Combine multiple shifts with constant shift-by values in the optimiser

Changelog.md

@@ -7,6 +7,7 @@ Compiler Features:
  * SMTChecker: Do not report underflow/overflow if they always revert. This removes false positives when using ``SafeMath``.
  * Static Analyzer: Warn about expressions with custom types when they have no effect.
  * Optimizer: Add rule for shifts with constants for Constantinople.
+ * Optimizer: Combine multiple shifts with constant shift-by values into one.
  * Optimizer: Support shifts in the constant optimiser for Constantinople.
 
 

libevmasm/RuleList.h

@@ -24,6 +24,8 @@
 #include <vector>
 #include <functional>
 
+#include <boost/multiprecision/detail/min_max.hpp>
+
 #include <libevmasm/Instruction.h>
 #include <libevmasm/SimplificationRule.h>
 
@@ -336,6 +338,20 @@ std::vector<SimplificationRule<Pattern>> simplificationRuleListPart7(
 		}
 	}
 
+	rules.push_back({
+		// SHL(B, SHL(A, X)) -> SHL(min(A+B, 256), X)
+		{Instruction::SHL, {{B}, {Instruction::SHL, {{A}, {X}}}}},
+		[=]() -> Pattern { return {Instruction::SHL, {std::min(A.d() + B.d(), u256(256)), X}}; },
+		false
+	});
+
+	rules.push_back({
+		// SHR(B, SHR(A, X)) -> SHR(min(A+B, 256), X)
+		{Instruction::SHR, {{B}, {Instruction::SHR, {{A}, {X}}}}},
+		[=]() -> Pattern { return {Instruction::SHR, {std::min(A.d() + B.d(), u256(256)), X}}; },
+		false
+	});
+
 	return rules;
 }