lib/Target/X86/AsmPrinter/X86InstComments.cpp

//===-- X86InstComments.cpp - Generate verbose-asm comments for instrs ----===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This defines functionality used to emit comments about X86 instructions to
// an output stream for -fverbose-asm.
//
//===----------------------------------------------------------------------===//

#include "X86InstComments.h"
#include "X86GenInstrNames.inc"
#include "llvm/MC/MCInst.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;

//===----------------------------------------------------------------------===//
//  Vector Mask Decoding
//===----------------------------------------------------------------------===//

enum {
  SM_SentinelZero = ~0U
};

static void DecodeINSERTPSMask(unsigned Imm, 
                               SmallVectorImpl<unsigned> &ShuffleMask) {
  // Defaults the copying the dest value.
  ShuffleMask.push_back(0);
  ShuffleMask.push_back(1);
  ShuffleMask.push_back(2);
  ShuffleMask.push_back(3);
  
  // Decode the immediate.
  unsigned ZMask = Imm & 15;
  unsigned CountD = (Imm >> 4) & 3;
  unsigned CountS = (Imm >> 6) & 3;
  
  // CountS selects which input element to use.
  unsigned InVal = 4+CountS;
  // CountD specifies which element of destination to update.
  ShuffleMask[CountD] = InVal;
  // ZMask zaps values, potentially overriding the CountD elt.
  if (ZMask & 1) ShuffleMask[0] = SM_SentinelZero;
  if (ZMask & 2) ShuffleMask[1] = SM_SentinelZero;
  if (ZMask & 4) ShuffleMask[2] = SM_SentinelZero;
  if (ZMask & 8) ShuffleMask[3] = SM_SentinelZero;
}

static void DecodeSHUFPSMask(unsigned NElts, unsigned Imm,
                             SmallVectorImpl<unsigned> &ShuffleMask) {
  // Part that reads from dest.
  for (unsigned i = 0; i != NElts/2; ++i) {
    ShuffleMask.push_back(Imm % NElts);
    Imm /= NElts;
  }
  // Part that reads from src.
  for (unsigned i = 0; i != NElts/2; ++i) {
    ShuffleMask.push_back(Imm % NElts + NElts);
    Imm /= NElts;
  }
}

static void DecodePSHUFMask(unsigned NElts, unsigned Imm,
                            SmallVectorImpl<unsigned> &ShuffleMask) {
  for (unsigned i = 0; i != NElts; ++i) {
    ShuffleMask.push_back(Imm % NElts);
    Imm /= NElts;
  }
}

/// DecodeUNPCKLPMask - This decodes the shuffle masks for unpcklps/unpcklpd
/// etc.  NElts indicates the number of elements in the vector allowing it to
/// handle different datatypes and vector widths.
static void DecodeUNPCKLPMask(unsigned NElts,
                              SmallVectorImpl<unsigned> &ShuffleMask) {
  for (unsigned i = 0; i != NElts/2; ++i) {
    ShuffleMask.push_back(i);        // Reads from dest
    ShuffleMask.push_back(i+NElts);  // Reads from src
  }
}

//===----------------------------------------------------------------------===//
// Top Level Entrypoint
//===----------------------------------------------------------------------===//


/// EmitAnyX86InstComments - This function decodes x86 instructions and prints
/// newline terminated strings to the specified string if desired.  This
/// information is shown in disassembly dumps when verbose assembly is enabled.
void llvm::EmitAnyX86InstComments(const MCInst *MI, raw_ostream &OS,
                                  const char *(*getRegName)(unsigned)) {
  // If this is a shuffle operation, the switch should fill in this state.
  SmallVector<unsigned, 8> ShuffleMask;
  const char *DestName = 0, *Src1Name = 0, *Src2Name = 0;
  
  switch (MI->getOpcode()) {
  case X86::INSERTPSrr:
    Src1Name = getRegName(MI->getOperand(1).getReg());
    Src2Name = getRegName(MI->getOperand(2).getReg());
    DecodeINSERTPSMask(MI->getOperand(3).getImm(), ShuffleMask);
    break;
  case X86::PSHUFDri:
    Src1Name = getRegName(MI->getOperand(1).getReg());
    // FALL THROUGH.
  case X86::PSHUFDmi:
    DestName = getRegName(MI->getOperand(0).getReg());
    DecodePSHUFMask(4, MI->getOperand(MI->getNumOperands()-1).getImm(),
                    ShuffleMask);
    break;

  case X86::SHUFPDrri:
    DecodeSHUFPSMask(2, MI->getOperand(3).getImm(), ShuffleMask);
    Src1Name = getRegName(MI->getOperand(0).getReg());
    Src2Name = getRegName(MI->getOperand(2).getReg());
    break;
  case X86::SHUFPSrri:
    DecodeSHUFPSMask(4, MI->getOperand(3).getImm(), ShuffleMask);
    Src1Name = getRegName(MI->getOperand(0).getReg());
    Src2Name = getRegName(MI->getOperand(2).getReg());
    break;
  case X86::UNPCKLPSrr:
    Src2Name = getRegName(MI->getOperand(2).getReg());
    // FALL THROUGH.
  case X86::UNPCKLPSrm:
    DecodeUNPCKLPMask(4, ShuffleMask);
    Src1Name = getRegName(MI->getOperand(0).getReg());
    break;
  }

  
  // If this was a shuffle operation, print the shuffle mask.
  if (!ShuffleMask.empty()) {
    if (DestName == 0) DestName = Src1Name;
    OS << (DestName ? DestName : "mem") << " = ";
    
    // If the two sources are the same, canonicalize the input elements to be
    // from the first src so that we get larger element spans.
    if (Src1Name == Src2Name) {
      for (unsigned i = 0, e = ShuffleMask.size(); i != e; ++i) {
        if ((int)ShuffleMask[i] >= 0 && // Not sentinel.
            ShuffleMask[i] >= e)        // From second mask.
          ShuffleMask[i] -= e;
      }
    }
    
    // The shuffle mask specifies which elements of the src1/src2 fill in the
    // destination, with a few sentinel values.  Loop through and print them
    // out.
    for (unsigned i = 0, e = ShuffleMask.size(); i != e; ++i) {
      if (i != 0)
        OS << ',';
      if (ShuffleMask[i] == SM_SentinelZero) {
        OS << "zero";
        continue;
      }
      
      // Otherwise, it must come from src1 or src2.  Print the span of elements
      // that comes from this src.
      bool isSrc1 = ShuffleMask[i] < ShuffleMask.size();
      const char *SrcName = isSrc1 ? Src1Name : Src2Name;
      OS << (SrcName ? SrcName : "mem") << '[';
      bool IsFirst = true;
      while (i != e &&
             (int)ShuffleMask[i] >= 0 &&
             (ShuffleMask[i] < ShuffleMask.size()) == isSrc1) {
        if (!IsFirst)
          OS << ',';
        else
          IsFirst = false;
        OS << ShuffleMask[i] % ShuffleMask.size();
        ++i;
      }
      OS << ']';
      --i;  // For loop increments element #.
    }
    //MI->print(OS, 0);
    OS << "\n";
  }
  
}