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Get rid of DoesSomething() in favour of SEF

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The missing bit was to mark labels are SEF when they are not referenced. Label references are now counted at parse time, enabling us to do this.

Also, make FoldStmt clearer when the node is an expression.
This commit is contained in:
Sei Lisa 2018-05-17 08:12:33 +02:00
parent a93ea0ca19
commit 285c7172fd
3 changed files with 71 additions and 55 deletions
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6
lslopt/lsldeadcode.py
View file

@ -384,6 +384,12 @@ class deadcode(object):
node = curnode.ch[index] node = curnode.ch[index]
if not hasattr(node, 'X'): if not hasattr(node, 'X'):
if curnode.ch[index].nt == 'JUMP':
# Decrease label reference count
scope = curnode.ch[index].scope
name = curnode.ch[index].name
assert self.symtab[scope][name]['ref'] > 0
self.symtab[scope][name]['ref'] -= 1
del curnode.ch[index] del curnode.ch[index]
continue continue

43
lslopt/lslfoldconst.py
View file

@ -107,25 +107,6 @@ class foldconst(object):
else: else:
idx += 1 idx += 1
def DoesSomething(self, node, labels = False):
"""Tell if a subtree does something or is just empty statements
(a pure combination of ';' and '{}'). Labels are the top level are
considered to do something if labels is True, and vice versa.
Not to be confused with lslparse.does_something which always includes
labels, and applies to a block's statement list, not to a node.
"""
maybe_label = ';' if labels else '@'
if maybe_label != node.nt != ';' and not node.SEF:
if node.nt == '{}':
for subnode in node.ch:
# Labels embedded in {} are not reachable. They do nothing.
if self.DoesSomething(subnode):
return True
else:
return True
return False
def CompareTrees(self, node1, node2): def CompareTrees(self, node1, node2):
"""Try to compare two subtrees to see if they are equivalent.""" """Try to compare two subtrees to see if they are equivalent."""
# They MUST be SEF and stable. # They MUST be SEF and stable.
@ -186,8 +167,6 @@ class foldconst(object):
def FoldStmt(self, parent, index): def FoldStmt(self, parent, index):
"""Simplify a statement.""" """Simplify a statement."""
node = parent[index] node = parent[index]
if node.nt == 'EXPR':
node = node.ch[0]
# If the statement is side-effect-free, remove it as it does nothing. # If the statement is side-effect-free, remove it as it does nothing.
if node.SEF: if node.SEF:
# When a statement is side-effect free, it does nothing except # When a statement is side-effect free, it does nothing except
@ -205,6 +184,8 @@ class foldconst(object):
# Other unary and binary operators are side effect-free. # Other unary and binary operators are side effect-free.
parent[index] = nr(nt=';', t=None, SEF=True) parent[index] = nr(nt=';', t=None, SEF=True)
return return
if node.nt == 'EXPR':
node = node.ch[0]
# Post-increments take more space than pre-increments. # Post-increments take more space than pre-increments.
if node.nt in ('V++', 'V--'): if node.nt in ('V++', 'V--'):
node.nt = '++V' if node.nt == 'V++' else '--V'; node.nt = '++V' if node.nt == 'V++' else '--V';
@ -1525,14 +1506,15 @@ class foldconst(object):
self.CurEvent = node.name self.CurEvent = node.name
self.FoldTree(child, 0) self.FoldTree(child, 0)
# Test if the event is empty and SEF, and remove it if so. # Test if the event is SEF and does nothing, and remove it if so.
if (not hasattr(node, 'scope') and not self.DoesSomething(child[0]) if (not hasattr(node, 'scope') and child[0].SEF
and 'SEF' in self.events[node.name] and 'SEF' in self.events[node.name]
): ):
# Delete ourselves. # Delete ourselves.
del parent[index] del parent[index]
return return
# Delete trailing bare RETURNs.
# TODO: This works, but analysis of code paths is DCR's thing # TODO: This works, but analysis of code paths is DCR's thing
# and this is incomplete, e.g. x(){{return;}} is not detected. # and this is incomplete, e.g. x(){{return;}} is not detected.
