Rollup merge of rust-lang#134932 - RalfJung:arm-float-abi, r=workingj…

…ubilee

explicitly set float ABI for all ARM targets

We currently always set the `FloatABIType` field in the LLVM target machine to `Default`, which means LLVM infers the ARM float ABI (hard vs soft) from the LLVM target triple. This causes problems such as having to set the LLVM triple to `*-gnueabi` for our `musleabi` targets to ensure they get correctly inferred as soft-float targets. It also means rustc doesn't really know which float ABI ends up being used, which is a blocker for rust-lang#134794. So I think we should stop doing that and instead explicitly control that value. That's what this PR implements.

See [Zulip](https://rust-lang.zulipchat.com/#narrow/channel/187780-t-compiler.2Fwg-llvm/topic/Softfloat.20ABI.2C.20hardfloat.20instructions) for more context.

Best reviewed commit-by-commit. I hope I got all those `llvm_floatabi` values right...

compiler/rustc_codegen_llvm/src/back/owned_target_machine.rs

@@ -25,7 +25,7 @@ impl OwnedTargetMachine {
         model: llvm::CodeModel,
         reloc: llvm::RelocModel,
         level: llvm::CodeGenOptLevel,
-        use_soft_fp: bool,
+        float_abi: llvm::FloatAbi,
         function_sections: bool,
         data_sections: bool,
         unique_section_names: bool,
@@ -57,7 +57,7 @@ impl OwnedTargetMachine {
                 model,
                 reloc,
                 level,
-                use_soft_fp,
+                float_abi,
                 function_sections,
                 data_sections,
                 unique_section_names,

compiler/rustc_codegen_llvm/src/back/write.rs

@@ -26,7 +26,7 @@ use rustc_session::config::{
     self, Lto, OutputType, Passes, RemapPathScopeComponents, SplitDwarfKind, SwitchWithOptPath,
 };
 use rustc_span::{BytePos, InnerSpan, Pos, SpanData, SyntaxContext, sym};
-use rustc_target::spec::{CodeModel, RelocModel, SanitizerSet, SplitDebuginfo, TlsModel};
+use rustc_target::spec::{CodeModel, FloatAbi, RelocModel, SanitizerSet, SplitDebuginfo, TlsModel};
 use tracing::debug;
 
 use crate::back::lto::ThinBuffer;
@@ -181,6 +181,14 @@ pub(crate) fn to_llvm_code_model(code_model: Option<CodeModel>) -> llvm::CodeMod
     }
 }
 
+fn to_llvm_float_abi(float_abi: Option<FloatAbi>) -> llvm::FloatAbi {
+    match float_abi {
+        None => llvm::FloatAbi::Default,
+        Some(FloatAbi::Soft) => llvm::FloatAbi::Soft,
+        Some(FloatAbi::Hard) => llvm::FloatAbi::Hard,
+    }
+}
+
 pub(crate) fn target_machine_factory(
     sess: &Session,
     optlvl: config::OptLevel,
@@ -189,12 +197,12 @@ pub(crate) fn target_machine_factory(
     let reloc_model = to_llvm_relocation_model(sess.relocation_model());
 
     let (opt_level, _) = to_llvm_opt_settings(optlvl);
-    let use_softfp = if sess.target.arch == "arm" {
-        sess.opts.cg.soft_float
+    let float_abi = if sess.target.arch == "arm" && sess.opts.cg.soft_float {
+        llvm::FloatAbi::Soft
     } else {
         // `validate_commandline_args_with_session_available` has already warned about this being
         // ignored. Let's make sure LLVM doesn't suddenly start using this flag on more targets.
-        false
+        to_llvm_float_abi(sess.target.llvm_floatabi)
     };
 
     let ffunction_sections =
@@ -290,7 +298,7 @@ pub(crate) fn target_machine_factory(
             code_model,
             reloc_model,
             opt_level,
-            use_softfp,
+            float_abi,
             ffunction_sections,
             fdata_sections,
             funique_section_names,

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -526,7 +526,7 @@ pub struct SanitizerOptions {
     pub sanitize_kernel_address_recover: bool,
 }
 
-/// LLVMRelocMode
+/// LLVMRustRelocModel
 #[derive(Copy, Clone, PartialEq)]
 #[repr(C)]
 pub enum RelocModel {
@@ -538,6 +538,15 @@ pub enum RelocModel {
     ROPI_RWPI,
 }
 
