diff options
| -rw-r--r-- | src/passes/RemoveUnusedBrs.cpp | 90 | ||||
| -rw-r--r-- | test/passes/remove-unused-brs.txt | 57 | ||||
| -rw-r--r-- | test/passes/remove-unused-brs.wast | 56 |
3 files changed, 183 insertions, 20 deletions
diff --git a/src/passes/RemoveUnusedBrs.cpp b/src/passes/RemoveUnusedBrs.cpp index 5b6f0839b..ce839a646 100644 --- a/src/passes/RemoveUnusedBrs.cpp +++ b/src/passes/RemoveUnusedBrs.cpp @@ -607,26 +607,62 @@ struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs>> { list[i] = builder.makeDrop(br1->condition); } } - // combine adjacent br_ifs that test the same value into a br_table, - // when that makes sense + // Combine adjacent br_ifs that test the same value into a br_table, + // when that makes sense. tablify(curr); - // Restructuring of ifs: if we have - // (block $x - // (br_if $x (cond)) - // .., no other references to $x - // ) - // then we can turn that into (if (!cond) ..). - // Code size wise, we turn the block into an if (no change), and - // lose the br_if (-2). .. turns into the body of the if in the binary - // format. We need to flip the condition, which at worst adds 1. - if (curr->name.is()) { - auto* br = list[0]->dynCast<Break>(); - // we seek a regular br_if; if the type is unreachable that means it is not - // actually reached, so ignore - if (br && br->condition && br->name == curr->name && br->type != unreachable) { - assert(!br->value); // can't, it would be dropped or last in the block - if (BranchUtils::BranchSeeker::countNamed(curr, curr->name) == 1) { - // no other breaks to that name, so we can do this + // Pattern-patch ifs, recreating them when it makes sense. + restructureIf(curr); + } + } + + // Restructuring of ifs: if we have + // (block $x + // (br_if $x (cond)) + // .., no other references to $x + // ) + // then we can turn that into (if (!cond) ..). + // Code size wise, we turn the block into an if (no change), and + // lose the br_if (-2). .. turns into the body of the if in the binary + // format. We need to flip the condition, which at worst adds 1. + // If the block has a return value, we can do something similar, removing + // the drop from the br_if and putting the if on the outside, + // (block $x + // (br_if $x (value) (cond)) + // .., no other references to $x + // ..final element.. + // ) + // => + // (if + // (cond) + // (value) ;; must not have side effects! + // (block + // .., no other references to $x + // ..final element.. + // ) + // ) + // This is beneficial as the block will likely go away in the binary + // format (the if arm is an implicit block), and the drop is removed. + void restructureIf(Block* curr) { + auto& list = curr->list; + // We should be called only on potentially-interesting lists. + assert(list.size() >= 2); + if (curr->name.is()) { + Break* br = nullptr; + Drop* drop = list[0]->dynCast<Drop>(); + if (drop) { + br = drop->value->dynCast<Break>(); + } else { + br = list[0]->dynCast<Break>(); + } + // Check if the br is conditional and goes to the block. It may or may not have + // a value, depending on if it was dropped or not. + // If the type is unreachable that means it is not actually reached, + // which we can ignore. + if (br && br->condition && br->name == curr->name && br->type != unreachable) { + if (BranchUtils::BranchSeeker::countNamed(curr, curr->name) == 1) { + // no other breaks to that name, so we can do this + if (!drop) { + assert(!br->value); Builder builder(*getModule()); replaceCurrent(builder.makeIf( builder.makeUnary(EqZInt32, br->condition), @@ -635,7 +671,21 @@ struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs>> { curr->name = Name(); ExpressionManipulator::nop(br); curr->finalize(curr->type); - return; + } else { + // If the items we move around have side effects, we can't do this. + // TODO: we could use a select, in some cases..? + if (!EffectAnalyzer(passOptions, br->value).hasSideEffects() && + !EffectAnalyzer(passOptions, br->condition).hasSideEffects()) { + ExpressionManipulator::nop(list[0]); + Builder builder(*getModule()); + replaceCurrent( + builder.makeIf( + br->condition, + br->value, + curr + ) + ); + } } } } diff --git a/test/passes/remove-unused-brs.txt b/test/passes/remove-unused-brs.txt index b5bcce9f2..03eb7b716 100644 --- a/test/passes/remove-unused-brs.txt +++ b/test/passes/remove-unused-brs.txt @@ -1946,4 +1946,61 @@ ) ) ) + (func $drop-restructure-if (; 81 ;) (type $3) (param $x i32) (param $y i32) (result i32) + (if (result i32) + (get_local $y) + (get_local $x) + (block $label$2 (result i32) + (nop) + (i32.const 0) + ) + ) + ) + (func $drop-restructure-if-final (; 82 ;) (type $3) (param $x i32) (param $y i32) (result i32) + (if (result i32) + (get_local $y) + (get_local $x) + (block $label$2 (result i32) + (nop) + (unreachable) + ) + ) + ) + (func $drop-restructure-if-middle (; 83 ;) (type $3) (param $x i32) (param $y i32) (result i32) + (if (result i32) + (get_local $y) + (get_local $x) + (block $label$2 (result i32) + (nop) + (nop) + (i32.const 0) + ) + ) + ) + (func $drop-restructure-if-bad (; 84 ;) (type $3) (param $x i32) (param $y i32) (result i32) + (block $label$2 (result i32) + (drop + (br_if $label$2 + (tee_local $y + (get_local $x) + ) + (get_local $y) + ) + ) + (i32.const 0) + ) + ) + (func $drop-restructure-if-bad-2 (; 85 ;) (type $3) (param $x i32) (param $y i32) (result i32) + (block $label$2 (result i32) + (drop + (br_if $label$2 + (get_local $y) + (tee_local $y + (get_local $x) + ) + ) + ) + (i32.const 0) + ) + ) ) diff --git a/test/passes/remove-unused-brs.wast b/test/passes/remove-unused-brs.wast index 8325b47ac..7f77fd00c 100644 --- a/test/passes/remove-unused-brs.wast +++ b/test/passes/remove-unused-brs.wast @@ -1561,5 +1561,61 @@ ) ) ) + (func $drop-restructure-if (param $x i32) (param $y i32) (result i32) + (block $label$2 (result i32) + (drop + (br_if $label$2 + (get_local $x) + (get_local $y) + ) + ) + (i32.const 0) + ) + ) + (func $drop-restructure-if-final (param $x i32) (param $y i32) (result i32) + (block $label$2 (result i32) + (drop + (br_if $label$2 + (get_local $x) + (get_local $y) + ) + ) + (unreachable) + ) + ) + (func $drop-restructure-if-middle (param $x i32) (param $y i32) (result i32) + (block $label$2 (result i32) + (drop + (br_if $label$2 + (get_local $x) + (get_local $y) + ) + ) + (nop) ;; the middle + (i32.const 0) + ) + ) + (func $drop-restructure-if-bad (param $x i32) (param $y i32) (result i32) + (block $label$2 (result i32) + (drop + (br_if $label$2 + (tee_local $y (get_local $x)) + (get_local $y) + ) + ) + (i32.const 0) + ) + ) + (func $drop-restructure-if-bad-2 (param $x i32) (param $y i32) (result i32) + (block $label$2 (result i32) + (drop + (br_if $label$2 + (get_local $y) + (tee_local $y (get_local $x)) + ) + ) + (i32.const 0) + ) + ) ) |