Cranellift: remove Baldrdash support and related features.

As noted in Mozilla's bugzilla bug 1781425 [1], the SpiderMonkey team has recently determined that their current form of integration with Cranelift is too hard to maintain, and they have chosen to remove it from their codebase. If and when they decide to build updated support for Cranelift, they will adopt different approaches to several details of the integration. In the meantime, after discussion with the SpiderMonkey folks, they agree that it makes sense to remove the bits of Cranelift that exist to support the integration ("Baldrdash"), as they will not need them. Many of these bits are difficult-to-maintain special cases that are not actually tested in Cranelift proper: for example, the Baldrdash integration required Cranelift to emit function bodies without prologues/epilogues, and instead communicate very precise information about the expected frame size and layout, then stitched together something post-facto. This was brittle and caused a lot of incidental complexity ("fallthrough returns", the resulting special logic in block-ordering); this is just one example. As another example, one particular Baldrdash ABI variant processed stack args in reverse order, so our ABI code had to support both traversal orders. We had a number of other Baldrdash-specific settings as well that did various special things. This PR removes Baldrdash ABI support, the `fallthrough_return` instruction, and pulls some threads to remove now-unused bits as a result of those two, with the understanding that the SpiderMonkey folks will build new functionality as needed in the future and we can perhaps find cleaner abstractions to make it all work. [1] https://bugzilla.mozilla.org/show_bug.cgi?id=1781425
bytecodealliance · Aug 1, 2022 · 14407fc · 14407fc
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diff --git a/cranelift/README.md b/cranelift/README.md
@@ -97,10 +97,6 @@ Cranelift is designed to be a code generator for WebAssembly, but it is
 general enough to be useful elsewhere too. The initial planned uses that
 affected its design are:
 
- - [WebAssembly compiler for the SpiderMonkey engine in
-    Firefox](spidermonkey.md#phase-1-webassembly).
- - [Backend for the IonMonkey JavaScript JIT compiler in
-    Firefox](spidermonkey.md#phase-2-ionmonkey).
  - [Debug build backend for the Rust compiler](rustc.md).
  - [Wasmtime non-Web wasm engine](https://github.com/bytecodealliance/wasmtime).
 

diff --git a/cranelift/codegen/meta/src/isa/x86.rs b/cranelift/codegen/meta/src/isa/x86.rs
@@ -170,17 +170,8 @@ fn define_settings(shared: &SettingGroup) -> SettingGroup {
     // back in the shared SettingGroup, and use it in x86 instruction predicates.
 
     let is_pic = shared.get_bool("is_pic");
-    let emit_all_ones_funcaddrs = shared.get_bool("emit_all_ones_funcaddrs");
     settings.add_predicate("is_pic", predicate!(is_pic));
     settings.add_predicate("not_is_pic", predicate!(!is_pic));
-    settings.add_predicate(
-        "all_ones_funcaddrs_and_not_is_pic",
-        predicate!(emit_all_ones_funcaddrs && !is_pic),
-    );
-    settings.add_predicate(
-        "not_all_ones_funcaddrs_and_not_is_pic",
-        predicate!(!emit_all_ones_funcaddrs && !is_pic),
-    );
 
     // Presets corresponding to x86 CPUs.
 

diff --git a/cranelift/codegen/meta/src/shared/instructions.rs b/cranelift/codegen/meta/src/shared/instructions.rs
@@ -332,24 +332,6 @@ fn define_control_flow(
         .is_terminator(true),
     );
 
-    let rvals = &Operand::new("rvals", &entities.varargs).with_doc("return values");
-    ig.push(
-        Inst::new(
-            "fallthrough_return",
-            r#"
-        Return from the function by fallthrough.
-
-        This is a specialized instruction for use where one wants to append
-        a custom epilogue, which will then perform the real return. This
-        instruction has no encoding.
-        "#,
-            &formats.multiary,
-        )
-        .operands_in(vec![rvals])
-        .is_return(true)
-        .is_terminator(true),
-    );
-
     let FN = &Operand::new("FN", &entities.func_ref)
         .with_doc("function to call, declared by `function`");
     let args = &Operand::new("args", &entities.varargs).with_doc("call arguments");

diff --git a/cranelift/codegen/meta/src/shared/settings.rs b/cranelift/codegen/meta/src/shared/settings.rs
@@ -88,8 +88,8 @@ pub(crate) fn define() -> SettingGroup {
         "avoid_div_traps",
         "Generate explicit checks around native division instructions to avoid their trapping.",
         r#"
-            This is primarily used by SpiderMonkey which doesn't install a signal
-            handler for SIGFPE, but expects a SIGILL trap for division by zero.
+            Generate explicit checks around native division instructions to
+            avoid their trapping.
 
