Rollup merge of #47964 - jcowgill:mips64-abi, r=eddyb

rustc_trans: rewrite mips64 ABI code

This PR rewrites the ABI handling code for 64-bit MIPS and should fix various FFI issues including #47290.

To accomodate the 64-bit ABI I have had to add a new `CastTarget` variant which I've called `Chunked` (though maybe this isn't the best name). This allows an ABI to cast to some arbitrary structure of `Reg` types. This is required on MIPS which might need to cast to a structure containing a mixture of `i64` and `f64` types.

3 files changed, 188 insertions, 76 deletions

diff --git a/src/librustc_trans/abi.rs b/src/librustc_trans/abi.rs
index 12698964d2e..ee0f2415bd8 100644
--- a/src/librustc_trans/abi.rs
+++ b/src/librustc_trans/abi.rs
@@ -40,7 +40,7 @@ use rustc::ty::layout::{self, Align, Size, TyLayout};
 use rustc::ty::layout::{HasDataLayout, LayoutOf};
 
 use libc::c_uint;
-use std::{cmp, iter};
+use std::cmp;
 
 pub use syntax::abi::Abi;
 pub use rustc::ty::layout::{FAT_PTR_ADDR, FAT_PTR_EXTRA};
@@ -279,30 +279,6 @@ impl Uniform {
     pub fn align(&self, cx: &CodegenCx) -> Align {
         self.unit.align(cx)
     }
-
-    pub fn llvm_type(&self, cx: &CodegenCx) -> Type {
-        let llunit = self.unit.llvm_type(cx);
-
-        if self.total <= self.unit.size {
-            return llunit;
-        }
-
-        let count = self.total.bytes() / self.unit.size.bytes();
-        let rem_bytes = self.total.bytes() % self.unit.size.bytes();
-
-        if rem_bytes == 0 {
-            return Type::array(&llunit, count);
-        }
-
-        // Only integers can be really split further.
-        assert_eq!(self.unit.kind, RegKind::Integer);
-
-        let args: Vec<_> = (0..count).map(|_| llunit)
-            .chain(iter::once(Type::ix(cx, rem_bytes * 8)))
-            .collect();
-
-        Type::struct_(cx, &args, false)
-    }
 }
 
 pub trait LayoutExt<'tcx> {
@@ -405,55 +381,81 @@ impl<'tcx> LayoutExt<'tcx> for TyLayout<'tcx> {
 }
 
 #[derive(Clone, Copy, PartialEq, Eq, Debug)]
-pub enum CastTarget {
-    Uniform(Uniform),
-    Pair(Reg, Reg)
+pub struct CastTarget {
+    pub prefix: [Option<RegKind>; 8],
+    pub prefix_chunk: Size,
+    pub rest: Uniform,
 }
 
 impl From<Reg> for CastTarget {
     fn from(unit: Reg) -> CastTarget {
-        CastTarget::Uniform(Uniform::from(unit))
+        CastTarget::from(Uniform::from(unit))
     }
 }
 
 impl From<Uniform> for CastTarget {
     fn from(uniform: Uniform) -> CastTarget {
-        CastTarget::Uniform(uniform)
+        CastTarget {
+            prefix: [None; 8],
+            prefix_chunk: Size::from_bytes(0),
+            rest: uniform
+        }
     }
 }
 
 impl CastTarget {
-    pub fn size(&self, cx: &CodegenCx) -> Size {
-        match *self {
-            CastTarget::Uniform(u) => u.total,
-            CastTarget::Pair(a, b) => {
-                (a.size.abi_align(a.align(cx)) + b.size)
-                    .abi_align(self.align(cx))
-            }
+    pub fn pair(a: Reg, b: Reg) -> CastTarget {
+        CastTarget {
+            prefix: [Some(a.kind), None, None, None, None, None, None, None],
+            prefix_chunk: a.size,
+            rest: Uniform::from(b)
         }
     }
 
+    pub fn size(&self, cx: &CodegenCx) -> Size {
+        (self.prefix_chunk * self.prefix.iter().filter(|x| x.is_some()).count() as u64)
+            .abi_align(self.rest.align(cx)) + self.rest.total
+    }
+
     pub fn align(&self, cx: &CodegenCx) -> Align {
-        match *self {
-            CastTarget::Uniform(u) => u.align(cx),
-            CastTarget::Pair(a, b) => {
-                cx.data_layout().aggregate_align
-                    .max(a.align(cx))
-                    .max(b.align(cx))
-            }
-        }
+        self.prefix.iter()
+            .filter_map(|x| x.map(|kind| Reg { kind: kind, size: self.prefix_chunk }.align(cx)))
+            .fold(cx.data_layout().aggregate_align.max(self.rest.align(cx)),
+                |acc, align| acc.max(align))
     }
 
