Switch default to new x86_64 backend.

This PR switches the default backend on x86, for both the
`cranelift-codegen` crate and for Wasmtime, to the new
(`MachInst`-style, `VCode`-based) backend that has been under
development and testing for some time now.

The old backend is still available by default in builds with the
`old-x86-backend` feature, or by requesting `BackendVariant::Legacy`
from the appropriate APIs.

As part of that switch, it adds some more runtime-configurable plumbing
to the testing infrastructure so that tests can be run using the
appropriate backend. `clif-util test` is now capable of parsing a
backend selector option from filetests and instantiating the correct
backend.

CI has been updated so that the old x86 backend continues to run its
tests, just as we used to run the new x64 backend separately.

At some point, we will remove the old x86 backend entirely, once we are
satisfied that the new backend has not caused any unforeseen issues and
we do not need to revert.

.github/workflows/main.yml

@@ -296,7 +296,7 @@ jobs:
     # Test debug (DWARF) related functionality on new backend.
     - run: |
         sudo apt-get update && sudo apt-get install -y gdb
-        cargo test --features experimental_x64 test_debug_dwarf -- --ignored --test-threads 1 --test debug::
+        cargo test test_debug_dwarf -- --ignored --test-threads 1 --test debug::
       if: matrix.os == 'ubuntu-latest'
       env:
         RUST_BACKTRACE: 1
@@ -319,12 +319,10 @@ jobs:
         RUST_BACKTRACE: 1
 
   # Perform all tests (debug mode) for `wasmtime` with the experimental x64
-  # backend. This runs on an older nightly of Rust (because of issues with
-  # unifying Cargo features on stable) on Ubuntu such that it's new enough
-  # to build Wasmtime, but old enough where the -Z options being used
-  # haven't been stabilized yet.
-  test_x64:
-    name: Test x64 new backend
+  # backend. This runs on the nightly channel of Rust (because of issues with
+  # unifying Cargo features on stable) on Ubuntu.
+  test_old_x86_backend:
+    name: Test old x86 backend
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v2
@@ -341,40 +339,7 @@ jobs:
     - run: rustup target add wasm32-unknown-unknown
 
     # Run the x64 CI script.
-    - run: ./ci/run-experimental-x64-ci.sh
-      env:
-        CARGO_VERSION: "+nightly-2020-12-26"
-        RUST_BACKTRACE: 1
-
-  # Perform tests on the new x64 backend on Windows as well.
-  test_x64_win:
-    name: Test x64 new backend on Windows
-    runs-on: windows-latest
-    steps:
-    - uses: actions/checkout@v2
-      with:
-        submodules: true
-    - uses: ./.github/actions/install-rust
-      with:
-        toolchain: nightly-2020-11-29
-    - uses: ./.github/actions/define-llvm-env
-
-    - name: Install libclang
-      # Note: libclang is pre-installed on the macOS and linux images.
-      if: matrix.os == 'windows-latest'
-      run: |
-        curl https://releases.llvm.org/9.0.0/LLVM-9.0.0-win64.exe -o llvm-installer.exe
-        7z x llvm-installer.exe -oC:/llvm-binary
-        echo LIBCLANG_PATH=C:/llvm-binary/bin/libclang.dll >> $GITHUB_ENV
-        echo C:/llvm-binary/bin >> $GITHUB_PATH
-
-    # Install wasm32 targets in order to build various tests throughout the
-    # repo.
-    - run: rustup target add wasm32-wasi
-    - run: rustup target add wasm32-unknown-unknown
-
-    # Run the x64 CI script.
-    - run: ./ci/run-experimental-x64-ci.sh
+    - run: ./ci/run-old-x86-ci.sh
       env:
         CARGO_VERSION: "+nightly-2020-11-29"
         RUST_BACKTRACE: 1

Cargo.toml

@@ -93,9 +93,8 @@ wasi-crypto = ["wasmtime-wasi-crypto"]
 wasi-nn = ["wasmtime-wasi-nn"]
 uffd = ["wasmtime/uffd"]
 
-# Try the experimental, work-in-progress new x86_64 backend. This is not stable
-# as of June 2020.
-experimental_x64 = ["wasmtime-jit/experimental_x64"]
+# Use the old x86 backend.
+old-x86-backend = ["wasmtime-jit/old-x86-backend"]
 