             On ISAs like ARM where the native division instructions don't trap,
             this setting has no effect - explicit checks are always inserted.
@@ -175,8 +175,6 @@ pub(crate) fn define() -> SettingGroup {
         vec!["none", "elf_gd", "macho", "coff"],
     );
 
-    // Settings specific to the `baldrdash` calling convention.
-
     settings.add_enum(
         "libcall_call_conv",
         "Defines the calling convention to use for LibCalls call expansion.",
@@ -196,29 +194,10 @@ pub(crate) fn define() -> SettingGroup {
             "system_v",
             "windows_fastcall",
             "apple_aarch64",
-            "baldrdash_system_v",
-            "baldrdash_windows",
-            "baldrdash_2020",
             "probestack",
         ],
     );
 
-    settings.add_num(
-        "baldrdash_prologue_words",
-        "Number of pointer-sized words pushed by the baldrdash prologue.",
-        r#"
-            Functions with the `baldrdash` calling convention don't generate their
-            own prologue and epilogue. They depend on externally generated code
-            that pushes a fixed number of words in the prologue and restores them
-            in the epilogue.
-
-            This setting configures the number of pointer-sized words pushed on the
-            stack when the Cranelift-generated code is entered. This includes the
-            pushed return address on x86.
-        "#,
-        0,
-    );
-
     settings.add_bool(
         "enable_llvm_abi_extensions",
         "Enable various ABI extensions defined by LLVM's behavior.",
@@ -277,15 +256,6 @@ pub(crate) fn define() -> SettingGroup {
         false,
     );
 
-    // BaldrMonkey requires that not-yet-relocated function addresses be encoded
-    // as all-ones bitpatterns.
-    settings.add_bool(
-        "emit_all_ones_funcaddrs",
-        "Emit not-yet-relocated function addresses as all-ones bit patterns.",
-        "",
-        false,
-    );
-
     // Stack probing options.
 
     settings.add_bool(

diff --git a/cranelift/codegen/src/ir/extfunc.rs b/cranelift/codegen/src/ir/extfunc.rs
@@ -215,11 +215,6 @@ impl fmt::Display for AbiParam {
 /// particulars of the target's ABI, and the CLIF should be platform-independent, these attributes
 /// specify *how* to extend (according to the signedness of the original program) rather than
 /// *whether* to extend.
-///
-/// For example, on x86-64, the SystemV ABI does not require extensions of narrow values, so these
-/// `ArgumentExtension` attributes are ignored; but in the Baldrdash (SpiderMonkey) ABI on the same
-/// platform, all narrow values *are* extended, so these attributes may lead to extra
-/// zero/sign-extend instructions in the generated machine code.
 #[derive(Copy, Clone, PartialEq, Eq, Debug, Hash)]
 #[cfg_attr(feature = "enable-serde", derive(Serialize, Deserialize))]
 pub enum ArgumentExtension {
@@ -297,20 +292,6 @@ pub enum ArgumentPurpose {
     /// This is a pointer to a stack limit. It is used to check the current stack pointer
     /// against. Can only appear once in a signature.
     StackLimit,
-
-    /// A callee TLS value.
-    ///
-    /// In the Baldrdash-2020 calling convention, the stack upon entry to the callee contains the
-    /// TLS-register values for the caller and the callee. This argument is used to provide the
-    /// value for the callee.
-    CalleeTLS,
-
-    /// A caller TLS value.
-    ///
-    /// In the Baldrdash-2020 calling convention, the stack upon entry to the callee contains the
-    /// TLS-register values for the caller and the callee. This argument is used to provide the
-    /// value for the caller.
-    CallerTLS,
 }
 
 impl fmt::Display for ArgumentPurpose {
@@ -325,8 +306,6 @@ impl fmt::Display for ArgumentPurpose {
             Self::VMContext => "vmctx",
             Self::SignatureId => "sigid",
             Self::StackLimit => "stack_limit",
-            Self::CalleeTLS => "callee_tls",
-            Self::CallerTLS => "caller_tls",
         })
     }
 }
@@ -405,7 +384,7 @@ impl ExtFuncData {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::ir::types::{B8, F32, I32};
+    use crate::ir::types::I32;
     use alloc::string::ToString;
 
     #[test]
@@ -447,28 +426,8 @@ mod tests {
             CallConv::Cold,
             CallConv::SystemV,
             CallConv::WindowsFastcall,
-            CallConv::BaldrdashSystemV,
-            CallConv::BaldrdashWindows,
-            CallConv::Baldrdash2020,
         ] {
             assert_eq!(Ok(cc), cc.to_string().parse())
         }
     }
-
-    #[test]
-    fn signatures() {
-        let mut sig = Signature::new(CallConv::BaldrdashSystemV);
-        assert_eq!(sig.to_string(), "() baldrdash_system_v");
-        sig.params.push(AbiParam::new(I32));
-        assert_eq!(sig.to_string(), "(i32) baldrdash_system_v");
-        sig.returns.push(AbiParam::new(F32));
-        assert_eq!(sig.to_string(), "(i32) -> f32 baldrdash_system_v");
-        sig.params.push(AbiParam::new(I32.by(4).unwrap()));
-        assert_eq!(sig.to_string(), "(i32, i32x4) -> f32 baldrdash_system_v");
-        sig.returns.push(AbiParam::new(B8));
-        assert_eq!(
-            sig.to_string(),
-            "(i32, i32x4) -> f32, b8 baldrdash_system_v"
-        );
-    }
 }