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C-Breeze C Compiler Infrastructure [ Project home page] |
dead.cc
Go to the documentation of this file.00001 // $Id: dead.cc,v 1.5 2003/08/07 23:14:12 pnav Exp $ 00002 // ---------------------------------------------------------------------- 00003 // 00004 // C-Breeze 00005 // C Compiler Framework 00006 // 00007 // Copyright (c) 2000 University of Texas at Austin 00008 // 00009 // Lipphei Adam 00010 // Samuel Z. Guyer 00011 // Daniel A. Jimenez 00012 // Calvin Lin 00013 // 00014 // Permission is hereby granted, free of charge, to any person 00015 // obtaining a copy of this software and associated documentation 00016 // files (the "Software"), to deal in the Software without 00017 // restriction, including without limitation the rights to use, copy, 00018 // modify, merge, publish, distribute, sublicense, and/or sell copies 00019 // of the Software, and to permit persons to whom the Software is 00020 // furnished to do so, subject to the following conditions: 00021 // 00022 // The above copyright notice and this permission notice shall be 00023 // included in all copies or substantial portions of the Software. 00024 // 00025 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, 00026 // EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF 00027 // MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND 00028 // NONINFRINGEMENT. IN NO EVENT SHALL THE UNIVERSITY OF TEXAS AT 00029 // AUSTIN BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER 00030 // IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF 00031 // OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN 00032 // THE SOFTWARE. 00033 // 00034 // We acknowledge the C-to-C Translator from MIT Laboratory for 00035 // Computer Science for inspiring parts of the C-Breeze design. 00036 // 00037 // ---------------------------------------------------------------------- 00038 // 00039 // dead.cc 00040 // 00041 // Dead code elimination 00042 // 00043 00044 #include "c_breeze.h" 00045 #include "live.h" 00046 #include "dead.h" 00047 00048 typedef stmt_list::reverse_iterator stmt_list_rp; 00049 00050 deadCodeEliminationChanger::deadCodeEliminationChanger () : 00051 Changer(Both, Subtree, false), _lw(NULL) 00052 {} 00053 00054 Node * deadCodeEliminationChanger::at_proc (procNode * proc, Order ord) { 00055 if (ord == Preorder) { 00056 // first perform the liveness analysis on the procedure 00057 // to get def, use, live_in and live_out information 00058 _lw = LivenessWalker::walk(proc); 00059 } 00060 else { // ord == Postorder 00061 UnusedDeclarationCleanupChanger udc; 00062 proc->change(udc); // remove any unused declarations 00063 00064 if (_lw) delete _lw; 00065 } 00066 return proc; 00067 } 00068 00069 Node * deadCodeEliminationChanger::at_threeAddr (threeAddrNode * node, Order ord) { 00070 if (ord == Postorder) { 00071 if (node->lhs()) { // this is an assignment statement 00072 id_list& ids = node->lhs()->fields(); 00073 // Assumption: non-empty fields = struct, non-empty index = array 00074 if ( (! ids.empty()) || node->lhs()->index() ) { 00075 return node; // skip any dead-code elimination 00076 } 00077 00078 // get the live_out for this stmt 00079 decl_set * live_out = _lw->live_out(node); 00080 // get the defs for this stmt 00081 decl_set * defs = _lw->defs(node); 00082 00083 bool in_live_out = false; 00084 for (decl_set_p iter = defs->begin() ; iter != defs->end() ; iter++) { 00085 declNode * decl = (* iter); 00086 // if this definition is in the live_out set, 00087 if (live_out->find(decl) != live_out->end()) { 00088 in_live_out = true; 00089 break; 00090 } 00091 } 00092 00093 // if this definition is NOT in the live_out set, 00094 // then it is a dead code 00095 if (! in_live_out) { 00096 // cout << "Deleting var " << decl->name() << endl; 00097 return NULL; 00098 } 00099 // else cout << "Var " << decl->name() << " is not deleted." << endl; 00100 } 00101 } 00102 return node; 00103 }