 [badges]
 maintenance = { status = "actively-developed" }

build.rs

@@ -155,11 +155,8 @@ fn write_testsuite_tests(
     let testname = extract_name(path);
 
     writeln!(out, "#[test]")?;
-    if experimental_x64_should_panic(testsuite, &testname, strategy) {
-        writeln!(
-            out,
-            r#"#[cfg_attr(feature = "experimental_x64", should_panic)]"#
-        )?;
+    if x64_should_panic(testsuite, &testname, strategy) {
+        writeln!(out, r#"#[should_panic]"#)?;
     } else if ignore(testsuite, &testname, strategy) {
         writeln!(out, "#[ignore]")?;
     } else if pooling {
@@ -186,10 +183,10 @@ fn write_testsuite_tests(
     Ok(())
 }
 
-/// For experimental_x64 backend features that are not supported yet, mark tests as panicking, so
+/// For x64 backend features that are not supported yet, mark tests as panicking, so
 /// they stop "passing" once the features are properly implemented.
-fn experimental_x64_should_panic(testsuite: &str, testname: &str, strategy: &str) -> bool {
-    if !cfg!(feature = "experimental_x64") || strategy != "Cranelift" {
+fn x64_should_panic(testsuite: &str, testname: &str, strategy: &str) -> bool {
+    if !platform_is_x64() || strategy != "Cranelift" {
         return false;
     }
 
@@ -222,15 +219,11 @@ fn ignore(testsuite: &str, testname: &str, strategy: &str) -> bool {
             _ => (),
         },
         "Cranelift" => match (testsuite, testname) {
-            // TODO(#1886): Ignore reference types tests if this isn't x64,
-            // because Cranelift only supports reference types on x64.
-            ("reference_types", _) => {
-                return env::var("CARGO_CFG_TARGET_ARCH").unwrap() != "x86_64";
-            }
-
+            ("simd", _) if cfg!(feature = "old-x86-backend") => return true, // skip all SIMD tests on old backend.
             // These are new instructions that are not really implemented in any backend.
             ("simd", "simd_i8x16_arith2")
             | ("simd", "simd_conversions")
+            | ("simd", "simd_boolean")
             | ("simd", "simd_i16x8_extadd_pairwise_i8x16")
             | ("simd", "simd_i16x8_extmul_i8x16")
             | ("simd", "simd_i16x8_q15mulr_sat_s")
@@ -240,26 +233,14 @@ fn ignore(testsuite: &str, testname: &str, strategy: &str) -> bool {
             | ("simd", "simd_i64x2_extmul_i32x4")
             | ("simd", "simd_int_to_int_extend") => return true,
 
-            // These are only implemented on x64.
-            ("simd", "simd_i64x2_arith2") | ("simd", "simd_boolean") => {
-                return !cfg!(feature = "experimental_x64")
-            }
-
-            // These are only implemented on aarch64 and x64.
-            ("simd", "simd_i64x2_cmp")
-            | ("simd", "simd_f32x4_pmin_pmax")
-            | ("simd", "simd_f64x2_pmin_pmax")
-            | ("simd", "simd_f32x4_rounding")
-            | ("simd", "simd_f64x2_rounding")
-            | ("simd", "simd_i32x4_dot_i16x8") => {
-                return !(cfg!(feature = "experimental_x64")
-                    || env::var("CARGO_CFG_TARGET_ARCH").unwrap() == "aarch64")
-            }
-
             _ => {}
         },
         _ => panic!("unrecognized strategy"),
     }
 
     false
 }
+
+fn platform_is_x64() -> bool {
+    env::var("CARGO_CFG_TARGET_ARCH").unwrap() == "x86_64"
+}

ci/run-experimental-x64-ci.sh → ci/run-old-x86-ci.sh

@@ -1,7 +1,7 @@
 #!/bin/bash
 
 # Use the Nightly variant of the compiler to properly unify the
-# experimental_x64 feature across all crates.  Once the feature has stabilized
+# across all crates.  Once the feature has stabilized
 # and become the default, we can remove this.
 CARGO_VERSION=${CARGO_VERSION:-"+nightly"}
 
@@ -20,7 +20,7 @@ cargo $CARGO_VERSION \
             -Zfeatures=all -Zpackage-features \
             test \
             --features test-programs/test_programs \
-            --features experimental_x64 \
+            --features old-x86-backend \
             --all \
             --exclude wasmtime-lightbeam \
             --exclude wasmtime-wasi-nn \

