From cbeb687c687e6edebd3afdb63be0a623294e744c Mon Sep 17 00:00:00 2001 From: Neal Norwitz Date: Sat, 14 Oct 2006 21:33:38 +0000 Subject: Update the peephole optimizer to remove more dead code (jumps after returns) and inline jumps to returns. --- Lib/test/test_peepholer.py | 35 +++++++++++++++++++++++++++++++++++ Misc/NEWS | 3 +++ Python/import.c | 3 ++- Python/peephole.c | 19 +++++++++++++++---- 4 files changed, 55 insertions(+), 5 deletions(-) diff --git a/Lib/test/test_peepholer.py b/Lib/test/test_peepholer.py index 4385a84..02b04e0 100644 --- a/Lib/test/test_peepholer.py +++ b/Lib/test/test_peepholer.py @@ -161,6 +161,41 @@ class TestTranforms(unittest.TestCase): self.assert_('(None)' not in asm) self.assertEqual(asm.split().count('RETURN_VALUE'), 1) + def test_elim_jump_to_return(self): + # JUMP_FORWARD to RETURN --> RETURN + def f(cond, true_value, false_value): + return true_value if cond else false_value + asm = disassemble(f) + self.assert_('JUMP_FORWARD' not in asm) + self.assert_('JUMP_ABSOLUTE' not in asm) + self.assertEqual(asm.split().count('RETURN_VALUE'), 2) + + def test_elim_jump_after_return1(self): + # Eliminate dead code: jumps immediately after returns can't be reached + def f(cond1, cond2): + if cond1: return 1 + if cond2: return 2 + while 1: + return 3 + while 1: + if cond1: return 4 + return 5 + return 6 + asm = disassemble(f) + self.assert_('JUMP_FORWARD' not in asm) + self.assert_('JUMP_ABSOLUTE' not in asm) + self.assertEqual(asm.split().count('RETURN_VALUE'), 6) + + def test_elim_jump_after_return2(self): + # Eliminate dead code: jumps immediately after returns can't be reached + def f(cond1, cond2): + while 1: + if cond1: return 4 + asm = disassemble(f) + self.assert_('JUMP_FORWARD' not in asm) + # There should be one jump for the while loop. + self.assertEqual(asm.split().count('JUMP_ABSOLUTE'), 1) + self.assertEqual(asm.split().count('RETURN_VALUE'), 2) def test_main(verbose=None): diff --git a/Misc/NEWS b/Misc/NEWS index cd21eea..9800a9b 100644 --- a/Misc/NEWS +++ b/Misc/NEWS @@ -12,6 +12,9 @@ What's New in Python 2.6 alpha 1? Core and builtins ----------------- +- Update the peephole optimizer to remove more dead code (jumps after returns) + and inline unconditional jumps to returns. + - Bug #1545497: when given an explicit base, int() did ignore NULs embedded in the string to convert. diff --git a/Python/import.c b/Python/import.c index a90729a..45c5507 100644 --- a/Python/import.c +++ b/Python/import.c @@ -65,9 +65,10 @@ extern time_t PyOS_GetLastModificationTime(char *, FILE *); Python 2.5c1: 62121 (fix wrong lnotab with for loops and storing constants that should have been removed) Python 2.5c2: 62131 (fix wrong code: for x, in ... in listcomp/genexp) + Python 2.6a0: 62141 (peephole optimizations) . */ -#define MAGIC (62131 | ((long)'\r'<<16) | ((long)'\n'<<24)) +#define MAGIC (62141 | ((long)'\r'<<16) | ((long)'\n'<<24)) /* Magic word as global; note that _PyImport_Init() can change the value of this global to accommodate for alterations of how the diff --git a/Python/peephole.c b/Python/peephole.c index 1d94319..f2fe6ce 100644 --- a/Python/peephole.c +++ b/Python/peephole.c @@ -523,6 +523,13 @@ PyCode_Optimize(PyObject *code, PyObject* consts, PyObject *names, case SETUP_EXCEPT: case SETUP_FINALLY: tgt = GETJUMPTGT(codestr, i); + /* Replace JUMP_* to a RETURN into just a RETURN */ + if (UNCONDITIONAL_JUMP(opcode) && + codestr[tgt] == RETURN_VALUE) { + codestr[i] = RETURN_VALUE; + memset(codestr+i+1, NOP, 2); + continue; + } if (!UNCONDITIONAL_JUMP(codestr[tgt])) continue; tgttgt = GETJUMPTGT(codestr, tgt); @@ -540,12 +547,16 @@ PyCode_Optimize(PyObject *code, PyObject* consts, PyObject *names, goto exitUnchanged; /* Replace RETURN LOAD_CONST None RETURN with just RETURN */ + /* Remove unreachable JUMPs after RETURN */ case RETURN_VALUE: - if (i+4 >= codelen || - codestr[i+4] != RETURN_VALUE || - !ISBASICBLOCK(blocks,i,5)) + if (i+4 >= codelen) continue; - memset(codestr+i+1, NOP, 4); + if (codestr[i+4] == RETURN_VALUE && + ISBASICBLOCK(blocks,i,5)) + memset(codestr+i+1, NOP, 4); + else if (UNCONDITIONAL_JUMP(codestr[i+1]) && + ISBASICBLOCK(blocks,i,4)) + memset(codestr+i+1, NOP, 3); break; } } -- cgit v0.12