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authorchriseth <chris@ethereum.org>2018-12-12 07:49:36 +0800
committerchriseth <chris@ethereum.org>2018-12-13 01:06:28 +0800
commit9557dd7e74a801ebafaf4777d60a591b0c484779 (patch)
treeb55af218e8debaeb4a79670f932e1e66afb736b6
parent5e0c312dad2daaae155486397bfbd26d6d172718 (diff)
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Support unassigned variables in the SSA value tracker and the data flow analyzer.
-rw-r--r--libyul/optimiser/DataFlowAnalyzer.cpp9
-rw-r--r--libyul/optimiser/DataFlowAnalyzer.h2
-rw-r--r--libyul/optimiser/SSAValueTracker.cpp9
-rw-r--r--libyul/optimiser/SSAValueTracker.h2
-rw-r--r--test/libyul/yulOptimizerTests/commonSubexpressionEliminator/unassigned_variables.yul14
-rw-r--r--test/libyul/yulOptimizerTests/expressionSimplifier/unassigend_vars_multi.yul5
-rw-r--r--test/libyul/yulOptimizerTests/expressionSimplifier/unassigned_vars.yul5
-rw-r--r--test/libyul/yulOptimizerTests/fullInliner/large_function_multi_use.yul13
-rw-r--r--test/libyul/yulOptimizerTests/structuralSimplifier/if_multi_unassigned_condition.yul10
-rw-r--r--test/libyul/yulOptimizerTests/structuralSimplifier/if_unassigned_condition.yul9
10 files changed, 65 insertions, 13 deletions
diff --git a/libyul/optimiser/DataFlowAnalyzer.cpp b/libyul/optimiser/DataFlowAnalyzer.cpp
index 64c67b38..7bff2c89 100644
--- a/libyul/optimiser/DataFlowAnalyzer.cpp
+++ b/libyul/optimiser/DataFlowAnalyzer.cpp
@@ -136,17 +136,22 @@ void DataFlowAnalyzer::operator()(Block& _block)
void DataFlowAnalyzer::handleAssignment(set<YulString> const& _variables, Expression* _value)
{
+ static Expression const zero{Literal{{}, LiteralKind::Number, YulString{"0"}, {}}};
clearValues(_variables);
MovableChecker movableChecker;
if (_value)
movableChecker.visit(*_value);
- if (_variables.size() == 1)
+ else
+ for (auto const& var: _variables)
+ m_value[var] = &zero;
+
+ if (_value && _variables.size() == 1)
{
YulString name = *_variables.begin();
// Expression has to be movable and cannot contain a reference
// to the variable that will be assigned to.
- if (_value && movableChecker.movable() && !movableChecker.referencedVariables().count(name))
+ if (movableChecker.movable() && !movableChecker.referencedVariables().count(name))
m_value[name] = _value;
}
diff --git a/libyul/optimiser/DataFlowAnalyzer.h b/libyul/optimiser/DataFlowAnalyzer.h
index cd134d48..4f12ff6a 100644
--- a/libyul/optimiser/DataFlowAnalyzer.h
+++ b/libyul/optimiser/DataFlowAnalyzer.h
@@ -36,6 +36,8 @@ namespace yul
* Tracks assignments and is used as base class for both Rematerialiser and
* Common Subexpression Eliminator.
*
+ * A special zero constant expression is used for the default value of variables.
+ *
* Prerequisite: Disambiguator
*/
class DataFlowAnalyzer: public ASTModifier
diff --git a/libyul/optimiser/SSAValueTracker.cpp b/libyul/optimiser/SSAValueTracker.cpp
index ef96c379..a0e44b2b 100644
--- a/libyul/optimiser/SSAValueTracker.cpp
+++ b/libyul/optimiser/SSAValueTracker.cpp
@@ -35,11 +35,12 @@ void SSAValueTracker::operator()(Assignment const& _assignment)
void SSAValueTracker::operator()(VariableDeclaration const& _varDecl)
{
- if (_varDecl.variables.size() == 1)
- setValue(_varDecl.variables.front().name, _varDecl.value.get());
- else if (!_varDecl.value)
+ static Expression const zero{Literal{{}, LiteralKind::Number, YulString{"0"}, {}}};
+ if (!_varDecl.value)
for (auto const& var: _varDecl.variables)
- setValue(var.name, nullptr);
+ setValue(var.name, &zero);
+ else if (_varDecl.variables.size() == 1)
+ setValue(_varDecl.variables.front().name, _varDecl.value.get());
}
void SSAValueTracker::setValue(YulString _name, Expression const* _value)
diff --git a/libyul/optimiser/SSAValueTracker.h b/libyul/optimiser/SSAValueTracker.h
index efec2200..0a6cde80 100644
--- a/libyul/optimiser/SSAValueTracker.h
+++ b/libyul/optimiser/SSAValueTracker.h
@@ -33,7 +33,7 @@ namespace yul
* Class that walks the AST and stores the initial value of each variable
* that is never assigned to.
