Support homogeneous aggregates for hard-float ARM

Hard-float ARM targets use the AACPS-VFP ABI, which passes and returns
homogeneous float/vector aggregates in the VFP registers.

Fixes rust-lang#43329.

src/librustc_trans/cabi_arm.rs

@@ -8,14 +8,50 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use abi::{FnType, ArgType, LayoutExt, Reg, Uniform};
+use abi::{FnType, ArgType, LayoutExt, Reg, RegKind, Uniform};
 use context::CrateContext;
+use llvm::CallConv;
 
-fn classify_ret_ty<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>, ret: &mut ArgType<'tcx>) {
+fn is_homogeneous_aggregate<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>, arg: &mut ArgType<'tcx>)
+                                     -> Option<Uniform> {
+    arg.layout.homogeneous_aggregate(ccx).and_then(|unit| {
+        let size = arg.layout.size(ccx);
+
+        // Ensure we have at most four uniquely addressable members.
+        if size > unit.size.checked_mul(4, ccx).unwrap() {
+            return None;
+        }
+
+        let valid_unit = match unit.kind {
+            RegKind::Integer => false,
+            RegKind::Float => true,
+            RegKind::Vector => size.bits() == 64 || size.bits() == 128
+        };
+
+        if valid_unit {
+            Some(Uniform {
+                unit,
+                total: size
+            })
+        } else {
+            None
+        }
+    })
+}
+
+fn classify_ret_ty<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>, ret: &mut ArgType<'tcx>, vfp: bool) {
     if !ret.layout.is_aggregate() {
         ret.extend_integer_width_to(32);
         return;
     }
+
+    if vfp {
+        if let Some(uniform) = is_homogeneous_aggregate(ccx, ret) {
+            ret.cast_to(ccx, uniform);
+            return;
+        }
+    }
+
     let size = ret.layout.size(ccx);
     let bits = size.bits();
     if bits <= 32 {
@@ -35,11 +71,19 @@ fn classify_ret_ty<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>, ret: &mut ArgType<'tc
     ret.make_indirect(ccx);
 }
 
-fn classify_arg_ty<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>, arg: &mut ArgType<'tcx>) {
+fn classify_arg_ty<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>, arg: &mut ArgType<'tcx>, vfp: bool) {
     if !arg.layout.is_aggregate() {
         arg.extend_integer_width_to(32);
         return;
     }
+
+    if vfp {
+        if let Some(uniform) = is_homogeneous_aggregate(ccx, arg) {
+            arg.cast_to(ccx, uniform);
+            return;
+        }
+    }
+
     let align = arg.layout.align(ccx).abi();
     let total = arg.layout.size(ccx);
     arg.cast_to(ccx, Uniform {
@@ -49,12 +93,18 @@ fn classify_arg_ty<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>, arg: &mut ArgType<'tc
 }
 
 pub fn compute_abi_info<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>, fty: &mut FnType<'tcx>) {
+    // If this is a target with a hard-float ABI, and the function is not explicitly
+    // `extern "aapcs"`, then we must use the VFP registers for homogeneous aggregates.
+    let vfp = ccx.sess().target.target.llvm_target.ends_with("hf")
+        && fty.cconv != CallConv::ArmAapcsCallConv
+        && !fty.variadic;
+
     if !fty.ret.is_ignore() {
-        classify_ret_ty(ccx, &mut fty.ret);
+        classify_ret_ty(ccx, &mut fty.ret, vfp);
     }
 
     for arg in &mut fty.args {
         if arg.is_ignore() { continue; }
-        classify_arg_ty(ccx, arg);
+        classify_arg_ty(ccx, arg, vfp);
     }
 }