+/// LLVMRustFloatABI
+#[derive(Copy, Clone, PartialEq)]
+#[repr(C)]
+pub enum FloatAbi {
+    Default,
+    Soft,
+    Hard,
+}
+
 /// LLVMRustCodeModel
 #[derive(Copy, Clone)]
 #[repr(C)]
@@ -2192,7 +2201,7 @@ unsafe extern "C" {
         Model: CodeModel,
         Reloc: RelocModel,
         Level: CodeGenOptLevel,
-        UseSoftFP: bool,
+        FloatABIType: FloatAbi,
         FunctionSections: bool,
         DataSections: bool,
         UniqueSectionNames: bool,

compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp

@@ -308,6 +308,24 @@ static Reloc::Model fromRust(LLVMRustRelocModel RustReloc) {
   report_fatal_error("Bad RelocModel.");
 }
 
+enum class LLVMRustFloatABI {
+  Default,
+  Soft,
+  Hard,
+};
+
+static FloatABI::ABIType fromRust(LLVMRustFloatABI RustFloatAbi) {
+  switch (RustFloatAbi) {
+  case LLVMRustFloatABI::Default:
+    return FloatABI::Default;
+  case LLVMRustFloatABI::Soft:
+    return FloatABI::Soft;
+  case LLVMRustFloatABI::Hard:
+    return FloatABI::Hard;
+  }
+  report_fatal_error("Bad FloatABI.");
+}
+
 /// getLongestEntryLength - Return the length of the longest entry in the table.
 template <typename KV> static size_t getLongestEntryLength(ArrayRef<KV> Table) {
   size_t MaxLen = 0;
@@ -358,7 +376,7 @@ extern "C" const char *LLVMRustGetHostCPUName(size_t *OutLen) {
 extern "C" LLVMTargetMachineRef LLVMRustCreateTargetMachine(
     const char *TripleStr, const char *CPU, const char *Feature,
     const char *ABIStr, LLVMRustCodeModel RustCM, LLVMRustRelocModel RustReloc,
-    LLVMRustCodeGenOptLevel RustOptLevel, bool UseSoftFloat,
+    LLVMRustCodeGenOptLevel RustOptLevel, LLVMRustFloatABI RustFloatABIType,
     bool FunctionSections, bool DataSections, bool UniqueSectionNames,
     bool TrapUnreachable, bool Singlethread, bool VerboseAsm,
     bool EmitStackSizeSection, bool RelaxELFRelocations, bool UseInitArray,
@@ -369,6 +387,7 @@ extern "C" LLVMTargetMachineRef LLVMRustCreateTargetMachine(
   auto OptLevel = fromRust(RustOptLevel);
   auto RM = fromRust(RustReloc);
   auto CM = fromRust(RustCM);
+  auto FloatABIType = fromRust(RustFloatABIType);
 
   std::string Error;
   auto Trip = Triple(Triple::normalize(TripleStr));
@@ -381,10 +400,7 @@ extern "C" LLVMTargetMachineRef LLVMRustCreateTargetMachine(
 
   TargetOptions Options = codegen::InitTargetOptionsFromCodeGenFlags(Trip);
 
-  Options.FloatABIType = FloatABI::Default;
-  if (UseSoftFloat) {
-    Options.FloatABIType = FloatABI::Soft;
-  }
+  Options.FloatABIType = FloatABIType;
   Options.DataSections = DataSections;
   Options.FunctionSections = FunctionSections;
   Options.UniqueSectionNames = UniqueSectionNames;

compiler/rustc_target/src/spec/base/apple/mod.rs

@@ -2,8 +2,8 @@ use std::borrow::Cow;
 use std::env;
 
 use crate::spec::{
-    Cc, DebuginfoKind, FramePointer, LinkerFlavor, Lld, SplitDebuginfo, StackProbeType, StaticCow,
-    TargetOptions, cvs,
+    Cc, DebuginfoKind, FloatAbi, FramePointer, LinkerFlavor, Lld, SplitDebuginfo, StackProbeType,
+    StaticCow, TargetOptions, cvs,
 };
 
 #[cfg(test)]
@@ -105,6 +105,7 @@ pub(crate) fn base(
 ) -> (TargetOptions, StaticCow<str>, StaticCow<str>) {
     let opts = TargetOptions {
         abi: abi.target_abi().into(),
+        llvm_floatabi: Some(FloatAbi::Hard),
         os: os.into(),
         cpu: arch.target_cpu(abi).into(),
         link_env_remove: link_env_remove(os),