     pub fn llvm_type(&self, cx: &CodegenCx) -> Type {
-        match *self {
-            CastTarget::Uniform(u) => u.llvm_type(cx),
-            CastTarget::Pair(a, b) => {
-                Type::struct_(cx, &[
-                    a.llvm_type(cx),
-                    b.llvm_type(cx)
-                ], false)
+        let rest_ll_unit = self.rest.unit.llvm_type(cx);
+        let rest_count = self.rest.total.bytes() / self.rest.unit.size.bytes();
+        let rem_bytes = self.rest.total.bytes() % self.rest.unit.size.bytes();
+
+        if self.prefix.iter().all(|x| x.is_none()) {
+            // Simplify to a single unit when there is no prefix and size <= unit size
+            if self.rest.total <= self.rest.unit.size {
+                return rest_ll_unit;
+            }
+
+            // Simplify to array when all chunks are the same size and type
+            if rem_bytes == 0 {
+                return Type::array(&rest_ll_unit, rest_count);
             }
         }
+
+        // Create list of fields in the main structure
+        let mut args: Vec<_> =
+            self.prefix.iter().flat_map(|option_kind| option_kind.map(
+                    |kind| Reg { kind: kind, size: self.prefix_chunk }.llvm_type(cx)))
+            .chain((0..rest_count).map(|_| rest_ll_unit))
+            .collect();
+
+        // Append final integer
+        if rem_bytes != 0 {
+            // Only integers can be really split further.
+            assert_eq!(self.rest.unit.kind, RegKind::Integer);
+            args.push(Type::ix(cx, rem_bytes * 8));
+        }
+
+        Type::struct_(cx, &args, false)
     }
 }
 
diff --git a/src/librustc_trans/cabi_mips64.rs b/src/librustc_trans/cabi_mips64.rs
index e44063faab8..94bf53cee1e 100644
--- a/src/librustc_trans/cabi_mips64.rs
+++ b/src/librustc_trans/cabi_mips64.rs
@@ -8,50 +8,160 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use abi::{ArgType, FnType, LayoutExt, Reg, Uniform};
+use abi::{ArgAttribute, ArgType, CastTarget, FnType, LayoutExt, PassMode, Reg, RegKind, Uniform};
 use context::CodegenCx;
+use rustc::ty::layout::{self, Size};
 
-use rustc::ty::layout::Size;
+fn extend_integer_width_mips(arg: &mut ArgType, bits: u64) {
+    // Always sign extend u32 values on 64-bit mips
+    if let layout::Abi::Scalar(ref scalar) = arg.layout.abi {
+        if let layout::Int(i, signed) = scalar.value {
+            if !signed && i.size().bits() == 32 {
+                if let PassMode::Direct(ref mut attrs) = arg.mode {
+                    attrs.set(ArgAttribute::SExt);
+                    return;
+                }
+            }
+        }
+    }
+
+    arg.extend_integer_width_to(bits);
+}
+
+fn bits_to_int_reg(bits: u64) -> Reg {
+    if bits <= 8 {
+        Reg::i8()
+    } else if bits <= 16 {
+        Reg::i16()
+    } else if bits <= 32 {
+        Reg::i32()
+    } else {
+        Reg::i64()
+    }
+}
 
-fn classify_ret_ty<'a, 'tcx>(cx: &CodegenCx<'a, 'tcx>,
-                             ret: &mut ArgType<'tcx>,
-                             offset: &mut Size) {
+fn float_reg<'a, 'tcx>(cx: &CodegenCx<'a, 'tcx>, ret: &ArgType<'tcx>, i: usize) -> Option<Reg> {
+    match ret.layout.field(cx, i).abi {
+        layout::Abi::Scalar(ref scalar) => match scalar.value {
+            layout::F32 => Some(Reg::f32()),
+            layout::F64 => Some(Reg::f64()),
+            _ => None
+        },
+        _ => None
+    }
+}
+
+fn classify_ret_ty<'a, 'tcx>(cx: &CodegenCx<'a, 'tcx>, ret: &mut ArgType<'tcx>) {
     if !ret.layout.is_aggregate() {
-        ret.extend_integer_width_to(64);
+        extend_integer_width_mips(ret, 64);
+        return;
+    }
+
+    let size = ret.layout.size;
+    let bits = size.bits();
+    if bits <= 128 {
+        // Unlike other architectures which return aggregates in registers, MIPS n64 limits the
+        // use of float registers to structures (not unions) containing exactly one or two
+        // float fields.
+
+        if let layout::FieldPlacement::Arbitrary { .. } = ret.layout.fields {
+            if ret.layout.fields.count() == 1 {
+                if let Some(reg) = float_reg(cx, ret, 0) {
+                    ret.cast_to(reg);
+                    return;
+                }
+            } else if ret.layout.fields.count() == 2 {
+                if let Some(reg0) = float_reg(cx, ret, 0) {
+                    if let Some(reg1) = float_reg(cx, ret, 1) {
+                        ret.cast_to(CastTarget::pair(reg0, reg1));
+                        return;
+                    }
+                }
+            }
+        }
+
+        // Cast to a uniform int structure
+        ret.cast_to(Uniform {
+            unit: bits_to_int_reg(bits),
+            total: size
+        });
     } else {
         ret.make_indirect();
-        *offset += cx.tcx.data_layout.pointer_size;
     }
 }
 
