diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index d4ff741fb6..409d90ebcf 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -269,6 +269,45 @@ jobs:
       env:
         RUST_BACKTRACE: 1
 
+  # Perform all tests (debug mode) for `wasmtime` with the experimental x64
+  # backend. This runs on the nightly channel of Rust (because of issues with
+  # unifying Cargo features on stable) on Ubuntu.
+  test_x64:
+    name: Test x64 new backend
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+      with:
+        submodules: true
+    - uses: ./.github/actions/install-rust
+      with:
+        toolchain: nightly-2020-07-27
+    - uses: ./.github/actions/define-llvm-env
+
+    # 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
+
+    # Build and test all features except for lightbeam
+    - run: |
+        cargo \
+            -Zfeatures=all -Zpackage-features \
+            test \
+            --features test-programs/test_programs \
+            --features experimental_x64 \
+            --all \
+            --exclude lightbeam \
+            --exclude peepmatic \
+            --exclude peepmatic-automata \
+            --exclude peepmatic-fuzzing \
+            --exclude peepmatic-macro \
+            --exclude peepmatic-runtime \
+            --exclude peepmatic-test
+      env:
+        RUST_BACKTRACE: 1
+
+
   # Verify that cranelift's code generation is deterministic
   meta_determinist_check:
     name: Meta deterministic check
diff --git a/build.rs b/build.rs
index 753e28b80f..5698adac4a 100644
--- a/build.rs
+++ b/build.rs
@@ -151,7 +151,12 @@ fn write_testsuite_tests(
     let testname = extract_name(path);
 
     writeln!(out, "#[test]")?;
-    if ignore(testsuite, &testname, strategy) {
+    if experimental_x64_should_panic(testsuite, &testname, strategy) {
+        writeln!(
+            out,
+            r#"#[cfg_attr(feature = "experimental_x64", should_panic)]"#
+        )?;
+    } else if ignore(testsuite, &testname, strategy) {
         writeln!(out, "#[ignore]")?;
     }
     writeln!(out, "fn r#{}() {{", &testname)?;
@@ -167,6 +172,21 @@ fn write_testsuite_tests(
     Ok(())
 }
 
+/// For experimental_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" {
+        return false;
+    }
+
+    match (testsuite, testname) {
+        ("simd", _) => return true,
+        _ => {}
+    }
+
+    false
+}
+
 /// Ignore tests that aren't supported yet.
 fn ignore(testsuite: &str, testname: &str, strategy: &str) -> bool {
     let target = env::var("TARGET").unwrap();
diff --git a/cranelift/codegen/src/isa/x64/lower.rs b/cranelift/codegen/src/isa/x64/lower.rs
index 11f6e59392..0230074ffc 100644
--- a/cranelift/codegen/src/isa/x64/lower.rs
+++ b/cranelift/codegen/src/isa/x64/lower.rs
@@ -347,7 +347,7 @@ fn lower_insn_to_regs<C: LowerCtx<I = Inst>>(
     };
 
     match op {
-        Opcode::Iconst | Opcode::Null => {
+        Opcode::Iconst | Opcode::Bconst | Opcode::Null => {
             if let Some(w64) = iri_to_u64_imm(ctx, insn) {
                 let dst_is_64 = w64 > 0x7fffffff;
                 let dst = output_to_reg(ctx, outputs[0]);
diff --git a/cranelift/codegen/src/isa/x86/unwind/systemv.rs b/cranelift/codegen/src/isa/x86/unwind/systemv.rs
index ecbcbb1dd1..e292f39b95 100644
--- a/cranelift/codegen/src/isa/x86/unwind/systemv.rs
+++ b/cranelift/codegen/src/isa/x86/unwind/systemv.rs
@@ -397,6 +397,7 @@ mod tests {
     use target_lexicon::triple;
 