cranelift/Cargo.toml

@@ -50,6 +50,5 @@ default = ["disas", "wasm", "cranelift-codegen/all-arch", "peepmatic-souper", "s
 disas = ["capstone"]
 enable-peepmatic = ["cranelift-codegen/enable-peepmatic", "cranelift-filetests/enable-peepmatic"]
 wasm = ["wat", "cranelift-wasm"]
-experimental_x64 = ["cranelift-codegen/x64", "cranelift-filetests/experimental_x64", "cranelift-reader/experimental_x64"]
 experimental_arm32 = ["cranelift-codegen/arm32", "cranelift-filetests/experimental_arm32"]
 souper-harvest = ["cranelift-codegen/souper-harvest", "rayon"]

cranelift/codegen/Cargo.toml

@@ -63,9 +63,11 @@ unwind = ["gimli"]
 x86 = []
 arm64 = []
 riscv = []
-x64 = [] # New work-in-progress codegen backend for x86_64 based on the new isel.
 arm32 = [] # Work-in-progress codegen backend for ARM.
 
+# Make the old x86 backend the default.
+old-x86-backend = []
+
 # Option to enable all architectures.
 all-arch = [
     "x86",

cranelift/codegen/src/isa/mod.rs

@@ -75,16 +75,15 @@ use thiserror::Error;
 #[cfg(feature = "riscv")]
 mod riscv;
 
-// N.B.: the old x86-64 backend (`x86`) and the new one (`x64`) can both be
-// included; if the new backend is included, then it is the default backend
-// returned for an x86-64 triple, but a specific option can request the old
-// backend. It is important to have the ability to instantiate *both* backends
-// in the same build so that we can do things like differential fuzzing between
-// backends, or perhaps offer a runtime configuration flag in the future.
+// N.B.: the old x86-64 backend (`x86`) and the new one (`x64`) are both
+// included whenever building with x86 support. The new backend is the default,
+// but the old can be requested with `BackendVariant::Legacy`. However, if this
+// crate is built with the `old-x86-backend` feature, then the old backend is
+// default instead.
 #[cfg(feature = "x86")]
 mod x86;
 
-#[cfg(feature = "x64")]
+#[cfg(feature = "x86")]
 mod x64;
 
 #[cfg(feature = "arm32")]
@@ -123,7 +122,7 @@ macro_rules! isa_builder {
 /// The "variant" for a given target. On one platform (x86-64), we have two
 /// backends, the "old" and "new" one; the new one is the default if included
 /// in the build configuration and not otherwise specified.
-#[derive(Clone, Copy)]
+#[derive(Clone, Copy, Debug)]
 pub enum BackendVariant {
     /// Any backend available.
     Any,
@@ -150,13 +149,13 @@ pub fn lookup_variant(triple: Triple, variant: BackendVariant) -> Result<Builder
             isa_builder!(x86, (feature = "x86"), triple)
         }
         (Architecture::X86_64, BackendVariant::MachInst) => {
-            isa_builder!(x64, (feature = "x64"), triple)
+            isa_builder!(x64, (feature = "x86"), triple)
         }
-        #[cfg(feature = "x64")]
+        #[cfg(not(feature = "old-x86-backend"))]
         (Architecture::X86_64, BackendVariant::Any) => {
-            isa_builder!(x64, (feature = "x64"), triple)
+            isa_builder!(x64, (feature = "x86"), triple)
         }
-        #[cfg(not(feature = "x64"))]
+        #[cfg(feature = "old-x86-backend")]
         (Architecture::X86_64, BackendVariant::Any) => {
             isa_builder!(x86, (feature = "x86"), triple)
         }
@@ -265,6 +264,11 @@ pub trait TargetIsa: fmt::Display + Send + Sync {
     /// Get the ISA-independent flags that were used to make this trait object.
     fn flags(&self) -> &settings::Flags;
 
+    /// Get the variant of this ISA (Legacy or MachInst).
+    fn variant(&self) -> BackendVariant {
+        BackendVariant::Legacy
+    }
+
     /// Hashes all flags, both ISA-independent and ISA-specific, into the
     /// specified hasher.
     fn hash_all_flags(&self, hasher: &mut dyn Hasher);

cranelift/codegen/src/isa/x64/inst/args.rs

@@ -1,3 +1,5 @@
+#![allow(dead_code)]
+
 //! Instruction operand sub-components (aka "parts"): definitions and printing.
 
 use super::regs::{self, show_ireg_sized};

cranelift/codegen/src/isa/x64/inst/unwind/systemv.rs

@@ -109,6 +109,7 @@ mod tests {
     use target_lexicon::triple;
 
