Merge pull request #12672 from ethereum/redundantStoreEliminatorLimited

Redundant store eliminator limited

Author: chriseth

Changelog.md

@@ -7,6 +7,7 @@ Language Features:
 Compiler Features:
 * JSON-AST: Added selector field for errors and events.
  * Peephole Optimizer: Optimize comparisons in front of conditional jumps and conditional jumps across a single unconditional jump.
+ * Yul Optimizer: Remove ``sstore`` and ``mstore`` operations that are never read from.
 
 Bugfixes:
  * Yul IR Code Generation: Optimize embedded creation code with correct settings. This fixes potential mismatches between the constructor code of a contract compiled in isolation and the bytecode in ``type(C).creationCode``, resp. the bytecode used for ``new C(...)``.

libevmasm/SemanticInformation.cpp

@@ -121,7 +121,9 @@ vector<SemanticInformation::Operation> SemanticInformation::readWriteOperations(
 			Location::Memory,
 			Effect::Write,
 			paramCount - 2,
-			paramCount - 1,
+			// Length is in paramCount - 1, but it is only a max length,
+			// there is no guarantee that the full area is written to.
+			{},
 			{}
 		});
 		return operations;

libsolidity/interface/OptimiserSettings.h

@@ -55,7 +55,7 @@ struct OptimiserSettings
 			"xa[rul]"                  // Prune a bit more in SSA
 			"xa[r]cL"                  // Turn into SSA again and simplify
 			"gvif"                     // Run full inliner
-			"CTUca[r]LsTFOtfDnca[r]Iulc" // SSA plus simplify
+			"CTUca[r]LSsTFOtfDnca[r]Iulc" // SSA plus simplify
 		"]"
 		"jmul[jul] VcTOcul jmul";      // Make source short and pretty
 

libyul/CMakeLists.txt

@@ -179,6 +179,8 @@ add_library(yul
 	optimiser/UnusedAssignEliminator.h
 	optimiser/UnusedStoreBase.cpp
 	optimiser/UnusedStoreBase.h
+	optimiser/UnusedStoreEliminator.cpp
+	optimiser/UnusedStoreEliminator.h
 	optimiser/Rematerialiser.cpp
 	optimiser/Rematerialiser.h
 	optimiser/SMTSolver.cpp

libyul/optimiser/Suite.cpp

@@ -57,6 +57,7 @@
 #include <libyul/optimiser/StructuralSimplifier.h>
 #include <libyul/optimiser/SyntacticalEquality.h>
 #include <libyul/optimiser/UnusedAssignEliminator.h>
+#include <libyul/optimiser/UnusedStoreEliminator.h>
 #include <libyul/optimiser/VarNameCleaner.h>
 #include <libyul/optimiser/LoadResolver.h>
 #include <libyul/optimiser/LoopInvariantCodeMotion.h>
@@ -222,6 +223,7 @@ map<string, unique_ptr<OptimiserStep>> const& OptimiserSuite::allSteps()
 			LoadResolver,
 			LoopInvariantCodeMotion,
 			UnusedAssignEliminator,
+			UnusedStoreEliminator,
 			ReasoningBasedSimplifier,
 			Rematerialiser,
 			SSAReverser,
@@ -264,6 +266,7 @@ map<string, char> const& OptimiserSuite::stepNameToAbbreviationMap()
 		{LoopInvariantCodeMotion::name,       'M'},
 		{ReasoningBasedSimplifier::name,      'R'},
 		{UnusedAssignEliminator::name,        'r'},
+		{UnusedStoreEliminator::name,         'S'},
 		{Rematerialiser::name,                'm'},
 		{SSAReverser::name,                   'V'},
 		{SSATransform::name,                  'a'},