     #[test]
+    #[cfg_attr(feature = "x64", should_panic)] // TODO #2079
     fn test_simple_func() {
         let isa = lookup(triple!("x86_64"))
             .expect("expect x86 ISA")
@@ -439,6 +440,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg_attr(feature = "x64", should_panic)] // TODO #2079
     fn test_multi_return_func() {
         let isa = lookup(triple!("x86_64"))
             .expect("expect x86 ISA")
diff --git a/cranelift/codegen/src/isa/x86/unwind/winx64.rs b/cranelift/codegen/src/isa/x86/unwind/winx64.rs
index 79afc27643..c52112d78d 100644
--- a/cranelift/codegen/src/isa/x86/unwind/winx64.rs
+++ b/cranelift/codegen/src/isa/x86/unwind/winx64.rs
@@ -158,6 +158,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg_attr(feature = "x64", should_panic)] // TODO #2079
     fn test_small_alloc() {
         let isa = lookup(triple!("x86_64"))
             .expect("expect x86 ISA")
@@ -215,6 +216,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg_attr(feature = "x64", should_panic)] // TODO #2079
     fn test_medium_alloc() {
         let isa = lookup(triple!("x86_64"))
             .expect("expect x86 ISA")
@@ -276,6 +278,7 @@ mod tests {
     }
 
     #[test]
+    #[cfg_attr(feature = "x64", should_panic)] // TODO #2079
     fn test_large_alloc() {
         let isa = lookup(triple!("x86_64"))
             .expect("expect x86 ISA")
diff --git a/cranelift/tests/filetests.rs b/cranelift/tests/filetests.rs
index a633461109..edf6513ccf 100644
--- a/cranelift/tests/filetests.rs
+++ b/cranelift/tests/filetests.rs
@@ -1,4 +1,5 @@
 #[test]
+#[cfg_attr(feature = "experimental_x64", should_panic)] // TODO #2079
 fn filetests() {
     // Run all the filetests in the following directories.
     cranelift_filetests::run(false, false, &["filetests".into(), "docs".into()])
diff --git a/crates/wiggle/macro/Cargo.toml b/crates/wiggle/macro/Cargo.toml
index 208182a21b..af8e3e87b1 100644
--- a/crates/wiggle/macro/Cargo.toml
+++ b/crates/wiggle/macro/Cargo.toml
@@ -14,6 +14,12 @@ include = ["src/**/*", "LICENSE"]
 proc-macro = true
 test = false
 
+# This has been added to make testing of the experimental_x64 feature possible,
+# working around a Cargo nightly bug: once
+# https://github.com/rust-lang/cargo/issues/8563 has been fixed, we should be
+# able to revert it.
+doctest = false
+
 [dependencies]
 wiggle-generate = { path = "../generate", version = "0.19.0" }
 witx = { path = "../../wasi-common/WASI/tools/witx", version = "0.8.5" }
diff --git a/tests/all/gc.rs b/tests/all/gc.rs
index e616b2d0c8..005d5152da 100644
--- a/tests/all/gc.rs
+++ b/tests/all/gc.rs
@@ -373,6 +373,7 @@ fn gc_during_gc_when_passing_refs_into_wasm() -> anyhow::Result<()> {
 }
 
 #[test]
+#[cfg_attr(feature = "experimental_x64", ignore)] // TODO #2079 investigate.
 fn gc_during_gc_from_many_table_gets() -> anyhow::Result<()> {
     let (store, module) = ref_types_module(
         r#"
diff --git a/tests/all/iloop.rs b/tests/all/iloop.rs
index 23e6f85aa8..6f59800adc 100644
--- a/tests/all/iloop.rs
+++ b/tests/all/iloop.rs
@@ -99,6 +99,7 @@ fn loop_interrupt_from_afar() -> anyhow::Result<()> {
 }
 
 #[test]
+#[cfg_attr(feature = "experimental_x64", ignore)] // TODO #2079 interrupts in wasmtime
 fn function_interrupt_from_afar() -> anyhow::Result<()> {
     // Create an instance which calls an imported function on each iteration of
     // the loop so we can count the number of loop iterations we've executed so
diff --git a/tests/all/stack_overflow.rs b/tests/all/stack_overflow.rs
index 97e9dc1a08..edf557aa14 100644
--- a/tests/all/stack_overflow.rs
+++ b/tests/all/stack_overflow.rs
@@ -2,6 +2,7 @@ use std::sync::atomic::{AtomicUsize, Ordering::SeqCst};
 use wasmtime::*;
 
 #[test]
+#[cfg_attr(feature = "experimental_x64", ignore)] // TODO #2079 require probe stacks
 fn host_always_has_some_stack() -> anyhow::Result<()> {
     static HITS: AtomicUsize = AtomicUsize::new(0);
     // assume hosts always have at least 512k of stack
diff --git a/tests/all/traps.rs b/tests/all/traps.rs
index 27285b241a..c85cd98646 100644
--- a/tests/all/traps.rs
+++ b/tests/all/traps.rs
@@ -32,6 +32,7 @@ fn test_trap_return() -> Result<()> {
 
