Add an enable_verifier setting.

This is off by default, but enabled by the parser when reading a textual
IL file. Test files can still override the default to turn off
verification.

The setting enables IL verifier passes at critical points of the
compilation pipeline.

lib/cretonne/meta/base/settings.py

@@ -18,6 +18,14 @@ opt_level = EnumSetting(
         """,
         'default', 'best', 'fastest')
 
+enable_verifier = BoolSetting(
+        """
+        Run the Cretonne IL verifier at strategic times during compilation.
+
+        This makes compilation slower but catches many bugs. The verifier is
+        disabled by default, except when reading Cretonne IL from a text file.
+        """)
+
 is_64bit = BoolSetting("Enable 64-bit code generation")
 
 is_compressed = BoolSetting("Enable compressed instructions")

lib/cretonne/src/settings.rs

@@ -271,6 +271,7 @@ mod tests {
         assert_eq!(f.to_string(),
                    "[shared]\n\
                     opt_level = \"default\"\n\
+                    enable_verifier = false\n\
                     is_64bit = false\n\
                     is_compressed = false\n\
                     enable_float = true\n\

lib/reader/src/parser.rs

@@ -17,7 +17,7 @@ use cretonne::ir::immediates::{Imm64, Offset32, Uoffset32, Ieee32, Ieee64};
 use cretonne::ir::entities::AnyEntity;
 use cretonne::ir::instructions::{InstructionFormat, InstructionData, VariableArgs};
 use cretonne::isa::{self, TargetIsa, Encoding};
-use cretonne::settings;
+use cretonne::settings::{self, Configurable};
 use testfile::{TestFile, Details, Comment};
 use error::{Location, Error, Result};
 use lexer::{self, Lexer, Token};
@@ -577,6 +577,13 @@ impl<'a> Parser<'a> {
         let mut isas = Vec::new();
         let mut flag_builder = settings::builder();
 
+        // Change the default for `enable_verifier` to `true`. It defaults to `false` because it
+        // would slow down normal compilation, but when we're reading IL from a text file we're
+        // either testing or debugging Cretonne, and verification makes sense.
+        flag_builder
+            .set_bool("enable_verifier", true)
+            .expect("Missing enable_verifier setting");
+
         while let Some(Token::Identifier(command)) = self.token() {
             match command {
                 "set" => {
@@ -1849,7 +1856,10 @@ mod tests {
         assert_eq!(tf.commands[0].command, "cfg");
         assert_eq!(tf.commands[1].command, "verify");
         match tf.isa_spec {
-            IsaSpec::None(s) => assert!(!s.enable_float()),
+            IsaSpec::None(s) => {
+                assert!(s.enable_verifier());
+                assert!(!s.enable_float());
+            }
             _ => panic!("unexpected ISAs"),
         }
         assert_eq!(tf.preamble_comments.len(), 2);