Cranelift: add a config option for alias analysis and redundant-load elimination. (#4349)

This allows for experiments as in here [1] and also generally gives an
option to anyone who is concerned that the extra optimization may be
counterproductive or take too much time. The optimization remains
enabled by default.

[1]
https://github.com/bytecodealliance/wasmtime/pull/4163#issuecomment-1169303683

cranelift/codegen/meta/src/shared/settings.rs

@@ -31,6 +31,16 @@ pub(crate) fn define() -> SettingGroup {
         vec!["none", "speed", "speed_and_size"],
     );
 
+    settings.add_bool(
+        "enable_alias_analysis",
+        "Do redundant-load optimizations with alias analysis.",
+        r#"
+            This enables the use of a simple alias analysis to optimize away redundant loads.
+            Only effective when `opt_level` is `speed` or `speed_and_size`.
+        "#,
+        true,
+    );
+
     settings.add_bool(
         "enable_verifier",
         "Run the Cranelift IR verifier at strategic times during compilation.",