Previously pi placement happened after initial phi placement.
Afterwards a second phi placement pass was performed, however it
incorrectly only placed phis on the dominance frontier, rather
than the iterated dominance frontier.
This is fixed by moving pi placement before the propagation of
defs on the iterated DFs, and adding a def for each added pi.
While this ensures that we generate correct conservative SSA, there
is still one remaining case in which we may generate non-minimal
SSA form. Consider:
|1|
|pi
v
|2|<--\
| |
\----/
The pi is semanically located along the edge 1->2, however we place
it (and its def point) in 2, thus leading to the generation of an
additional (trivial) phi in 2.
Conflicts:
ext/opcache/Optimizer/zend_ssa.c
This interdependence is problematic because we can't propagate pi
def points in the initial dominance frontier propagation. The used
rule for multiple-predecessor blocks may also miss cases where
placing the pi would have been useful.
The new heuristic for pi placement checks that a) the variable is
live-in and b) for the "from" block that generated the pi, the
other successor does not dominate all other predecessors of the
"to" block.
The purpose of case b) may be illustrated with an example:
if (is_int($i)) {
// place pi here
}
// but don't place pi here
The reason we do not want to place the second pi is that we generally
place pis in positive+negative pairs, and in this case the pair
would merge in a phi and cancel out, so we get no useful information
out of it.
For live-variable analysis it does not matter if def includes
variables that are previously use in the same block, the data flow
equations still have the same result. As such there is no need to
compute separate gen & def sets.
I'm keeping the name "def", because use of "gen" in this context is
pretty confusing (gen is usually the use set, not the def set).
Instead decide whether a function returned by reference or by value
by checking whether the return value has REFERENCE type. This means
that functions returning by reference must always return a reference
and functions returning by value must not return a reference.
Squashed commit of the following:
commit e05d3b6732
Author: Andrea Faulds <ajf@ajf.me>
Date: Wed Mar 30 01:43:35 2016 +0100
UPGRADING and NEWS
commit 6caf1d4585
Author: Andrea Faulds <ajf@ajf.me>
Date: Sun Mar 20 21:18:33 2016 +0000
Fixes
commit 6dadb1b0ef
Author: Andrea Faulds <ajf@ajf.me>
Date: Sun Feb 14 02:15:01 2016 +0000
Add test for numeric string errors in assignment
commit bd5f04e8dd
Author: Andrea Faulds <ajf@ajf.me>
Date: Sat Feb 13 23:53:05 2016 +0000
Add test for numeric string errors
commit c72e92f16d
Author: Andrea Faulds <ajf@ajf.me>
Date: Tue Jan 26 23:28:33 2016 +0000
Add test for scientific notation in integer operations
commit d94c08852d
Author: Andrea Faulds <ajf@ajf.me>
Date: Sun Feb 14 01:25:57 2016 +0000
Disable optimiser evaluation for numeric string errors
commit 30ee954ed1
Author: Andrea Faulds <ajf@ajf.me>
Date: Sun Feb 14 01:46:25 2016 +0000
fixup
commit a6403b79e0
Author: Andrea Faulds <ajf@ajf.me>
Date: Sat Feb 13 22:00:27 2016 +0000
Do not convert error-causing numeric strings ahead-of-time
commit f9dc354014
Author: Andrea Faulds <ajf@ajf.me>
Date: Sat Feb 13 19:15:38 2016 +0000
Disable compile-time evaluation for numeric string errors
commit e05b0cc849
Author: Andrea Faulds <ajf@ajf.me>
Date: Fri Feb 5 11:42:26 2016 +0000
Make _zval_get_long_func_noisy function for inlining
commit 84d66321a5
Author: Andrea Faulds <ajf@ajf.me>
Date: Tue Jan 26 23:10:00 2016 +0000
Update tests
commit 5ac4a0cc4b
Author: Andrea Faulds <ajf@ajf.me>
Date: Tue Jan 26 22:08:19 2016 +0000
Use is_numeric_string_ex for zval_get_long etc.
commit c21f088485
Author: Andrea Faulds <ajf@ajf.me>
Date: Thu Jan 7 21:13:04 2016 +0000
Update tests
commit 63e214cf81
Author: Andrea Faulds <ajf@ajf.me>
Date: Wed Jan 6 00:28:01 2016 +0000
Warn on non-/bad numeric strings in arithmetic
Nikita Popov