diff options
Diffstat (limited to 'gcc')
| -rw-r--r-- | gcc/tree-ssa-phiopt.cc | 67 |
1 files changed, 36 insertions, 31 deletions
diff --git a/gcc/tree-ssa-phiopt.cc b/gcc/tree-ssa-phiopt.cc index 006c56f..de3d1dd 100644 --- a/gcc/tree-ssa-phiopt.cc +++ b/gcc/tree-ssa-phiopt.cc @@ -3685,31 +3685,55 @@ gate_hoist_loads (void) } /* This pass tries to replaces an if-then-else block with an - assignment. We have four kinds of transformations. Some of these - transformations are also performed by the ifcvt RTL optimizer. + assignment. We have different kinds of transformations. + Some of these transformations are also performed by the ifcvt + RTL optimizer. - Conditional Replacement + PHI-OPT using Match-and-simplify infrastructure ----------------------- - This transformation, implemented in match_simplify_replacement, - replaces + The PHI-OPT pass will try to use match-and-simplify infrastructure + (gimple_simplify) to do transformations. This is implemented in + match_simplify_replacement. + The way it works is it replaces: bb0: if (cond) goto bb2; else goto bb1; bb1: bb2: - x = PHI <0 (bb1), 1 (bb0), ...>; + x = PHI <a (bb1), b (bb0), ...>; - with + with a statement if it gets simplified from `cond ? b : a`. bb0: - x' = cond; - goto bb2; + x1 = cond ? b : a; bb2: - x = PHI <x' (bb0), ...>; + x = PHI <a (bb1), x1 (bb0), ...>; + Bb1 might be removed as it becomes unreachable when doing the replacement. + Though bb1 does not have to be considered a forwarding basic block from bb0. + + Will try to see if `(!cond) ? a : b` gets simplified (iff !cond simplifies); + this is done not to have an explosion of patterns in match.pd. + Note bb1 does not need to be completely empty, it can contain + one statement which is known not to trap. - We remove bb1 as it becomes unreachable. This occurs often due to - gimplification of conditionals. + It also can handle the case where we have two forwarding bbs (diamond): + bb0: + if (cond) goto bb2; else goto bb1; + bb1: goto bb3; + bb2: goto bb3; + bb3: + x = PHI <a (bb1), b (bb2), ...>; + And that is replaced with a statement if it is simplified + from `cond ? b : a`. + Again bb1 and bb2 does not have to be completely empty but + each can contain one statement which is known not to trap. + But in this case bb1/bb2 can only be forwarding basic blocks. + + This fully replaces the old "Conditional Replacement", + "ABS Replacement" transformations as they are now + implmeneted in match.pd. + Some parts of the "MIN/MAX Replacement" are re-implemented in match.pd. Value Replacement ----------------- @@ -3751,25 +3775,6 @@ gate_hoist_loads (void) t3 = t1 & t2; x = a; - ABS Replacement - --------------- - - This transformation, implemented in match_simplify_replacement, replaces - - bb0: - if (a >= 0) goto bb2; else goto bb1; - bb1: - x = -a; - bb2: - x = PHI <x (bb1), a (bb0), ...>; - - with - - bb0: - x' = ABS_EXPR< a >; - bb2: - x = PHI <x' (bb0), ...>; - MIN/MAX Replacement ------------------- |