the revive-explorer utility (#364)

A maintainable and more precise version of what was a hacky but useful
script, exploring the compilers YUL lowering unit.

It analyzes a given shared objects from the debug dump and outputs:
- The count of each YUL statement translated.
- A per YUL statement break-down of bytecode size contributed per.
- Estimated `yul-phaser` cost parameters.

Signed-off-by: Cyrill Leutwiler <bigcyrill@hotmail.com>

crates/explorer/src/dwarfdump_analyzer.rs

@@ -0,0 +1,250 @@
+//! The core dwarf dump analyzer library.
+
+use std::{
+    collections::HashMap,
+    path::{Path, PathBuf},
+};
+
+use revive_yul::lexer::token::location::Location;
+
+use crate::location_mapper::{self, map_locations, LocationMap};
+
+/// Unknwon code.
+pub const OTHER: &str = "other";
+/// Compiler internal code.
+pub const INTERNAL: &str = "internal";
+/// YUL block code.
+pub const BLOCK: &str = "block";
+/// YUL function call code.
+pub const FUNCTION_CALL: &str = "function_call";
+/// YUL conditional code.
+pub const IF: &str = "if";
+/// YUL loop code.
+pub const FOR: &str = "for";
+/// YUL loop continue code.
+pub const CONTINUE: &str = "continue";
+/// YUL loop break code.
+pub const BREAK: &str = "break";
+/// YUL switch code.
+pub const SWITCH: &str = "switch";
+/// YUL variable declaration code.
+pub const DECLARATION: &str = "let";
+/// YUL variable assignment code.
+pub const ASSIGNMENT: &str = "assignment";
+/// YUL function definition code.
+pub const FUNCTION_DEFINITION: &str = "function_definition";
+/// YUL function leave code.
+pub const LEAVE: &str = "leave";
+
+/// The dwarf dump analyzer.
+///
+/// Loads debug information from `llvm-dwarfdump` and calculates statistics
+/// about the compiled YUL statements:
+/// - Statements count
+/// - Per-statement
+#[derive(Debug, Default)]
+pub struct DwarfdumpAnalyzer {
+    /// The YUL source file path.
+    source: PathBuf,
+
+    /// The YUL location to statements map.
+    location_map: LocationMap,
+
+    /// The `llvm-dwarfdump --debug-lines` output.
+    debug_lines: String,
+
+    /// The observed statements.
+    statements_count: HashMap<String, usize>,
+    /// The observed statement to instructions size.
+    statements_size: HashMap<String, u64>,
+}
+
+impl DwarfdumpAnalyzer {
+    /// The debug info analyzer constructor.
+    ///
+    /// `source` is the path to the YUL source file.
+    /// `debug_lines` is the `llvm-dwarfdump --debug-lines` output.
+    pub fn new(source: &Path, debug_lines: String) -> Self {
+        Self {
+            source: source.to_path_buf(),
+            debug_lines,
+            ..Default::default()
+        }
+    }
+
+    /// Run the analysis.
+    pub fn analyze(&mut self) -> anyhow::Result<()> {
+        self.map_locations()?;
+        self.analyze_statements()?;
+        Ok(())
+    }
+
+    /// Populate the maps so that we can always unwrap later.
+    fn map_locations(&mut self) -> anyhow::Result<()> {
+        self.location_map = map_locations(&self.source)?;
+
+        self.statements_count = HashMap::with_capacity(self.location_map.len());
+        self.statements_size = HashMap::with_capacity(self.location_map.len());
+
+        for statement in self.location_map.values() {
+            if !self.statements_size.contains_key(statement) {
+                self.statements_size.insert(statement.clone(), 0);
+            }
+
+            *self.statements_count.entry(statement.clone()).or_insert(0) += 1;
+        }
+
+        Ok(())
+    }
+
+    /// Analyze how much bytes of insturctions each statement contributes.
+    fn analyze_statements(&mut self) -> anyhow::Result<()> {
+        let mut previous_offset = 0;
+        let mut previous_location = Location::new(0, 0);
+
+        for line in self
+            .debug_lines
+            .lines()
+            .skip_while(|line| !line.starts_with("Address"))
+            .skip(2)
+        {
+            let mut parts = line.split_whitespace();
+            let (Some(offset), Some(line), Some(column)) =
+                (parts.next(), parts.next(), parts.next())
+            else {
+                continue;
+            };
+
+            let current_offset = u64::from_str_radix(offset.trim_start_matches("0x"), 16)?;
+            let mut current_location = Location::new(line.parse()?, column.parse()?);
+
+            // TODO: A bug? Needs further investigation.