while child[0].ch: while child[0].ch:
@ -1621,7 +1603,7 @@ class foldconst(object):
self.FoldTree(child, 2) self.FoldTree(child, 2)
self.FoldStmt(child, 2) self.FoldStmt(child, 2)
# Check if it makes sense to swap if and else branches # Check if it makes sense to swap if and else branches
if (self.DoesSomething(child[2])): if not child[2].SEF:
# Check if we can gain something by negating the # Check if we can gain something by negating the
# expression. # expression.
# Swap 'if' and 'else' branch when the condition has # Swap 'if' and 'else' branch when the condition has
@ -1637,10 +1619,10 @@ class foldconst(object):
child[0].nt = '^' child[0].nt = '^'
child[1], child[2] = child[2], child[1] child[1], child[2] = child[2], child[1]
# Re-test just in case we swapped in the previous check. # Re-test just in case we swapped in the previous check.
if not self.DoesSomething(child[2]): if child[2].SEF:
# no point in "... else ;" - remove else branch # no point in "... else ;" - remove else branch
del child[2] del child[2]
if not self.DoesSomething(child[1]): if child[1].SEF:
# if (X) ; -> X; # if (X) ; -> X;
if len(child) == 2: if len(child) == 2:
parent[index] = nr(nt='EXPR', t=child[0].t, parent[index] = nr(nt='EXPR', t=child[0].t,
@ -1676,7 +1658,7 @@ class foldconst(object):
# out anyway. Otherwise we just don't know if it may be infinite, # out anyway. Otherwise we just don't know if it may be infinite,
# even if every component is SEF. # even if every component is SEF.
if self.DoesSomething(child[1]): if not child[1].SEF:
self.ExpandCondition(child, 0) self.ExpandCondition(child, 0)
self.FoldTree(child, 0) self.FoldTree(child, 0)
@ -1822,7 +1804,12 @@ class foldconst(object):
node.SEF = True node.SEF = True
return return
if nt in ('JUMP', '@', 'V++', 'V--', '--V', '++V', 'LAMBDA'): if nt == '@':
# SEF if there are no JUMPs jumping to it
node.SEF = not self.symtab[node.scope][node.name]['ref']
return
if nt in ('JUMP', 'V++', 'V--', '--V', '++V', 'LAMBDA'):
# Except LAMBDA, these all have side effects, as in, can't be # Except LAMBDA, these all have side effects, as in, can't be
# eliminated as statements. # eliminated as statements.
# LAMBDA can't be eliminated without scrolling Loc's. # LAMBDA can't be eliminated without scrolling Loc's.

77
lslopt/lslparse.py
View file

@ -1712,12 +1712,13 @@ list lazy_list_set(list L, integer i, list v)
if name in self.locallabels or self.shrinknames: if name in self.locallabels or self.shrinknames:
# Generate a new unique name and attach it to the symbol. # Generate a new unique name and attach it to the symbol.
unique = self.GenerateLabel() unique = self.GenerateLabel()
self.AddSymbol('l', self.scopeindex, name, NewName=unique) self.AddSymbol('l', self.scopeindex, name, NewName=unique,
ref=0)
else: else:
# Use the existing name. Faster and more readable. # Use the existing name. Faster and more readable.
unique = name unique = name
self.locallabels.add(name) self.locallabels.add(name)
self.AddSymbol('l', self.scopeindex, name) self.AddSymbol('l', self.scopeindex, name, ref=0)
else: else:
# Duplicate labels disallowed. # Duplicate labels disallowed.
@ -1726,7 +1727,7 @@ list lazy_list_set(list L, integer i, list v)
if name in self.locallabels: if name in self.locallabels:
raise EParseDuplicateLabel(self) raise EParseDuplicateLabel(self)
self.locallabels.add(name) self.locallabels.add(name)
self.AddSymbol('l', self.scopeindex, name) self.AddSymbol('l', self.scopeindex, name, ref=0)
self.NextToken() self.NextToken()
self.expect(';') self.expect(';')
self.NextToken() self.NextToken()
@ -1745,6 +1746,7 @@ list lazy_list_set(list L, integer i, list v)
jumpnode)) jumpnode))
else: else:
jumpnode.scope = sym['Scope'] jumpnode.scope = sym['Scope']
sym['ref'] += 1
self.NextToken() self.NextToken()
self.expect(';') self.expect(';')
self.NextToken() self.NextToken()
@ -1833,8 +1835,11 @@ list lazy_list_set(list L, integer i, list v)
# if (a) { while (b) { ... jump label; } @label; } # if (a) { while (b) { ... jump label; } @label; }
self.PushScope() self.PushScope()
self.breakstack.append([self.GenerateLabel(), self.scopeindex, False]) self.breakstack.append([self.GenerateLabel(), self.scopeindex,
self.continuestack.append([self.GenerateLabel(), None, False]) 0])
