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-rw-r--r--src/passes/RemoveUnusedBrs.cpp26
-rw-r--r--test/emcc_hello_world.fromasm22
-rw-r--r--test/emcc_hello_world.fromasm.imprecise22
-rw-r--r--test/passes/remove-unused-brs.txt83
-rw-r--r--test/passes/remove-unused-brs.wast60
5 files changed, 183 insertions, 30 deletions
diff --git a/src/passes/RemoveUnusedBrs.cpp b/src/passes/RemoveUnusedBrs.cpp
index 924cd7848..8b7611ec9 100644
--- a/src/passes/RemoveUnusedBrs.cpp
+++ b/src/passes/RemoveUnusedBrs.cpp
@@ -25,6 +25,16 @@
namespace wasm {
+// to turn an if into a br-if, we must be able to reorder the
+// condition and possible value, and the possible value must
+// not have side effects (as they would run unconditionally)
+static bool canTurnIfIntoBrIf(Expression* ifCondition, Expression* brValue) {
+ if (!brValue) return true;
+ EffectAnalyzer value(brValue);
+ if (value.hasSideEffects()) return false;
+ return !EffectAnalyzer(ifCondition).invalidates(value);
+}
+
struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs, Visitor<RemoveUnusedBrs>>> {
bool isFunctionParallel() override { return true; }
@@ -137,15 +147,11 @@ struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs, Visitor<R
Break* br = curr->ifTrue->dynCast<Break>();
if (br && !br->condition) { // TODO: if there is a condition, join them
// if the br has a value, then if => br_if means we always execute the value, and also the order is value,condition vs condition,value
- if (br->value) {
- EffectAnalyzer value(br->value);
- if (value.hasSideEffects()) return;
- EffectAnalyzer condition(curr->condition);
- if (condition.invalidates(value)) return;
+ if (canTurnIfIntoBrIf(curr->condition, br->value)) {
+ br->condition = curr->condition;
+ replaceCurrent(br);
+ anotherCycle = true;
}
- br->condition = curr->condition;
- replaceCurrent(br);
- anotherCycle = true;
}
}
// TODO: if-else can be turned into a br_if as well, if one of the sides is a dead end
@@ -398,7 +404,7 @@ struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs, Visitor<R
auto* iff = list[i]->dynCast<If>();
if (!iff || !iff->ifFalse || isConcreteWasmType(iff->type)) continue; // if it lacked an if-false, it would already be a br_if, as that's the easy case
auto* ifTrueBreak = iff->ifTrue->dynCast<Break>();
- if (ifTrueBreak && !ifTrueBreak->condition) {
+ if (ifTrueBreak && !ifTrueBreak->condition && canTurnIfIntoBrIf(iff->condition, ifTrueBreak->value)) {
// we are an if-else where the ifTrue is a break without a condition, so we can do this
list[i] = ifTrueBreak;
ifTrueBreak->condition = iff->condition;
@@ -407,7 +413,7 @@ struct RemoveUnusedBrs : public WalkerPass<PostWalker<RemoveUnusedBrs, Visitor<R
}
// otherwise, perhaps we can flip the if
auto* ifFalseBreak = iff->ifFalse->dynCast<Break>();
- if (ifFalseBreak && !ifFalseBreak->condition) {
+ if (ifFalseBreak && !ifFalseBreak->condition && canTurnIfIntoBrIf(iff->condition, ifFalseBreak->value)) {
list[i] = ifFalseBreak;
ifFalseBreak->condition = Builder(*getModule()).makeUnary(EqZInt32, iff->condition);
ExpressionManipulator::spliceIntoBlock(curr, i + 1, iff->ifTrue);
diff --git a/test/emcc_hello_world.fromasm b/test/emcc_hello_world.fromasm
index 4680aea58..9f0d1ee47 100644
--- a/test/emcc_hello_world.fromasm
+++ b/test/emcc_hello_world.fromasm
@@ -3252,9 +3252,8 @@
(get_local $7)
)
)
- (br_if $label$break$L46
- (get_local $5)
- (i32.ge_u
+ (if
+ (i32.lt_u
(tee_local $9
(i32.add
(i32.load8_s
@@ -3270,15 +3269,18 @@
)
(i32.const 10)
)
- )
- (block
- (set_local $10
- (get_local $7)
+ (block
+ (set_local $10
+ (get_local $7)
+ )
+ (set_local $7
+ (get_local $9)
+ )
