[llvm-commits] CVS: llvm/lib/Bytecode/Writer/Writer.cpp

[Reid Spencer]

Christopher,

I'll answer my own question .. You're compressing the alignment to a
smaller value by extracting its log. I didn't get that until I read the
Reader.cpp code :)

Reid.

On Sat, 2007-04-21 at 09:46 -0700, Reid Spencer wrote:
> Christopher,
> 
> On Sat, 2007-04-21 at 03:17 -0500, Christopher Lamb wrote:
> > 
> > Changes in directory llvm/lib/Bytecode/Writer:
> > 
> > Writer.cpp updated: 1.173 -> 1.174
> > ---
> > Log message:
> > 
> > 
> > add support for alignment attributes on load/store instructions
> > 
> > 
> > ---
> > Diffs of the changes:  (+27 -5)
> > 
> >  Writer.cpp |   32 +++++++++++++++++++++++++++-----
> >  1 files changed, 27 insertions(+), 5 deletions(-)
> > 
> > 
> > Index: llvm/lib/Bytecode/Writer/Writer.cpp
> > diff -u llvm/lib/Bytecode/Writer/Writer.cpp:1.173 llvm/lib/Bytecode/Writer/Writer.cpp:1.174
> > --- llvm/lib/Bytecode/Writer/Writer.cpp:1.173	Mon Apr 16 18:32:28 2007
> > +++ llvm/lib/Bytecode/Writer/Writer.cpp	Sat Apr 21 03:16:25 2007
> > @@ -616,7 +616,7 @@
> >    unsigned Opcode = I.getOpcode();
> >    unsigned NumOperands = I.getNumOperands();
> >  
> > -  // Encode 'tail call' as 61, 'volatile load' as 62, and 'volatile store' as
> > +  // Encode 'tail call' as 61
> >    // 63.
> >    if (const CallInst *CI = dyn_cast<CallInst>(&I)) {
> >      if (CI->getCallingConv() == CallingConv::C) {
> > @@ -632,10 +632,6 @@
> >      } else {
> >        Opcode = 58;      // Call escape sequence.
> >      }
> > -  } else if (isa<LoadInst>(I) && cast<LoadInst>(I).isVolatile()) {
> > -    Opcode = 62;
> > -  } else if (isa<StoreInst>(I) && cast<StoreInst>(I).isVolatile()) {
> > -    Opcode = 63;
> >    }
> >  
> >    // Figure out which type to encode with the instruction.  Typically we want
> > @@ -744,6 +740,32 @@
> >      } else if (isa<InvokeInst>(I)) {
> >        // Invoke escape seq has at least 4 operands to encode.
> >        ++NumOperands;
> > +    } else if (const LoadInst *LI = dyn_cast<LoadInst>(&I)) {
> > +      // Encode attributed load as opcode 62
> > +      // We need to encode the attributes of the load instruction as the second
> > +      // operand. Its not really a slot, but we don't want to break the 
> > +      // instruction format for these instructions.
> > +      if (LI->getAlignment() || LI->isVolatile()) {
> > +        NumOperands = 2;
> > +        Slots[1] = ((Log2_32(LI->getAlignment())+1)<<1) + 
> > +                    (LI->isVolatile() ? 1 : 0);
> 
> Is this Log2_32 really needed? The alignment should already be a power
> of two.  If the alignment is something like 7 then you'll get rounding
> to 8 but I contend that an alignment of 7 can't happen. This can be
> assured in the bcreader and the asmparser.
> 
> > +        if (Slots[1] > MaxOpSlot) 
> > +          MaxOpSlot = Slots[1];
> > +        Opcode = 62;
> > +      }
> > +    } else if (const StoreInst *SI = dyn_cast<StoreInst>(&I)) {
> > +      // Encode attributed store as opcode 63
> > +      // We need to encode the attributes of the store instruction as the third
> > +      // operand. Its not really a slot, but we don't want to break the 
> > +      // instruction format for these instructions.
> > +      if (SI->getAlignment() || SI->isVolatile()) {
> > +        NumOperands = 3;
> > +        Slots[2] = ((Log2_32(SI->getAlignment())+1)<<1) + 
> > +                    (SI->isVolatile() ? 1 : 0);
> > +        if (Slots[2] > MaxOpSlot) 
> > +          MaxOpSlot = Slots[2];
> > +        Opcode = 63;
> > +      }
> >      }
> >  
> >      // Decide which instruction encoding to use.  This is determined primarily
> > 
> > 
> > 
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