# Scope still unknown; if a block is opened, Parse_code_block()
# will fill it in.
self.continuestack.append([self.GenerateLabel(), None, 0])
self.expect('(') self.expect('(')
self.NextToken() self.NextToken()
condition = self.Parse_expression() condition = self.Parse_expression()
@ -1862,13 +1867,13 @@ list lazy_list_set(list L, integer i, list v)
assert ret.ch[1].nt == '{}' assert ret.ch[1].nt == '{}'
ret.ch[1].ch.append(nr(nt='@', t=None, name=last[0], ret.ch[1].ch.append(nr(nt='@', t=None, name=last[0],
scope=last[1])) scope=last[1]))
self.AddSymbol('l', last[1], last[0]) self.AddSymbol('l', last[1], last[0], ref=last[2])
last = self.breakstack.pop() last = self.breakstack.pop()
if last[2]: if last[2]:
ret = nr(nt='{}', t=None, ch=[ret, nr(nt='@', t=None, ret = nr(nt='{}', t=None, ch=[ret, nr(nt='@', t=None,
name=last[0], scope=last[1])]) name=last[0], scope=last[1])])
self.AddSymbol('l', last[1], last[0]) self.AddSymbol('l', last[1], last[0], ref=last[2])
self.PopScope() self.PopScope()
return ret return ret
@ -1877,14 +1882,19 @@ list lazy_list_set(list L, integer i, list v)
if self.breakcont: if self.breakcont:
self.PushScope() self.PushScope()
self.breakstack.append([self.GenerateLabel(), self.scopeindex, False]) self.breakstack.append([self.GenerateLabel(), self.scopeindex,
self.continuestack.append([self.GenerateLabel(), None, False]) 0])
# Scope still unknown; if a block is opened, Parse_code_block()
# will fill it in.
self.continuestack.append([self.GenerateLabel(), None, 0])
if self.breakcont and self.tok[0] == '@': if self.breakcont and self.tok[0] == '@':
self.PopScope() self.PopScope()
stmt = self.Parse_statement(ReturnType, AllowStSw = True, InsideLoop = True) stmt = self.Parse_statement(ReturnType, AllowStSw = True,
InsideLoop = True)
self.PushScope() self.PushScope()
else: else:
stmt = self.Parse_statement(ReturnType, AllowStSw = True, InsideLoop = True) stmt = self.Parse_statement(ReturnType, AllowStSw = True,
InsideLoop = True)
self.expect('WHILE') self.expect('WHILE')
self.NextToken() self.NextToken()
self.expect('(') self.expect('(')
@ -1901,13 +1911,13 @@ list lazy_list_set(list L, integer i, list v)
assert ret.ch[0].nt == '{}' assert ret.ch[0].nt == '{}'
ret.ch[0].ch.append(nr(nt='@', t=None, name=last[0], ret.ch[0].ch.append(nr(nt='@', t=None, name=last[0],
scope=last[1])) scope=last[1]))
self.AddSymbol('l', last[1], last[0]) self.AddSymbol('l', last[1], last[0], ref=last[2])
last = self.breakstack.pop() last = self.breakstack.pop()
if last[2]: if last[2]:
ret = nr(nt='{}', t=None, ch=[ret, nr(nt='@', t=None, ret = nr(nt='{}', t=None, ch=[ret, nr(nt='@', t=None,
name=last[0], scope=last[1])]) name=last[0], scope=last[1])])
self.AddSymbol('l', last[1], last[0]) self.AddSymbol('l', last[1], last[0], ref=last[2])
self.PopScope() self.PopScope()
return ret return ret
@ -1916,8 +1926,11 @@ list lazy_list_set(list L, integer i, list v)
if self.breakcont: if self.breakcont:
self.PushScope() self.PushScope()
self.breakstack.append([self.GenerateLabel(), self.scopeindex, False]) self.breakstack.append([self.GenerateLabel(), self.scopeindex,
self.continuestack.append([self.GenerateLabel(), None, False]) 0])