+ (br $while-in$18)
)
- (set_local $7
- (get_local $9)
+ (br $label$break$L46
+ (get_local $5)
)
- (br $while-in$18)
)
)
)
diff --git a/test/emcc_hello_world.fromasm.imprecise b/test/emcc_hello_world.fromasm.imprecise
index 66c49ce29..88532cef3 100644
--- a/test/emcc_hello_world.fromasm.imprecise
+++ b/test/emcc_hello_world.fromasm.imprecise
@@ -3245,9 +3245,8 @@
(get_local $7)
)
)
- (br_if $label$break$L46
- (get_local $5)
- (i32.ge_u
+ (if
+ (i32.lt_u
(tee_local $9
(i32.add
(i32.load8_s
@@ -3263,15 +3262,18 @@
)
(i32.const 10)
)
- )
- (block
- (set_local $10
- (get_local $7)
+ (block
+ (set_local $10
+ (get_local $7)
+ )
+ (set_local $7
+ (get_local $9)
+ )
+ (br $while-in$18)
)
- (set_local $7
- (get_local $9)
+ (br $label$break$L46
+ (get_local $5)
)
- (br $while-in$18)
)
)
)
diff --git a/test/passes/remove-unused-brs.txt b/test/passes/remove-unused-brs.txt
index 9eb413294..94b214588 100644
--- a/test/passes/remove-unused-brs.txt
+++ b/test/passes/remove-unused-brs.txt
@@ -3,6 +3,7 @@
(type $0 (func (param i32)))
(type $1 (func))
(type $2 (func (result i32)))
+ (type $3 (func (param i32 i32) (result i32)))
(func $b0-yes (type $0) (param $i1 i32)
(block $topmost
)
@@ -760,4 +761,86 @@
)
)
)
+ (func $if-to-br_if-conflict (type $3) (param $x i32) (param $y i32) (result i32)
+ (block $leave
+ (set_local $y
+ (block $out
+ (if
+ (get_local $x)
+ (br $out
+ (block $block1
+ (set_local $x
+ (i32.const 0)
+ )
+ (i32.const 1)
+ )
+ )
+ (br_if $leave
+ (i32.const 1)
+ )
+ )
+ (unreachable)
+ )
+ )
+ )
+ (i32.add
+ (get_local $x)
+ (get_local $y)
+ )
+ )
+ (func $if-to-br_if-conflict2 (type $3) (param $x i32) (param $y i32) (result i32)
+ (block $leave
+ (set_local $y
+ (block $out
+ (if
+ (get_local $x)
+ (br_if $leave
+ (i32.const 1)
+ )
+ (br $out
+ (block $block2
+ (set_local $x
+ (i32.const 0)
+ )
+ (i32.const 1)
+ )
+ )
+ )
+ (unreachable)
+ )
+ )
+ )
+ (i32.add
+ (get_local $x)
+ (get_local $y)
+ )
+ )
+ (func $if-to-br_if-value-sideeffect (type $3) (param $x i32) (param $y i32) (result i32)
+ (block $leave
+ (set_local $y
+ (block $out
+ (if
+ (get_local $x)
+ (br $out
+ (block $block1
+ (drop
+ (call $if-to-br_if-value-sideeffect
+ (i32.const 0)
+ (i32.const 1)
+ )
+ )
+ (nop)
+ (i32.const 1)
+ )
+ )
+ )
+ (unreachable)
+ )
+ )
+ )
+ (i32.add
+ (get_local $x)
+ (get_local $y)
+ )
+ )
)
diff --git a/test/passes/remove-unused-brs.wast b/test/passes/remove-unused-brs.wast
index e777efa5b..ecbcb6caa 100644
--- a/test/passes/remove-unused-brs.wast
+++ b/test/passes/remove-unused-brs.wast
@@ -700,4 +700,64 @@
(br $stack1)
)
)
+ (func $if-to-br_if-conflict (param $x i32) (param $y i32) (result i32)
+ (block $leave
+ (set_local $y
+ (block $out
+ (if
+ (get_local $x)
+ (br $out
+ (block
+ (set_local $x (i32.const 0))
+ (i32.const 1)
+ )
+ )
+ (br_if $leave (i32.const 1))
+ )
+ (unreachable)
+ )
+ )
+ )
+ (i32.add (get_local $x) (get_local $y))
+ )
+ (func $if-to-br_if-conflict2 (param $x i32) (param $y i32) (result i32)
+ (block $leave
+ (set_local $y
+ (block $out
+ (if
+ (get_local $x)
+ (br_if $leave (i32.const 1))
+ (br $out
+ (block
+ (set_local $x (i32.const 0))
+ (i32.const 1)
+ )
+ )
+ )
+ (unreachable)
+ )
+ )
+ )
+ (i32.add (get_local $x) (get_local $y))
+ )
+ (func $if-to-br_if-value-sideeffect (param $x i32) (param $y i32) (result i32)
+ (block $leave
+ (set_local $y
+ (block $out
+ (if
+ (get_local $x)
+ (br $out
+ (block
+ (drop (call $if-to-br_if-value-sideeffect (i32.const 0) (i32.const 1)))
+ (nop)
+ (i32.const 1)
+ )
+ )
+ )
+ (unreachable)
+ )
+ )
+ )
+ (i32.add (get_local $x) (get_local $y))
+ )
)
generated by cgit v1.2.3 (git 2.39.1) at 2025-08-07 23:36:47 +0000