<div dir="ltr">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.</div><div class="gmail_extra"><br clear="all"><div><div class="gmail_signature" data-smartmail="gmail_signature">~Craig</div></div>
<br><div class="gmail_quote">On Wed, Mar 1, 2017 at 2:42 PM, Ahmed Bougacha <span dir="ltr"><<a href="mailto:ahmed.bougacha@gmail.com" target="_blank">ahmed.bougacha@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">This seems really unfortunate.. It's very minor, but I found APInt<br>
very unexpected in this context. Could we fix SmallBitVector to<br>
actually be a "Small" template? Or honestly maybe just use<br>
SmallVector.<br>
<br>
-Ahmed<br>
<br>
<br>
On Mon, Feb 27, 2017 at 8:15 AM, Craig Topper via llvm-commits<br>
<<a href="mailto:llvm-commits@lists.llvm.org">llvm-commits@lists.llvm.org</a>> wrote:<br>
> Author: ctopper<br>
> Date: Mon Feb 27 10:15:25 2017<br>
> New Revision: 296352<br>
><br>
> URL: <a href="http://llvm.org/viewvc/llvm-project?rev=296352&view=rev" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-<wbr>project?rev=296352&view=rev</a><br>
> Log:<br>
> [X86] Use APInt instead of SmallBitVector for tracking undef elements in constant pool shuffle decoding<br>
><br>
> Summary:<br>
> 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.<br>
><br>
> 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.<br>
><br>
> Reviewers: RKSimon<br>
><br>
> Reviewed By: RKSimon<br>
><br>
> Subscribers: llvm-commits<br>
><br>
> Differential Revision: <a href="https://reviews.llvm.org/D30386" rel="noreferrer" target="_blank">https://reviews.llvm.org/<wbr>D30386</a><br>
><br>
> Modified:<br>
> llvm/trunk/lib/Target/X86/<wbr>X86ShuffleDecodeConstantPool.<wbr>cpp<br>
><br>
> Modified: llvm/trunk/lib/Target/X86/<wbr>X86ShuffleDecodeConstantPool.<wbr>cpp<br>
> URL: <a href="http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86ShuffleDecodeConstantPool.cpp?rev=296352&r1=296351&r2=296352&view=diff" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-<wbr>project/llvm/trunk/lib/Target/<wbr>X86/<wbr>X86ShuffleDecodeConstantPool.<wbr>cpp?rev=296352&r1=296351&r2=<wbr>296352&view=diff</a><br>
> ==============================<wbr>==============================<wbr>==================<br>
> --- llvm/trunk/lib/Target/X86/<wbr>X86ShuffleDecodeConstantPool.<wbr>cpp (original)<br>
> +++ llvm/trunk/lib/Target/X86/<wbr>X86ShuffleDecodeConstantPool.<wbr>cpp Mon Feb 27 10:15:25 2017<br>
> @@ -14,7 +14,7 @@<br>
><br>
> #include "X86ShuffleDecodeConstantPool.<wbr>h"<br>
> #include "Utils/X86ShuffleDecode.h"<br>
> -#include "llvm/ADT/SmallBitVector.h"<br>
> +#include "llvm/ADT/APInt.h"<br>
> #include "llvm/CodeGen/<wbr>MachineValueType.h"<br>
> #include "llvm/IR/Constants.h"<br>
><br>
> @@ -25,7 +25,7 @@<br>
> namespace llvm {<br>
><br>
> static bool extractConstantMask(const Constant *C, unsigned MaskEltSizeInBits,<br>
> - SmallBitVector &UndefElts,<br>
> + APInt &UndefElts,<br>
> SmallVectorImpl<uint64_t> &RawMask) {<br>
> // It is not an error for shuffle masks to not be a vector of<br>
> // MaskEltSizeInBits because the constant pool uniques constants by their<br>
> @@ -73,7 +73,7 @@ static bool extractConstantMask(const Co<br>
> "Unaligned shuffle mask size");<br>
><br>
> unsigned NumMaskElts = CstSizeInBits / MaskEltSizeInBits;<br>
> - UndefElts = SmallBitVector(NumMaskElts, false);<br>
> + UndefElts = APInt(NumMaskElts, 0);<br>
> RawMask.resize(NumMaskElts, 0);<br>
><br>
> for (unsigned i = 0; i != NumMaskElts; ++i) {<br>
> @@ -83,7 +83,7 @@ static bool extractConstantMask(const Co<br>
> // Only treat the element as UNDEF if all bits are UNDEF, otherwise<br>
> // treat it as zero.<br>
> if (EltUndef.isAllOnesValue()) {<br>
> - UndefElts[i] = true;<br>
> + UndefElts.setBit(i);<br>
> RawMask[i] = 0;<br>
> continue;<br>
> }<br>
> @@ -103,7 +103,7 @@ void DecodePSHUFBMask(const Constant *C,<br>
> "Unexpected vector size.");<br>
><br>
> // The shuffle mask requires a byte vector.<br>
> - SmallBitVector UndefElts;<br>
> + APInt UndefElts;<br>
> SmallVector<uint64_t, 32> RawMask;<br>
> if (!extractConstantMask(C, 8, UndefElts, RawMask))<br>
> return;<br>
> @@ -144,7 +144,7 @@ void DecodeVPERMILPMask(const Constant *<br>
> assert((ElSize == 32 || ElSize == 64) && "Unexpected vector element size.");<br>
><br>
> // The shuffle mask requires elements the same size as the target.<br>
> - SmallBitVector UndefElts;<br>
> + APInt UndefElts;<br>
> SmallVector<uint64_t, 8> RawMask;<br>
> if (!extractConstantMask(C, ElSize, UndefElts, RawMask))<br>
> return;<br>
> @@ -179,7 +179,7 @@ void DecodeVPERMIL2PMask(const Constant<br>
> assert((MaskTySize == 128 || MaskTySize == 256) && "Unexpected vector size.");<br>
><br>
> // The shuffle mask requires elements the same size as the target.<br>
> - SmallBitVector UndefElts;<br>
> + APInt UndefElts;<br>
> SmallVector<uint64_t, 8> RawMask;<br>
> if (!extractConstantMask(C, ElSize, UndefElts, RawMask))<br>
> return;<br>
> @@ -230,7 +230,7 @@ void DecodeVPPERMMask(const Constant *C,<br>
> "Unexpected vector size.");<br>
><br>
> // The shuffle mask requires a byte vector.<br>
> - SmallBitVector UndefElts;<br>
> + APInt UndefElts;<br>
> SmallVector<uint64_t, 32> RawMask;<br>
> if (!extractConstantMask(C, 8, UndefElts, RawMask))<br>
> return;<br>
> @@ -285,7 +285,7 @@ void DecodeVPERMVMask(const Constant *C,<br>
> "Unexpected vector element size.");<br>
><br>
> // The shuffle mask requires elements the same size as the target.<br>
> - SmallBitVector UndefElts;<br>
> + APInt UndefElts;<br>
> SmallVector<uint64_t, 8> RawMask;<br>
> if (!extractConstantMask(C, ElSize, UndefElts, RawMask))<br>
> return;<br>
> @@ -313,7 +313,7 @@ void DecodeVPERMV3Mask(const Constant *C<br>
> "Unexpected vector element size.");<br>
><br>
> // The shuffle mask requires elements the same size as the target.<br>
> - SmallBitVector UndefElts;<br>
> + APInt UndefElts;<br>
> SmallVector<uint64_t, 8> RawMask;<br>
> if (!extractConstantMask(C, ElSize, UndefElts, RawMask))<br>
> return;<br>
><br>
><br>
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</blockquote></div><br></div>