-fn classify_arg_ty(cx: &CodegenCx, arg: &mut ArgType, offset: &mut Size) {
+fn classify_arg_ty<'a, 'tcx>(cx: &CodegenCx<'a, 'tcx>, arg: &mut ArgType<'tcx>) {
+    if !arg.layout.is_aggregate() {
+        extend_integer_width_mips(arg, 64);
+        return;
+    }
+
     let dl = &cx.tcx.data_layout;
     let size = arg.layout.size;
-    let align = arg.layout.align.max(dl.i32_align).min(dl.i64_align);
+    let mut prefix = [None; 8];
+    let mut prefix_index = 0;
 
-    if arg.layout.is_aggregate() {
-        arg.cast_to(Uniform {
-            unit: Reg::i64(),
-            total: size
-        });
-        if !offset.is_abi_aligned(align) {
-            arg.pad_with(Reg::i64());
+    match arg.layout.fields {
+        layout::FieldPlacement::Array { .. } => {
+            // Arrays are passed indirectly
+            arg.make_indirect();
+            return;
         }
-    } else {
-        arg.extend_integer_width_to(64);
-    }
+        layout::FieldPlacement::Union(_) => {
+            // Unions and are always treated as a series of 64-bit integer chunks
+        },
+        layout::FieldPlacement::Arbitrary { .. } => {
+            // Structures are split up into a series of 64-bit integer chunks, but any aligned
+            // doubles not part of another aggregate are passed as floats.
+            let mut last_offset = Size::from_bytes(0);
+
+            for i in 0..arg.layout.fields.count() {
+                let field = arg.layout.field(cx, i);
+                let offset = arg.layout.fields.offset(i);
+
+                // We only care about aligned doubles
+                if let layout::Abi::Scalar(ref scalar) = field.abi {
+                    if let layout::F64 = scalar.value {
+                        if offset.is_abi_aligned(dl.f64_align) {
+                            // Insert enough integers to cover [last_offset, offset)
+                            assert!(last_offset.is_abi_aligned(dl.f64_align));
+                            for _ in 0..((offset - last_offset).bits() / 64)
+                                .min((prefix.len() - prefix_index) as u64) {
+
+                                prefix[prefix_index] = Some(RegKind::Integer);
+                                prefix_index += 1;
+                            }
+
+                            if prefix_index == prefix.len() {
+                                break;
+                            }
+
+                            prefix[prefix_index] = Some(RegKind::Float);
+                            prefix_index += 1;
+                            last_offset = offset + Reg::f64().size;
+                        }
+                    }
+                }
+            }
+        }
+    };
 
-    *offset = offset.abi_align(align) + size.abi_align(align);
+    // Extract first 8 chunks as the prefix
+    let rest_size = size - Size::from_bytes(8) * prefix_index as u64;
+    arg.cast_to(CastTarget {
+        prefix: prefix,
+        prefix_chunk: Size::from_bytes(8),
+        rest: Uniform { unit: Reg::i64(), total: rest_size }
+    });
 }
 
 pub fn compute_abi_info<'a, 'tcx>(cx: &CodegenCx<'a, 'tcx>, fty: &mut FnType<'tcx>) {
-    let mut offset = Size::from_bytes(0);
     if !fty.ret.is_ignore() {
-        classify_ret_ty(cx, &mut fty.ret, &mut offset);
+        classify_ret_ty(cx, &mut fty.ret);
     }
 
     for arg in &mut fty.args {
         if arg.is_ignore() { continue; }
-        classify_arg_ty(cx, arg, &mut offset);
+        classify_arg_ty(cx, arg);
     }
 }
diff --git a/src/librustc_trans/cabi_x86_64.rs b/src/librustc_trans/cabi_x86_64.rs
index b8144a3ca7a..7eadaa7f493 100644
--- a/src/librustc_trans/cabi_x86_64.rs
+++ b/src/librustc_trans/cabi_x86_64.rs
@@ -171,7 +171,7 @@ fn cast_target(cls: &[Option<Class>], size: Size) -> CastTarget {
     let mut target = CastTarget::from(lo);
     if size > offset {
         if let Some(hi) = reg_component(cls, &mut i, size - offset) {
-            target = CastTarget::Pair(lo, hi);
+            target = CastTarget::pair(lo, hi);
         }
     }
     assert_eq!(reg_component(cls, &mut i, Size::from_bytes(0)), None);