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/src/context.rs

@@ -163,7 +163,7 @@ impl Context {
 
         self.remove_constant_phis(isa)?;
 
-        if opt_level != OptLevel::None {
+        if opt_level != OptLevel::None && isa.flags().enable_alias_analysis() {
             self.replace_redundant_loads()?;
             self.simple_gvn(isa)?;
         }

cranelift/codegen/src/settings.rs

@@ -516,6 +516,7 @@ libcall_call_conv = "isa_default"
 baldrdash_prologue_words = 0
 probestack_size_log2 = 12
 regalloc_checker = false
+enable_alias_analysis = true
 enable_verifier = true
 is_pic = false
 use_colocated_libcalls = false