Rollup merge of #134932 - RalfJung:arm-float-abi, r=workingjubilee

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 https://github.com/rust-lang/rust/pull/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...

3 files changed, 26 insertions, 9 deletions

diff --git a/compiler/rustc_codegen_llvm/src/back/owned_target_machine.rs b/compiler/rustc_codegen_llvm/src/back/owned_target_machine.rs
index 44c30d22a9e..4cbd49aa44d 100644
--- a/compiler/rustc_codegen_llvm/src/back/owned_target_machine.rs
+++ b/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,
diff --git a/compiler/rustc_codegen_llvm/src/back/write.rs b/compiler/rustc_codegen_llvm/src/back/write.rs
index ae5e818d86f..806f810627d 100644
--- a/compiler/rustc_codegen_llvm/src/back/write.rs
+++ b/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,
diff --git a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
index 9a2bfd95562..128a147963b 100644
--- a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
+++ b/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,