     #[test]
+    #[cfg_attr(feature = "old-x86-backend", ignore)]
     fn test_simple_func() {
         let isa = lookup(triple!("x86_64"))
             .expect("expect x86 ISA")
@@ -151,6 +152,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg_attr(feature = "old-x86-backend", ignore)]
     fn test_multi_return_func() {
         let isa = lookup(triple!("x86_64"))
             .expect("expect x86 ISA")

cranelift/codegen/src/isa/x64/lower.rs

@@ -199,6 +199,7 @@ fn input_to_reg_mem<C: LowerCtx<I = Inst>>(ctx: &mut C, spec: InsnInput) -> RegM
 }
 
 /// An extension specification for `extend_input_to_reg`.
+#[allow(dead_code)]
 #[derive(Clone, Copy)]
 enum ExtSpec {
     ZeroExtendTo32,

cranelift/codegen/src/machinst/adapter.rs

@@ -2,7 +2,9 @@
 
 use crate::binemit;
 use crate::ir;
-use crate::isa::{EncInfo, Encoding, Encodings, Legalize, RegClass, RegInfo, TargetIsa};
+use crate::isa::{
+    BackendVariant, EncInfo, Encoding, Encodings, Legalize, RegClass, RegInfo, TargetIsa,
+};
 use crate::machinst::*;
 use crate::regalloc::RegisterSet;
 use crate::settings::Flags;
@@ -59,6 +61,10 @@ impl TargetIsa for TargetIsaAdapter {
         self.backend.flags()
     }
 
+    fn variant(&self) -> BackendVariant {
+        BackendVariant::MachInst
+    }
+
     fn hash_all_flags(&self, hasher: &mut dyn Hasher) {
         self.backend.hash_all_flags(hasher)
     }

cranelift/filetests/Cargo.toml

@@ -30,4 +30,3 @@ anyhow = "1.0.32"
 [features]
 enable-peepmatic = []
 experimental_arm32 = []
-experimental_x64 = []

cranelift/filetests/filetests/isa/x64/amode-opt.clif

@@ -1,7 +1,6 @@
 test compile
 set unwind_info=false
-target x86_64
-feature "experimental_x64"
+target x86_64 machinst
 
 function %amode_add(i64, i64) -> i64 {
 block0(v0: i64, v1: i64):

cranelift/filetests/filetests/isa/x64/b1.clif

@@ -1,7 +1,6 @@
 test compile
 set unwind_info=false
-target x86_64
-feature "experimental_x64"
+target x86_64 machinst
 
 function %f0(b1, i32, i32) -> i32 {
 ; check:  pushq   %rbp

cranelift/filetests/filetests/isa/x64/basic.clif

@@ -1,7 +1,6 @@
 test compile
 set unwind_info=false
-target x86_64
-feature "experimental_x64"
+target x86_64 machinst
 
 function %f(i32, i32) -> i32 {
 block0(v0: i32, v1: i32):

cranelift/filetests/filetests/isa/x64/bitops-i128-run.clif

@@ -1,6 +1,5 @@
 test run
-target x86_64
-feature "experimental_x64"
+target x86_64 machinst
 
 function %ctz(i64, i64) -> i8 {
 block0(v0: i64, v1: i64):

cranelift/filetests/filetests/isa/x64/bitrev-i128-run.clif

@@ -1,6 +1,5 @@
 test run
-target x86_64
-feature "experimental_x64"
+target x86_64 machinst
 
 function %reverse_bits_zero() -> b1 {
 block0:

cranelift/filetests/filetests/isa/x64/branches.clif

@@ -1,7 +1,6 @@
 test compile
 set unwind_info=false
-target x86_64
-feature "experimental_x64"
+target x86_64 machinst
 
 function %f0(i32, i32) -> i32 {
 block0(v0: i32, v1: i32):

cranelift/filetests/filetests/isa/x64/clz-lzcnt.clif

@@ -1,7 +1,6 @@
 test compile
 set unwind_info=false
-target x86_64 has_lzcnt
-feature "experimental_x64"
+target x86_64 machinst has_lzcnt
 
 function %clz(i64) -> i64 {
 block0(v0: i64):

cranelift/filetests/filetests/isa/x64/cmp-mem-bug.clif

@@ -1,7 +1,6 @@
 test compile
 set unwind_info=false
-target x86_64
-feature "experimental_x64"
+target x86_64 machinst
 
 function %f0(i64, i64) -> i64, i64 {
 block0(v0: i64, v1: i64):

cranelift/filetests/filetests/isa/x64/ctz-bmi1.clif

@@ -1,7 +1,6 @@
 test compile
 set unwind_info=false
-target x86_64 has_bmi1
-feature "experimental_x64"
+target x86_64 machinst has_bmi1
 
 function %ctz(i64) -> i64 {
 block0(v0: i64):