path: root/lib/CodeGen/IfConversion.cpp

//===-- IfConversion.cpp - Machine code if conversion pass. ---------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file was developed by the Evan Cheng and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the machine instruction level if-conversion pass.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "ifcvt"
#include "llvm/Function.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/CodeGen/MachineModuleInfo.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/Target/TargetInstrInfo.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/Statistic.h"
using namespace llvm;

namespace {
  // Hidden options for help debugging.
  cl::opt<int> IfCvtFnStart("ifcvt-fn-start", cl::init(-1), cl::Hidden);
  cl::opt<int> IfCvtFnStop("ifcvt-fn-stop", cl::init(-1), cl::Hidden);
  cl::opt<int> IfCvtLimit("ifcvt-limit", cl::init(-1), cl::Hidden);
  cl::opt<bool> DisableSimple("disable-ifcvt-simple", 
                              cl::init(false), cl::Hidden);
  cl::opt<bool> DisableSimpleF("disable-ifcvt-simple-false", 
                               cl::init(false), cl::Hidden);
  cl::opt<bool> DisableTriangle("disable-ifcvt-triangle", 
                                cl::init(false), cl::Hidden);
  cl::opt<bool> DisableTriangleR("disable-ifcvt-triangle-rev", 
                                 cl::init(false), cl::Hidden);
  cl::opt<bool> DisableTriangleF("disable-ifcvt-triangle-false", 
                                 cl::init(false), cl::Hidden);
  cl::opt<bool> DisableTriangleFR("disable-ifcvt-triangle-false-rev", 
                                  cl::init(false), cl::Hidden);
  cl::opt<bool> DisableDiamond("disable-ifcvt-diamond", 
                               cl::init(false), cl::Hidden);
}

STATISTIC(NumSimple,       "Number of simple if-conversions performed");
STATISTIC(NumSimpleFalse,  "Number of simple (F) if-conversions performed");
STATISTIC(NumTriangle,     "Number of triangle if-conversions performed");
STATISTIC(NumTriangleRev,  "Number of triangle (R) if-conversions performed");
STATISTIC(NumTriangleFalse,"Number of triangle (F) if-conversions performed");
STATISTIC(NumTriangleFRev, "Number of triangle (F/R) if-conversions performed");
STATISTIC(NumDiamonds,     "Number of diamond if-conversions performed");
STATISTIC(NumIfConvBBs,    "Number of if-converted blocks");
STATISTIC(NumDupBBs,       "Number of duplicated blocks");

namespace {
  class IfConverter : public MachineFunctionPass {
    enum BBICKind {
      ICNotClassfied,  // BB data valid, but not classified.
      ICSimple,        // BB is entry of an one split, no rejoin sub-CFG.
      ICSimpleFalse,   // Same as ICSimple, but on the false path.
      ICTriangle,      // BB is entry of a triangle sub-CFG.
      ICTriangleRev,   // Same as ICTriangle, but true path rev condition.
      ICTriangleFalse, // Same as ICTriangle, but on the false path.
      ICTriangleFRev,  // Same as ICTriangleFalse, but false path rev condition.
      ICDiamond        // BB is entry of a diamond sub-CFG.
    };

    /// BBInfo - One per MachineBasicBlock, this is used to cache the result
    /// if-conversion feasibility analysis. This includes results from
    /// TargetInstrInfo::AnalyzeBranch() (i.e. TBB, FBB, and Cond), and its
    /// classification, and common tail block of its successors (if it's a
    /// diamond shape), its size, whether it's predicable, and whether any
    /// instruction can clobber the 'would-be' predicate.
    ///
    /// Kind            - Type of block. See BBICKind.
    /// IsDone          - True if BB is not to be considered for ifcvt.
    /// IsBeingAnalyzed - True if BB is currently being analyzed.
    /// IsAnalyzed      - True if BB has been analyzed (info is still valid).
    /// IsEnqueued      - True if BB has been enqueued to be ifcvt'ed.
    /// IsBrAnalyzable  - True if AnalyzeBranch() returns false.
    /// HasFallThrough  - True if BB may fallthrough to the following BB.
    /// IsUnpredicable  - True if BB is known to be unpredicable.
    /// ClobbersPredicate- True if BB would modify the predicate (e.g. has
    ///                   cmp, call, etc.)
    /// NonPredSize     - Number of non-predicated instructions.
    /// BB              - Corresponding MachineBasicBlock.
    /// TrueBB / FalseBB- See AnalyzeBranch().
    /// BrCond          - Conditions for end of block conditional branches.
    /// Predicate       - Predicate used in the BB.
    struct BBInfo {
      BBICKind Kind;
      bool IsDone          : 1;
      bool IsBeingAnalyzed : 1;
      bool IsAnalyzed      : 1;
      bool IsEnqueued      : 1;
      bool IsBrAnalyzable  : 1;
      bool HasFallThrough  : 1;
      bool IsUnpredicable  :