=diff
>> >
>> > ==============================================================================
>> > --- llvm/trunk/unittests/ADT/BitVectorTest.cpp (original)
>> > +++ llvm/trunk/unittests/ADT/BitVectorTest.cpp Fri Sep 18 01:35:12 2015
>> > @@ -235,12 +235,12 @@ TYPED_TEST(BitVectorTest, PortableBitMas
>> >    const uint32_t Mask1[] = { 0x80000000, 6, 5 };
>> >
>> >    A.resize(10);
>> > -  A.setBitsInMask(Mask1, 3);
>> > +  A.setBitsInMask(Mask1, 2);
>> >    EXPECT_EQ(10u, A.size());
>> >    EXPECT_FALSE(A.test(0));
>> >
>> >    A.resize(32);
>> > -  A.setBitsInMask(Mask1, 3);
>> > +  A.setBitsInMask(Mask1, 2);
>> >    EXPECT_FALSE(A.test(0));
>> >    EXPECT_TRUE(A.test(31));
>> >    EXPECT_EQ(1u, A.count());
>> >
>> >
>> > _______________________________________________
>> > llvm-commits mailing list
>> > llvm-commits at lists.llvm.org
>> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits
>
>