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// $Id$ -*-c++-*-
//***************************************************************************
// File:
// InstrSelection.cpp
//
// Purpose:
// Machine-independent driver file for instruction selection.
// This file constructs a forest of BURG instruction trees and then
// uses the BURG-generated tree grammar (BURM) to find the optimal
// instruction sequences for a given machine.
//
// History:
// 7/02/01 - Vikram Adve - Created
//**************************************************************************/
#include "llvm/CodeGen/InstrSelection.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Instruction.h"
#include "llvm/BasicBlock.h"
#include "llvm/Method.h"
static bool SelectInstructionsForTree(InstrTreeNode* treeRoot, int goalnt,
TargetMachine &Target);
enum SelectDebugLevel_t {
Select_NoDebugInfo,
Select_PrintMachineCode,
Select_DebugInstTrees,
Select_DebugBurgTrees,
};
// Enable Debug Options to be specified on the command line
cl::Enum<enum SelectDebugLevel_t> SelectDebugLevel("dselect", cl::NoFlags,
"enable instruction selection debugging information",
clEnumValN(Select_NoDebugInfo, "n", "disable debug output"),
clEnumValN(Select_PrintMachineCode, "y", "print generated machine code"),
clEnumValN(Select_DebugInstTrees, "i", "print debugging info for instruction selection "),
clEnumValN(Select_DebugBurgTrees, "b", "print burg trees"), 0);
//---------------------------------------------------------------------------
// Entry point for instruction selection using BURG.
// Returns true if instruction selection failed, false otherwise.
//---------------------------------------------------------------------------
bool
SelectInstructionsForMethod(Method* method, TargetMachine &Target)
{
bool failed = false;
//
// Build the instruction trees to be given as inputs to BURG.
//
InstrForest instrForest(method);
if (SelectDebugLevel >= Select_DebugInstTrees)
{
cout << "\n\n*** Instruction trees for method "
<< (method->hasName()? method->getName() : "")
<< endl << endl;
instrForest.dump();
}
//
// Invoke BURG instruction selection for each tree
//
const hash_set<InstructionNode*> &treeRoots = instrForest.getRootSet();
for (hash_set<InstructionNode*>::const_iterator
treeRootIter = treeRoots.begin(); treeRootIter != treeRoots.end();
++treeRootIter)
{
InstrTreeNode* basicNode = *treeRootIter;
// Invoke BURM to label each tree node with a state
burm_label(basicNode);
if (SelectDebugLevel >= Select_DebugBurgTrees)
{
printcover(basicNode, 1, 0);
cerr << "\nCover cost == " << treecost(basicNode, 1, 0) << "\n\n";
printMatches(basicNode);
}
// Then recursively walk the tree to select instructions
if (SelectInstructionsForTree(basicNode, /*goalnt*/1, Target))
{
failed = true;
break;
}
}
//
// Record instructions in the vector for each basic block
//
for (Method::iterator BI = method->begin(); BI != method->end(); ++BI)
{
MachineCodeForBasicBlock& bbMvec = (*BI)->getMachineInstrVec();
for (BasicBlock::iterator II = (*BI)->begin(); II != (*BI)->end(); ++II)
{
MachineCodeForVMInstr& mvec = (*II)->getMachineInstrVec();
for (unsigned i=0; i < mvec.size(); i++)
bbMvec.push_back(mvec[i]);
}
}
if (SelectDebugLevel >= Select_PrintMachineCode)
{
cout << endl << "*** Machine instructions after INSTRUCTION SELECTION" << endl;
PrintMachineInstructions(method);
}
return false;
}
//*********************** Private Functions *****************************/
//---------------------------------------------------------------------------
// Function SelectInstructionsForTree
//
// Recursively walk the tree to select instructions.
// Do this top-down so that child instructions can exploit decisions
// made at the child instructions.
//
// E.g., if br(setle(reg,const)) decides the constant is 0 and uses
// a branch-on-integer-register instruction, then the setle node
// can use that information to avoid generating the SUBcc instruction.
//
// Note that this cannot be done bottom-up because setle must do this
// only if it is a child of the branch (otherwise, the result of setle
// may be used by multiple instructions).
//---------------------------------------------------------------------------
bool
SelectInstructionsForTree(InstrTreeNode* treeRoot, int goalnt,
TargetMachine &Target)
{
// Use a static vector to avoid allocating a new one per VM instruction
static MachineInstr* minstrVec[MAX_INSTR_PER_VMINSTR];
// Get the rule that matches this node.
//
int ruleForNode = burm_rule(treeRoot->state, goalnt);
if (ruleForNode == 0)
{
cerr << "Could not match instruction tree for instr selection" << endl;
assert(0);
return true;
}
// Get this rule's non-terminals and the corresponding child nodes (if any)
//
short *nts = burm_nts[ruleForNode];
// First, select instructions for the current node and rule.
// (If this is a list node, not an instruction, then skip this step).
// This function is specific to the target architecture.
//
if (treeRoot->opLabel != VRegListOp)
{
InstructionNode* instrNode = (InstructionNode*)treeRoot;
assert(instrNode->getNodeType() == InstrTreeNode::NTInstructionNode);
unsigned N = GetInstructionsByRule(instrNode, ruleForNode, nts, Target,
minstrVec);
assert(N <= MAX_INSTR_PER_VMINSTR);
for (unsigned i=0; i < N; i++)
{
assert(minstrVec[i] != NULL);
instrNode->getInstruction()->addMachineInstruction(minstrVec[i]);
}
}
// Then, recursively compile the child nodes, if any.
//
if (nts[0])
{ // i.e., there is at least one kid
InstrTreeNode* kids[2];
int currentRule = ruleForNode;
burm_kids(treeRoot, currentRule, kids);
// First skip over any chain rules so that we don't visit
// the current node again.
//
while (ThisIsAChainRule(currentRule))
{
currentRule = burm_rule(treeRoot->state, nts[0]);
nts = burm_nts[currentRule];
burm_kids(treeRoot, currentRule, kids);
}
// Now we have the first non-chain rule so we have found
// the actual child nodes. Recursively compile them.
//
for (int i = 0; nts[i]; i++)
{
assert(i < 2);
InstrTreeNode::InstrTreeNodeType nodeType = kids[i]->getNodeType();
if (nodeType == InstrTreeNode::NTVRegListNode ||
nodeType == InstrTreeNode::NTInstructionNode)
{
if (SelectInstructionsForTree(kids[i], nts[i], Target))
return true; // failure
}
}
}
return false; // success
}
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