# Scope still unknown; if a block is opened, Parse_code_block()
# will fill it in.
self.continuestack.append([self.GenerateLabel(), None, 0])
self.expect('(') self.expect('(')
self.NextToken() self.NextToken()
initializer = self.Parse_optional_expression_list() initializer = self.Parse_optional_expression_list()
@ -1931,10 +1944,12 @@ list lazy_list_set(list L, integer i, list v)
self.NextToken() self.NextToken()
if self.breakcont and self.tok[0] == '@': if self.breakcont and self.tok[0] == '@':
self.PopScope() self.PopScope()
stmt = self.Parse_statement(ReturnType, AllowStSw = True, InsideLoop = True) stmt = self.Parse_statement(ReturnType, AllowStSw = True,
InsideLoop = True)
self.PushScope() self.PushScope()
else: else:
stmt = self.Parse_statement(ReturnType, AllowStSw = True, InsideLoop = True) stmt = self.Parse_statement(ReturnType, AllowStSw = True,
InsideLoop = True)
ret = nr(nt='FOR', t=None, ret = nr(nt='FOR', t=None,
ch=[nr(nt='EXPRLIST', t=None, ch=initializer), ch=[nr(nt='EXPRLIST', t=None, ch=initializer),
condition, condition,
@ -1947,13 +1962,13 @@ list lazy_list_set(list L, integer i, list v)
assert ret.ch[3].nt == '{}' assert ret.ch[3].nt == '{}'
ret.ch[3].ch.append(nr(nt='@', t=None, name=last[0], ret.ch[3].ch.append(nr(nt='@', t=None, name=last[0],
scope=last[1])) scope=last[1]))
self.AddSymbol('l', last[1], last[0]) self.AddSymbol('l', last[1], last[0], ref=last[2])
last = self.breakstack.pop() last = self.breakstack.pop()
if last[2]: if last[2]:
ret = nr(nt='{}', t=None, ch=[ret, nr(nt='@', t=None, ret = nr(nt='{}', t=None, ch=[ret, nr(nt='@', t=None,
name=last[0], scope=last[1])]) name=last[0], scope=last[1])])
self.AddSymbol('l', last[1], last[0]) self.AddSymbol('l', last[1], last[0], ref=last[2])
self.PopScope() self.PopScope()
return ret return ret
@ -1965,7 +1980,8 @@ list lazy_list_set(list L, integer i, list v)
self.expect(')') self.expect(')')
self.NextToken() self.NextToken()
brk = self.GenerateLabel() brk = self.GenerateLabel()
self.breakstack.append([brk, None, False]) # Scope is determined in Parse_code_block()
self.breakstack.append([brk, None, 0])
blk = self.Parse_code_block(ReturnType, AllowStSw = AllowStSw, blk = self.Parse_code_block(ReturnType, AllowStSw = AllowStSw,
InsideSwitch = True, InsideLoop = InsideLoop) InsideSwitch = True, InsideLoop = InsideLoop)
blkscope = self.breakstack[-1][1] blkscope = self.breakstack[-1][1]
@ -1998,14 +2014,14 @@ list lazy_list_set(list L, integer i, list v)
if blk[idx].nt == 'CASE': if blk[idx].nt == 'CASE':
lbl = self.GenerateLabel() lbl = self.GenerateLabel()
switchcaselist.append((lbl, blk[idx].ch[0])) switchcaselist.append((lbl, blk[idx].ch[0]))
self.AddSymbol('l', blkscope, lbl) self.AddSymbol('l', blkscope, lbl, ref=0)
blk[idx] = nr(nt='@', t=None, name=lbl, scope=blkscope) blk[idx] = nr(nt='@', t=None, name=lbl, scope=blkscope)
elif blk[idx].nt == 'DEFAULTCASE': elif blk[idx].nt == 'DEFAULTCASE':
if switchcasedefault is not None: if switchcasedefault is not None:
raise EParseManyDefaults(self) raise EParseManyDefaults(self)
lbl = self.GenerateLabel() lbl = self.GenerateLabel()
switchcasedefault = lbl switchcasedefault = lbl
self.AddSymbol('l', blkscope, lbl) self.AddSymbol('l', blkscope, lbl, ref=0)
blk[idx] = nr(nt='@', name=lbl, scope=blkscope) blk[idx] = nr(nt='@', name=lbl, scope=blkscope)
prelude = [] prelude = []
@ -2023,6 +2039,7 @@ list lazy_list_set(list L, integer i, list v)
nr(nt='==', t='integer', ch=[lexpr, rexpr]), nr(nt='==', t='integer', ch=[lexpr, rexpr]),
nr(nt='JUMP', t=None, name=case[0], scope=blkscope) nr(nt='JUMP', t=None, name=case[0], scope=blkscope)
])) ]))
self.symtab[blkscope][case[0]]['ref'] += 1
if switchcasedefault is None: if switchcasedefault is None:
if self.errmissingdefault: if self.errmissingdefault:
@ -2034,7 +2051,6 @@ list lazy_list_set(list L, integer i, list v)