 #[test]
 #[cfg_attr(target_arch = "aarch64", ignore)] // FIXME(#1642)
+#[cfg_attr(feature = "experimental_x64", ignore)] // FIXME(#2078)
 fn test_trap_trace() -> Result<()> {
     let store = Store::default();
     let wat = r#"
@@ -74,6 +75,7 @@ fn test_trap_trace() -> Result<()> {
 
 #[test]
 #[cfg_attr(target_arch = "aarch64", ignore)] // FIXME(#1642)
+#[cfg_attr(feature = "experimental_x64", ignore)] // FIXME(#2078)
 fn test_trap_trace_cb() -> Result<()> {
     let store = Store::default();
     let wat = r#"
@@ -110,6 +112,7 @@ fn test_trap_trace_cb() -> Result<()> {
 
 #[test]
 #[cfg_attr(target_arch = "aarch64", ignore)] // FIXME(#1642)
+#[cfg_attr(feature = "experimental_x64", ignore)] // FIXME(#2078)
 fn test_trap_stack_overflow() -> Result<()> {
     let store = Store::default();
     let wat = r#"
@@ -142,6 +145,7 @@ fn test_trap_stack_overflow() -> Result<()> {
 
 #[test]
 #[cfg_attr(target_arch = "aarch64", ignore)] // FIXME(#1642)
+#[cfg_attr(feature = "experimental_x64", ignore)] // FIXME(#2078)
 fn trap_display_pretty() -> Result<()> {
     let store = Store::default();
     let wat = r#"
@@ -174,6 +178,7 @@ wasm backtrace:
 
 #[test]
 #[cfg_attr(target_arch = "aarch64", ignore)] // FIXME(#1642)
+#[cfg_attr(feature = "experimental_x64", ignore)] // FIXME(#2078)
 fn trap_display_multi_module() -> Result<()> {
     let store = Store::default();
     let wat = r#"
@@ -219,6 +224,7 @@ wasm backtrace:
 
 #[test]
 #[cfg_attr(target_arch = "aarch64", ignore)] // FIXME(#1642)
+#[cfg_attr(feature = "experimental_x64", ignore)] // FIXME(#2078)
 fn trap_start_function_import() -> Result<()> {
     let store = Store::default();
     let binary = wat::parse_str(
@@ -246,6 +252,7 @@ fn trap_start_function_import() -> Result<()> {
 
 #[test]
 #[cfg_attr(target_arch = "aarch64", ignore)] // FIXME(#1642)
+#[cfg_attr(feature = "experimental_x64", ignore)] // FIXME(#2078)
 fn rust_panic_import() -> Result<()> {
     let store = Store::default();
     let binary = wat::parse_str(
@@ -291,6 +298,7 @@ fn rust_panic_import() -> Result<()> {
 
 #[test]
 #[cfg_attr(target_arch = "aarch64", ignore)] // FIXME(#1642)
+#[cfg_attr(feature = "experimental_x64", ignore)] // FIXME(#2078)
 fn rust_panic_start_function() -> Result<()> {
     let store = Store::default();
     let binary = wat::parse_str(
@@ -325,6 +333,7 @@ fn rust_panic_start_function() -> Result<()> {
 
 #[test]
 #[cfg_attr(target_arch = "aarch64", ignore)] // FIXME(#1642)
+#[cfg_attr(feature = "experimental_x64", ignore)] // FIXME(#2078)
 fn mismatched_arguments() -> Result<()> {
     let store = Store::default();
     let binary = wat::parse_str(
@@ -357,6 +366,7 @@ fn mismatched_arguments() -> Result<()> {
 
 #[test]
 #[cfg_attr(target_arch = "aarch64", ignore)] // FIXME(#1642)
+#[cfg_attr(feature = "experimental_x64", ignore)] // FIXME(#2078)
 fn call_signature_mismatch() -> Result<()> {
     let store = Store::default();
     let binary = wat::parse_str(
@@ -388,6 +398,7 @@ fn call_signature_mismatch() -> Result<()> {
 
 #[test]
 #[cfg_attr(target_arch = "aarch64", ignore)] // FIXME(#1642)
+#[cfg_attr(feature = "experimental_x64", ignore)] // FIXME(#2078)
 fn start_trap_pretty() -> Result<()> {
     let store = Store::default();
     let wat = r#"