[move compiler] common subexpression elimination

Author: junxzm1990

third_party/move/move-compiler-v2/src/experiments.rs

@@ -162,6 +162,11 @@ pub static EXPERIMENTS: Lazy<BTreeMap<String, Experiment>> = Lazy::new(|| {
             description: "Turns on optimizations waiting for comparison testing".to_string(),
             default: Given(false),
         },
+        Experiment {
+            name: Experiment::COMMON_SUBEXP_ELIMINATION.to_string(),
+            description: "Whether to run common subexpression elimination".to_string(),
+            default: Inherited(Experiment::OPTIMIZE_WAITING_FOR_COMPARE_TESTS.to_string()),
+        },
         Experiment {
             name: Experiment::CFG_SIMPLIFICATION.to_string(),
             description: "Whether to do the control flow graph simplification".to_string(),
@@ -322,6 +327,7 @@ impl Experiment {
     pub const CFG_SIMPLIFICATION: &'static str = "cfg-simplification";
     pub const CHECKS: &'static str = "checks";
     pub const CMP_REWRITE: &'static str = "cmp-rewrite";
+    pub const COMMON_SUBEXP_ELIMINATION: &'static str = "common-subexp-elimination";
     pub const COMPILE_FOR_TESTING: &'static str = "compile-for-testing";
     pub const DEAD_CODE_ELIMINATION: &'static str = "dead-code-elimination";
     pub const DUPLICATE_STRUCT_PARAMS_CHECK: &'static str = "duplicate-struct-params-check";

third_party/move/move-compiler-v2/src/lib.rs

@@ -25,12 +25,14 @@ use crate::{
     },
     pipeline::{
         ability_processor::AbilityProcessor,
+        common_subexp_elimination::CommonSubexpElimination,
         control_flow_graph_simplifier::ControlFlowGraphSimplifier,
         dead_store_elimination::DeadStoreElimination,
         exit_state_analysis::ExitStateAnalysisProcessor,
         flush_writes_processor::FlushWritesProcessor,
         lint_processor::LintProcessor,
         livevar_analysis_processor::LiveVarAnalysisProcessor,
+        reaching_def_analysis_processor::ReachingDefProcessor,
         reference_safety::{reference_safety_processor_v2, reference_safety_processor_v3},
         split_critical_edges_processor::SplitCriticalEdgesProcessor,
         uninitialized_use_checker::UninitializedUseChecker,
@@ -556,6 +558,26 @@ pub fn stackless_bytecode_optimization_pipeline(options: &Options) -> FunctionTa
         pipeline.add_processor(Box::new(SplitCriticalEdgesProcessor {}));
     }
 
+    // Common subexpression elimination
+    // Need to run before `ABILITY_CHECK`
+    // Further, all annotations are clearned after this pass
+    if options.experiment_on(Experiment::COMMON_SUBEXP_ELIMINATION) {
+        // analysis dependecy: live_var -> reference_safety -> reaching_def -> common_subexp_elimination
+        pipeline.add_processor(Box::new(LiveVarAnalysisProcessor::new(true)));
+        pipeline.add_processor(Box::new(FlushWritesProcessor {}));
+        if options.experiment_on(Experiment::REFERENCE_SAFETY_V3) {
+            pipeline.add_processor(Box::new(
+                reference_safety_processor_v3::ReferenceSafetyProcessor {},
+            ));
+        } else {
+            pipeline.add_processor(Box::new(
+                reference_safety_processor_v2::ReferenceSafetyProcessor {},
+            ));
+        }
+        pipeline.add_processor(Box::new(ReachingDefProcessor {}));
+        pipeline.add_processor(Box::new(CommonSubexpElimination::new(true)));
+    }
+
     // Reference safety checkers need live variable annotation.
     pipeline.add_processor(Box::new(LiveVarAnalysisProcessor::new(false)));
     if options.experiment_on(Experiment::REFERENCE_SAFETY_V3) {