*
- * Default value is represented as nullptr.
+ * A special zero constant expression is used for the default value of variables.
*
* Prerequisite: Disambiguator
*/
diff --git a/test/libyul/yulOptimizerTests/commonSubexpressionEliminator/unassigned_variables.yul b/test/libyul/yulOptimizerTests/commonSubexpressionEliminator/unassigned_variables.yul
new file mode 100644
index 00000000..a790ca65
--- /dev/null
+++ b/test/libyul/yulOptimizerTests/commonSubexpressionEliminator/unassigned_variables.yul
@@ -0,0 +1,14 @@
+{
+ // This does not replace b by a because there is no
+ // explicit assignment, even though both hold the same value.
+ let a
+ let b
+ mstore(sub(a, b), 7)
+}
+// ----
+// commonSubexpressionEliminator
+// {
+// let a
+// let b
+// mstore(sub(a, b), 7)
+// }
diff --git a/test/libyul/yulOptimizerTests/expressionSimplifier/unassigend_vars_multi.yul b/test/libyul/yulOptimizerTests/expressionSimplifier/unassigend_vars_multi.yul
index 8c1ad789..f260db0b 100644
--- a/test/libyul/yulOptimizerTests/expressionSimplifier/unassigend_vars_multi.yul
+++ b/test/libyul/yulOptimizerTests/expressionSimplifier/unassigend_vars_multi.yul
@@ -1,5 +1,4 @@
-// c & d can't be optimized as expression simplifier doesn't handle default
-// values yet
+// Unassigned variables are assumed to be zero.
{
let c, d
let y := add(d, add(c, 7))
@@ -8,5 +7,5 @@
// expressionSimplifier
// {
// let c, d
-// let y := add(add(d, c), 7)
+// let y := 7
// }
diff --git a/test/libyul/yulOptimizerTests/expressionSimplifier/unassigned_vars.yul b/test/libyul/yulOptimizerTests/expressionSimplifier/unassigned_vars.yul
index 87391b8c..7b1430f3 100644
--- a/test/libyul/yulOptimizerTests/expressionSimplifier/unassigned_vars.yul
+++ b/test/libyul/yulOptimizerTests/expressionSimplifier/unassigned_vars.yul
@@ -1,5 +1,4 @@
-// c & d can't be optimized as expression simplifier doesn't handle default
-// values yet
+// Unassigned variables are assumed to be zero.
{
let c
let d
@@ -10,5 +9,5 @@
// {
// let c
// let d
-// let y := add(add(d, c), 7)
+// let y := 7
// }
diff --git a/test/libyul/yulOptimizerTests/fullInliner/large_function_multi_use.yul b/test/libyul/yulOptimizerTests/fullInliner/large_function_multi_use.yul
index 0972ac56..ec44dafb 100644
--- a/test/libyul/yulOptimizerTests/fullInliner/large_function_multi_use.yul
+++ b/test/libyul/yulOptimizerTests/fullInliner/large_function_multi_use.yul
@@ -13,6 +13,9 @@
let r := f(a)
// This should be inlined because it is a constant
let t := f(a2)
+ let a3
+ // This should be inlined because it is a constant as well (zero)
+ let s := f(a3)
}
// ----
// fullInliner
@@ -30,6 +33,16 @@
// let f_y := add(f_a, f_x)
// sstore(f_y, 10)
// let t := f_b
+// let a3
+// let f_a_5 := a3
+// let f_b_6
+// let f_x_7 := mload(f_a_5)
+// f_b_6 := sload(f_x_7)
+// let f_c_8 := 3
+// mstore(mul(f_a_5, f_b_6), mload(f_x_7))
+// let f_y_11 := add(f_a_5, f_x_7)
+// sstore(f_y_11, 10)
+// let s := f_b_6
// }
// function f(a) -> b
// {
diff --git a/test/libyul/yulOptimizerTests/structuralSimplifier/if_multi_unassigned_condition.yul b/test/libyul/yulOptimizerTests/structuralSimplifier/if_multi_unassigned_condition.yul
new file mode 100644
index 00000000..0ece5dbd
--- /dev/null
+++ b/test/libyul/yulOptimizerTests/structuralSimplifier/if_multi_unassigned_condition.yul
@@ -0,0 +1,10 @@
+{
+ let x, y
+ if x { mstore(0, 0) }
+ if y { mstore(0, 0) }
+}
+// ----
+// structuralSimplifier
+// {
+// let x, y
+// }
diff --git a/test/libyul/yulOptimizerTests/structuralSimplifier/if_unassigned_condition.yul b/test/libyul/yulOptimizerTests/structuralSimplifier/if_unassigned_condition.yul
new file mode 100644
index 00000000..a327a882
--- /dev/null
+++ b/test/libyul/yulOptimizerTests/structuralSimplifier/if_unassigned_condition.yul
@@ -0,0 +1,9 @@
+{
+ let x
+ if x { mstore(0, 0) }
+}
+// ----
+// structuralSimplifier
+// {
+// let x
+// }