compiler/rustc_target/src/spec/json.rs

@@ -116,6 +116,18 @@ impl Target {
                     Some(Ok(()))
                 })).unwrap_or(Ok(()))
             } );
+            ($key_name:ident, FloatAbi) => ( {
+                let name = (stringify!($key_name)).replace("_", "-");
+                obj.remove(&name).and_then(|o| o.as_str().and_then(|s| {
+                    match s.parse::<super::FloatAbi>() {
+                        Ok(float_abi) => base.$key_name = Some(float_abi),
+                        _ => return Some(Err(format!("'{}' is not a valid value for \
+                                                      llvm-floatabi. Use 'soft' or 'hard'.",
+                                                      s))),
+                    }
+                    Some(Ok(()))
+                })).unwrap_or(Ok(()))
+            } );
             ($key_name:ident, RelocModel) => ( {
                 let name = (stringify!($key_name)).replace("_", "-");
                 obj.remove(&name).and_then(|o| o.as_str().and_then(|s| {
@@ -598,6 +610,7 @@ impl Target {
         key!(mcount = "target-mcount");
         key!(llvm_mcount_intrinsic, optional);
         key!(llvm_abiname);
+        key!(llvm_floatabi, FloatAbi)?;
         key!(relax_elf_relocations, bool);
         key!(llvm_args, list);
         key!(use_ctors_section, bool);
@@ -772,6 +785,7 @@ impl ToJson for Target {
         target_option_val!(mcount, "target-mcount");
         target_option_val!(llvm_mcount_intrinsic);
         target_option_val!(llvm_abiname);
+        target_option_val!(llvm_floatabi);
         target_option_val!(relax_elf_relocations);
         target_option_val!(llvm_args);
         target_option_val!(use_ctors_section);

compiler/rustc_target/src/spec/mod.rs

@@ -1085,6 +1085,35 @@ impl ToJson for CodeModel {
     }
 }
 
+/// The float ABI setting to be configured in the LLVM target machine.
+#[derive(Clone, Copy, PartialEq, Hash, Debug)]
+pub enum FloatAbi {
+    Soft,
+    Hard,
+}
+
+impl FromStr for FloatAbi {
+    type Err = ();
+
+    fn from_str(s: &str) -> Result<FloatAbi, ()> {
+        Ok(match s {
+            "soft" => FloatAbi::Soft,
+            "hard" => FloatAbi::Hard,
+            _ => return Err(()),
+        })
+    }
+}
+
+impl ToJson for FloatAbi {
+    fn to_json(&self) -> Json {
+        match *self {
+            FloatAbi::Soft => "soft",
+            FloatAbi::Hard => "hard",
+        }
+        .to_json()
+    }
+}
+
 #[derive(Clone, Copy, PartialEq, Hash, Debug)]
 pub enum TlsModel {
     GeneralDynamic,
@@ -2150,6 +2179,8 @@ pub struct TargetOptions {
     pub env: StaticCow<str>,
     /// ABI name to distinguish multiple ABIs on the same OS and architecture. For instance, `"eabi"`
     /// or `"eabihf"`. Defaults to "".
+    /// This field is *not* forwarded directly to LLVM; its primary purpose is `cfg(target_abi)`.
+    /// However, parts of the backend do check this field for specific values to enable special behavior.
     pub abi: StaticCow<str>,
     /// Vendor name to use for conditional compilation (`target_vendor`). Defaults to "unknown".
     pub vendor: StaticCow<str>,
@@ -2446,8 +2477,17 @@ pub struct TargetOptions {
     pub llvm_mcount_intrinsic: Option<StaticCow<str>>,
 
     /// LLVM ABI name, corresponds to the '-mabi' parameter available in multilib C compilers
+    /// and the `-target-abi` flag in llc. In the LLVM API this is `MCOptions.ABIName`.
     pub llvm_abiname: StaticCow<str>,
 
+    /// Control the float ABI to use, for architectures that support it. The only architecture we
+    /// currently use this for is ARM. Corresponds to the `-float-abi` flag in llc. In the LLVM API
+    /// this is `FloatABIType`. (clang's `-mfloat-abi` is similar but more complicated since it
+    /// can also affect the `soft-float` target feature.)
+    ///
+    /// If not provided, LLVM will infer the float ABI from the target triple (`llvm_target`).
+    pub llvm_floatabi: Option<FloatAbi>,
+
     /// Whether or not RelaxElfRelocation flag will be passed to the linker
     pub relax_elf_relocations: bool,
 
@@ -2719,6 +2759,7 @@ impl Default for TargetOptions {
             mcount: "mcount".into(),
             llvm_mcount_intrinsic: None,
             llvm_abiname: "".into(),
+            llvm_floatabi: None,
             relax_elf_relocations: false,
             llvm_args: cvs![],
             use_ctors_section: false,
@@ -3153,7 +3194,8 @@ impl Target {
             );
         }
 
