[llvm] r296352 - [X86] Use APInt instead of SmallBitVector for tracking undef elements in constant pool shuffle decoding

[Craig Topper via llvm-commits]

This isn't as uncommon as you may think. SimplifyDemandedVectorElts in
InstCombine uses APInt like this too. We also use APInt for
knownzero/knownone for computeKnownBits in both InstCombine and DAGCombine.

~Craig

On Wed, Mar 1, 2017 at 2:42 PM, Ahmed Bougacha <ahmed.bougacha at gmail.com>
wrote:

> This seems really unfortunate..  It's very minor, but I found APInt
> very unexpected in this context.  Could we fix SmallBitVector to
> actually be a "Small" template?  Or honestly maybe just use
> SmallVector.
>
> -Ahmed
>
>
> On Mon, Feb 27, 2017 at 8:15 AM, Craig Topper via llvm-commits
> <llvm-commits at lists.llvm.org> wrote:
> > Author: ctopper
> > Date: Mon Feb 27 10:15:25 2017
> > New Revision: 296352
> >
> > URL: http://llvm.org/viewvc/llvm-project?rev=296352&view=rev
> > Log:
> > [X86] Use APInt instead of SmallBitVector for tracking undef elements in
> constant pool shuffle decoding
> >
> > Summary:
> > SmallBitVector uses a malloc for more than 58 bits on a 64-bit target
> and more than 27 bits on a 32-bit target. Some of the vector types we deal
> with here use more than those number of elements and therefore cause a
> malloc.
> >
> > APInt on the other hand supports up to 64 bits without a malloc. That's
> the maximum number of bits we need here so we can avoid a malloc for all
> cases by using APInt. This will incur a minor increase in stack usage due
> to APInt storing the bit count separately from the data bits unlike
> SmallBitVector, but that should be ok.
> >
> > Reviewers: RKSimon
> >
> > Reviewed By: RKSimon
> >
> > Subscribers: llvm-commits
> >
> > Differential Revision: https://reviews.llvm.org/D30386
> >
> > Modified:
> >     llvm/trunk/lib/Target/X86/X86ShuffleDecodeConstantPool.cpp
> >
> > Modified: llvm/trunk/lib/Target/X86/X86ShuffleDecodeConstantPool.cpp
> > URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/
> X86ShuffleDecodeConstantPool.cpp?rev=296352&r1=296351&r2=296352&view=diff
> > ============================================================
> ==================
> > --- llvm/trunk/lib/Target/X86/X86ShuffleDecodeConstantPool.cpp
> (original)
> > +++ llvm/trunk/lib/Target/X86/X86ShuffleDecodeConstantPool.cpp Mon Feb
> 27 10:15:25 2017
> > @@ -14,7 +14,7 @@
> >
> >  #include "X86ShuffleDecodeConstantPool.h"
> >  #include "Utils/X86ShuffleDecode.h"
> > -#include "llvm/ADT/SmallBitVector.h"
> > +#include "llvm/ADT/APInt.h"
> >  #include "llvm/CodeGen/MachineValueType.h"
> >  #include "llvm/IR/Constants.h"
> >
> > @@ -25,7 +25,7 @@
> >  namespace llvm {
> >
> >  static bool extractConstantMask(const Constant *C, unsigned
> MaskEltSizeInBits,
> > -                                SmallBitVector &UndefElts,
> > +                                APInt &UndefElts,
> >                                  SmallVectorImpl<uint64_t> &RawMask) {
> >    // It is not an error for shuffle masks to not be a vector of
> >    // MaskEltSizeInBits because the constant pool uniques constants by
> their
> > @@ -73,7 +73,7 @@ static bool extractConstantMask(const Co
> >           "Unaligned shuffle mask size");
> >
> >    unsigned NumMaskElts = CstSizeInBits / MaskEltSizeInBits;
> > -  UndefElts = SmallBitVector(NumMaskElts, false);
> > +  UndefElts = APInt(NumMaskElts, 0);
> >    RawMask.resize(NumMaskElts, 0);
> >
> >    for (unsigned i = 0; i != NumMaskElts; ++i) {
> > @@ -83,7 +83,7 @@ static bool extractConstantMask(const Co
> >      // Only treat the element as UNDEF if all bits are UNDEF, otherwise
> >      // treat it as zero.
> >      if (EltUndef.isAllOnesValue()) {
> > -      UndefElts[i] = true;
> > +      UndefElts.setBit(i);
> >        RawMask[i] = 0;
> >        continue;
> >      }
> > @@ -103,7 +103,7 @@ void DecodePSHUFBMask(const Constant *C,
> >           "Unexpected vector size.");
> >
> >    // The shuffle mask requires a byte vector.
> > -  SmallBitVector UndefElts;
> > +  APInt UndefElts;
> >    SmallVector<uint64_t, 32> RawMask;
> >    if (!extractConstantMask(C, 8, UndefElts, RawMask))
> >      return;
> > @@ -144,7 +144,7 @@ void DecodeVPERMILPMask(const Constant *
> >    assert((ElSize == 32 || ElSize == 64) && "Unexpected vector element
> size.");
> >
> >    // The shuffle mask requires elements the same size as the target.
> > -  SmallBitVector UndefElts;
> > +  APInt UndefElts;
> >    SmallVector<uint64_t, 8> RawMask;
> >    if (!extractConstantMask(C, ElSize, UndefElts, RawMask))
> >      return;
> > @@ -179,7 +179,7 @@ void DecodeVPERMIL2PMask(const Constant
> >    assert((MaskTySize == 128 || MaskTySize == 256) && "Unexpected vector
> size.");
> >
> >    // The shuffle mask requires elements the same size as the target.
> > -  SmallBitVector UndefElts;
> > +  APInt UndefElts;
> >    SmallVector<uint64_t, 8> RawMask;
> >    if (!extractConstantMask(C, ElSize, UndefElts, RawMask))
> >      return;
> > @@ -230,7 +230,7 @@ void DecodeVPPERMMask(const Constant *C,
> >           "Unexpected vector size.");
> >
> >    // The shuffle mask requires a byte vector.
> > -  SmallBitVector UndefElts;
> > +  APInt UndefElts;
> >    SmallVector<uint64_t, 32> RawMask;
> >    if (!extractConstantMask(C, 8, UndefElts, RawMask))
> >      return;
> > @@ -285,7 +285,7 @@ void DecodeVPERMVMask(const Constant *C,
> >           "Unexpected vector element size.");
> >
> >    // The shuffle mask requires elements the same size as the target.
> > -  SmallBitVector UndefElts;
> > +  APInt UndefElts;
> >    SmallVector<uint64_t, 8> RawMask;
> >    if (!extractConstantMask(C, ElSize, UndefElts, RawMask))
> >      return;
> > @@ -313,7 +313,7 @@ void DecodeVPERMV3Mask(const Constant *C
> >           "Unexpected vector element size.");
> >
> >    // The shuffle mask requires elements the same size as the target.
> > -  SmallBitVector UndefElts;
> > +  APInt UndefElts;
> >    SmallVector<uint64_t, 8> RawMask;
> >    if (!extractConstantMask(C, ElSize, UndefElts, RawMask))
> >      return;
> >
> >
> > _______________________________________________
> > llvm-commits mailing list
> > llvm-commits at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20170301/b68b39b9/attachment.html>