+            if current_location.line == 0 && current_location.column != 0 {
+                current_location.line = previous_location.line;
+            }
+
+            if let Some(statement) = self.location_map.get(&previous_location) {
+                let contribution = current_offset - previous_offset;
+                *self.statements_size.get_mut(statement).unwrap() += contribution;
+            }
+
+            previous_offset = current_offset;
+            previous_location = current_location;
+        }
+
+        Ok(())
+    }
+
+    /// Print the per-statement count break-down.
+    pub fn display_statement_count(&self) {
+        println!("statements count:");
+        for (statement, count) in self.statements_count.iter() {
+            println!("\t{statement} {count}");
+        }
+    }
+
+    /// Print the per-statement byte size contribution break-down.
+    pub fn display_statement_size(&self) {
+        println!("bytes per statement:");
+        for (statement, size) in self.statements_size.iter() {
+            println!("\t{statement} {size}");
+        }
+    }
+
+    /// Print the estimated `yul-phaser` cost parameters.
+    pub fn display_phaser_costs(&self, yul_phaser_scale: u64) {
+        println!("yul-phaser parameters:");
+        for (parameter, cost) in self.phaser_costs(yul_phaser_scale) {
+            println!("\t{parameter} {cost}");
+        }
+    }
+
+    /// Estimate the `yul-phaser` costs using the simplified weight function:
+    /// `Total size / toal count = cost`
+    pub fn phaser_costs(&self, yul_phaser_scale: u64) -> Vec<(String, u64)> {
+        let mut costs: HashMap<String, (usize, u64)> = HashMap::with_capacity(16);
+        for (statement, count) in self
+            .statements_count
+            .iter()
+            .filter(|(_, count)| **count > 0)
+        {
+            let size = self.statements_size.get(statement).unwrap();
+            let cost = match statement.as_str() {
+                location_mapper::FOR => "--for-loop-cost",
+                location_mapper::OTHER => continue,
+                location_mapper::INTERNAL => continue,
+                location_mapper::BLOCK => "--block-cost",
+                location_mapper::FUNCTION_CALL => "--function-call-cost",
+                location_mapper::IF => "--if-cost",
+                location_mapper::CONTINUE => "--continue-cost",
+                location_mapper::BREAK => "--break-cost",
+                location_mapper::LEAVE => "--leave-cost",
+                location_mapper::SWITCH => "--switch-cost",
+                location_mapper::DECLARATION => "--variable-declaration-cost",
+                location_mapper::ASSIGNMENT => "--assignment-cost",
+                location_mapper::FUNCTION_DEFINITION => "--function-definition-cost",
+                _ => "--expression-statement-cost",
+            };
+
+            let entry = costs.entry(cost.to_string()).or_default();
+            entry.0 += count;
+            entry.1 += size;
+        }
+
+        let costs = costs
+            .iter()
+            .map(|(cost, (count, size))| {
+                let ratio = *size / *count as u64;
+                (cost.to_string(), ratio.min(100))
+            })
+            .collect::<Vec<_>>();
+
+        let scaled_costs = scale_to(
+            costs
+                .iter()
+                .map(|(_, ratio)| *ratio)
+                .collect::<Vec<_>>()
+                .as_slice(),
+            yul_phaser_scale,
+        );
+
+        costs
+            .iter()
+            .zip(scaled_costs)
+            .map(|((cost, _), scaled_ratio)| (cost.to_string(), scaled_ratio))
+            .collect()
+    }
+}
+
+/// Given a slice of u64 values, returns a Vec<u64> where each element
+/// is linearly scaled into the closed interval [1, 10].
+fn scale_to(data: &[u64], scale_max: u64) -> Vec<u64> {
+    if data.is_empty() {
+        return Vec::new();
+    }
+
+    let mut min = data[0];
+    let mut max = data[0];
+    for &x in &data[1..] {
+        if x < min {
+            min = x;
+        }
+        if x > max {
+            max = x;
+        }
+    }
+    if max < scale_max {
+        return data.to_vec();
+    }
+
+    let range = max - min;
+    data.iter()
+        .map(|&x| {
+            if range == 0 {
+                1
+            } else {
+                1 + (x - min) * scale_max / range
+            }
+        })
+        .collect()
+}