Add a feature flag to switch between oldbe and newbe

Author: bjorn3

Cargo.toml

@@ -9,7 +9,7 @@ crate-type = ["dylib"]
 
 [dependencies]
 # These have to be in sync with each other
-cranelift-codegen = { git = "https://github.com/bytecodealliance/wasmtime/", branch = "main", features = ["unwind"] }
+cranelift-codegen = { git = "https://github.com/bytecodealliance/wasmtime/", branch = "main", features = ["unwind", "x86", "x64"] }
 cranelift-frontend = { git = "https://github.com/bytecodealliance/wasmtime/", branch = "main" }
 cranelift-module = { git = "https://github.com/bytecodealliance/wasmtime/", branch = "main" }
 cranelift-jit = { git = "https://github.com/bytecodealliance/wasmtime/", branch = "main", optional = true }
@@ -37,6 +37,7 @@ libloading = { version = "0.6.0", optional = true }
 default = ["jit", "inline_asm"]
 jit = ["cranelift-jit", "libloading"]
 inline_asm = []
+newbe = []
 
 [profile.dev]
 # By compiling dependencies with optimizations, performing tests gets much faster.

build.sh

@@ -5,6 +5,7 @@ set -e
 export CHANNEL="release"
 build_sysroot=1
 target_dir='build'
+newbe=''
 while [[ $# != 0 ]]; do
     case $1 in
         "--debug")
@@ -17,9 +18,12 @@ while [[ $# != 0 ]]; do
             target_dir=$2
             shift
             ;;
+        "--newbe")
+            newbe='--features newbe'
+            ;;
         *)
             echo "Unknown flag '$1'"
-            echo "Usage: ./build.sh [--debug] [--without-sysroot] [--target-dir DIR]"
+            echo "Usage: ./build.sh [--debug] [--without-sysroot] [--target-dir DIR] [--newbe]"
             ;;
     esac
     shift
@@ -39,9 +43,9 @@ else
    exit 1
 fi
 if [[ "$CHANNEL" == "release" ]]; then
-    cargo build --release
+    cargo build $newbe --release
 else
-    cargo build
+    cargo build $newbe
 fi
 
 rm -rf "$target_dir"

src/lib.rs

@@ -339,7 +339,12 @@ fn build_isa(sess: &Session) -> Box<dyn isa::TargetIsa + 'static> {
 
     let flags = settings::Flags::new(flags_builder);
 
-    let mut isa_builder = cranelift_codegen::isa::lookup(target_triple).unwrap();
+    let variant = if cfg!(feature = "newbe") {
+        cranelift_codegen::isa::BackendVariant::MachInst
+    } else {
+        cranelift_codegen::isa::BackendVariant::Legacy
+    };
+    let mut isa_builder = cranelift_codegen::isa::lookup_variant(target_triple, variant).unwrap();
     // Don't use "haswell", as it implies `has_lzcnt`.macOS CI is still at Ivy Bridge EP, so `lzcnt`
     // is interpreted as `bsr`.
     isa_builder.enable("nehalem").unwrap();