# SEF. But we do a preliminary elimination here. # SEF. But we do a preliminary elimination here.
if self.does_something(blk): if self.does_something(blk):
switchcasedefault = brk switchcasedefault = brk
self.breakstack[-1][2] = True
else: else:
# Check if no code up to the default label does anything. # Check if no code up to the default label does anything.
# If so, remove the label and don't generate the jump. # If so, remove the label and don't generate the jump.
@ -2052,10 +2068,16 @@ list lazy_list_set(list L, integer i, list v)
if switchcasedefault is not None: if switchcasedefault is not None:
prelude.append(nr(nt='JUMP', t=None, name=switchcasedefault, prelude.append(nr(nt='JUMP', t=None, name=switchcasedefault,
scope=blkscope)) scope=blkscope))
if switchcasedefault == brk:
# add a reference to it in the break stack
self.breakstack[-1][2] += 1
else:
self.symtab[blkscope][switchcasedefault]['ref'] += 1
last = self.breakstack.pop() last = self.breakstack.pop()
if last[2]: if last[2]:
blk.append(nr(nt='@', name=brk, scope=blkscope)) blk.append(nr(nt='@', name=brk, scope=blkscope))
self.AddSymbol('l', blkscope, brk) self.AddSymbol('l', blkscope, brk, ref=last[2])
return nr(nt='{}', t=None, ch=prelude + blk) return nr(nt='{}', t=None, ch=prelude + blk)
if tok0 == 'CASE': if tok0 == 'CASE':
@ -2104,7 +2126,7 @@ list lazy_list_set(list L, integer i, list v)
self.expect(';') self.expect(';')
self.NextToken() self.NextToken()
try: try:
self.breakstack[n][2] = True self.breakstack[n][2] += 1
except IndexError: except IndexError:
raise EParseInvalidBrkContArg(self) raise EParseInvalidBrkContArg(self)
return nr(nt='JUMP', t=None, name=self.breakstack[n][0], return nr(nt='JUMP', t=None, name=self.breakstack[n][0],
@ -2133,12 +2155,12 @@ list lazy_list_set(list L, integer i, list v)
# Transform to while(cond) while(cond) while(cond) break 2; # Transform to while(cond) while(cond) while(cond) break 2;
# which is equivalent since there are no {}. # which is equivalent since there are no {}.
n += 1 # e.g. -3 -> -2 n += 1 # e.g. -3 -> -2
self.breakstack[n][2] = True # mark the break as used self.breakstack[n][2] += 1 # add a reference to the break
return nr(nt='JUMP', t=None, name=self.breakstack[n][0], return nr(nt='JUMP', t=None, name=self.breakstack[n][0],
scope=self.breakstack[n][1]) scope=self.breakstack[n][1])
except IndexError: except IndexError:
raise EParseInvalidBrkContArg(self) raise EParseInvalidBrkContArg(self)
self.continuestack[n][2] = True self.continuestack[n][2] += 1
return nr(nt='JUMP', t=None, name=self.continuestack[n][0], return nr(nt='JUMP', t=None, name=self.continuestack[n][0],
scope=self.continuestack[n][1]) scope=self.continuestack[n][1])
@ -2544,6 +2566,7 @@ list lazy_list_set(list L, integer i, list v)
self.errorpos = tgt[2] self.errorpos = tgt[2]
raise EParseUndefined(self) raise EParseUndefined(self)
tgt[3].scope = sym['Scope'] tgt[3].scope = sym['Scope']
sym['ref'] += 1
del self.jump_lookups # Finished with it. del self.jump_lookups # Finished with it.