fuzzgen: Minimize regalloc_checker compiles

Author: afonso360

cranelift/fuzzgen/src/config.rs

@@ -1,3 +1,4 @@
+use std::collections::HashMap;
 use std::ops::RangeInclusive;
 
 /// Holds the range of acceptable values to use during the generation of testcases
@@ -54,6 +55,11 @@ pub struct Config {
     /// We insert a checking sequence to guarantee that those inputs never make
     /// it to the instruction, but sometimes we want to allow them.
     pub allowed_fcvt_traps_ratio: (usize, usize),
+
+    /// Some flags really impact compile performance, we still want to test
+    /// them, but probably at a lower rate, so that overall execution time isn't
+    /// impacted as much
+    pub compile_flag_ratio: HashMap<&'static str, (usize, usize)>,
 }
 
 impl Default for Config {
@@ -79,6 +85,7 @@ impl Default for Config {
             backwards_branch_ratio: (1, 1000),
             allowed_int_divz_ratio: (1, 1_000_000),
             allowed_fcvt_traps_ratio: (1, 1_000_000),
+            compile_flag_ratio: [("regalloc_checker", (1usize, 100))].into_iter().collect(),
         }
     }
 }

cranelift/fuzzgen/src/lib.rs

@@ -257,7 +257,14 @@ where
             "enable_llvm_abi_extensions",
         ];
         for flag_name in bool_settings {
-            let value = format!("{}", bool::arbitrary(self.u)?);
+            let enabled = self
+                .config
+                .compile_flag_ratio
+                .get(&flag_name)
+                .map(|&(num, denum)| self.u.ratio(num, denum))
+                .unwrap_or_else(|| bool::arbitrary(self.u))?;
+
+            let value = format!("{}", enabled);
             builder.set(flag_name, value.as_str())?;
         }