-        // Check that RISC-V targets always specify which ABI they use.
+        // Check that RISC-V targets always specify which ABI they use,
+        // and that ARM targets specify their float ABI.
         match &*self.arch {
             "riscv32" => {
                 check_matches!(
@@ -3170,6 +3212,9 @@ impl Target {
                     "invalid RISC-V ABI name"
                 );
             }
+            "arm" => {
+                check!(self.llvm_floatabi.is_some(), "ARM targets must specify their float ABI",)
+            }
             _ => {}
         }
 

compiler/rustc_target/src/spec/targets/arm_linux_androideabi.rs

@@ -1,4 +1,4 @@
-use crate::spec::{SanitizerSet, Target, TargetOptions, base};
+use crate::spec::{FloatAbi, SanitizerSet, Target, TargetOptions, base};
 
 pub(crate) fn target() -> Target {
     Target {
@@ -14,6 +14,7 @@ pub(crate) fn target() -> Target {
         arch: "arm".into(),
         options: TargetOptions {
             abi: "eabi".into(),
+            llvm_floatabi: Some(FloatAbi::Soft),
             // https://developer.android.com/ndk/guides/abis.html#armeabi
             features: "+strict-align,+v5te".into(),
             supported_sanitizers: SanitizerSet::ADDRESS,

compiler/rustc_target/src/spec/targets/arm_unknown_linux_gnueabi.rs

@@ -1,4 +1,4 @@
-use crate::spec::{Target, TargetOptions, base};
+use crate::spec::{FloatAbi, Target, TargetOptions, base};
 
 pub(crate) fn target() -> Target {
     Target {
@@ -14,6 +14,7 @@ pub(crate) fn target() -> Target {
         arch: "arm".into(),
         options: TargetOptions {
             abi: "eabi".into(),
+            llvm_floatabi: Some(FloatAbi::Soft),
             features: "+strict-align,+v6".into(),
             max_atomic_width: Some(64),
             mcount: "\u{1}__gnu_mcount_nc".into(),

compiler/rustc_target/src/spec/targets/arm_unknown_linux_gnueabihf.rs

@@ -1,4 +1,4 @@
-use crate::spec::{Target, TargetOptions, base};
+use crate::spec::{FloatAbi, Target, TargetOptions, base};
 
 pub(crate) fn target() -> Target {
     Target {
@@ -14,6 +14,7 @@ pub(crate) fn target() -> Target {
         arch: "arm".into(),
         options: TargetOptions {
             abi: "eabihf".into(),
+            llvm_floatabi: Some(FloatAbi::Hard),
             features: "+strict-align,+v6,+vfp2,-d32".into(),
             max_atomic_width: Some(64),
             mcount: "\u{1}__gnu_mcount_nc".into(),

compiler/rustc_target/src/spec/targets/arm_unknown_linux_musleabi.rs

@@ -1,11 +1,8 @@
-use crate::spec::{Target, TargetOptions, base};
+use crate::spec::{FloatAbi, Target, TargetOptions, base};
 
 pub(crate) fn target() -> Target {
     Target {
-        // It's important we use "gnueabi" and not "musleabi" here. LLVM uses it
-        // to determine the calling convention and float ABI, and it doesn't
-        // support the "musleabi" value.
-        llvm_target: "arm-unknown-linux-gnueabi".into(),
+        llvm_target: "arm-unknown-linux-musleabi".into(),
         metadata: crate::spec::TargetMetadata {
             description: Some("Armv6 Linux with musl 1.2.3".into()),
             tier: Some(2),
@@ -17,6 +14,7 @@ pub(crate) fn target() -> Target {
         arch: "arm".into(),
         options: TargetOptions {
             abi: "eabi".into(),
+            llvm_floatabi: Some(FloatAbi::Soft),
             // Most of these settings are copied from the arm_unknown_linux_gnueabi
             // target.
             features: "+strict-align,+v6".into(),

compiler/rustc_target/src/spec/targets/arm_unknown_linux_musleabihf.rs

@@ -1,11 +1,8 @@
-use crate::spec::{Target, TargetOptions, base};
+use crate::spec::{FloatAbi, Target, TargetOptions, base};
 
 pub(crate) fn target() -> Target {
     Target {
-        // It's important we use "gnueabihf" and not "musleabihf" here. LLVM
-        // uses it to determine the calling convention and float ABI, and it
-        // doesn't support the "musleabihf" value.
-        llvm_target: "arm-unknown-linux-gnueabihf".into(),
+        llvm_target: "arm-unknown-linux-musleabihf".into(),
         metadata: crate::spec::TargetMetadata {
             description: Some("Armv6 Linux with musl 1.2.3, hardfloat".into()),
             tier: Some(2),
@@ -17,6 +14,7 @@ pub(crate) fn target() -> Target {
         arch: "arm".into(),
         options: TargetOptions {
             abi: "eabihf".into(),
+            llvm_floatabi: Some(FloatAbi::Hard),
             // Most of these settings are copied from the arm_unknown_linux_gnueabihf
             // target.
             features: "+strict-align,+v6,+vfp2,-d32".into(),