Implement passing arguments by ref for win64 ABI

Author: teapotd

cranelift/codegen/src/abi.rs

@@ -54,6 +54,9 @@ pub enum ValueConversion {
 
     /// Unsigned zero-extend value to the required type.
     Uext(Type),
+
+    /// Pass value by pointer of given integer type.
+    Pointer(Type),
 }
 
 impl ValueConversion {
@@ -63,7 +66,7 @@ impl ValueConversion {
             Self::IntSplit => ty.half_width().expect("Integer type too small to split"),
             Self::VectorSplit => ty.half_vector().expect("Not a vector"),
             Self::IntBits => Type::int(ty.bits()).expect("Bad integer size"),
-            Self::Sext(nty) | Self::Uext(nty) => nty,
+            Self::Sext(nty) | Self::Uext(nty) | Self::Pointer(nty) => nty,
         }
     }
 
@@ -74,6 +77,11 @@ impl ValueConversion {
             _ => false,
         }
     }
+
+    /// Is this a conversion to pointer?
+    pub fn is_pointer(self) -> bool {
+        matches!(self, Self::Pointer(_))
+    }
 }
 
 /// Common trait for assigning arguments to registers or stack locations.
@@ -110,10 +118,16 @@ pub fn legalize_args<AA: ArgAssigner>(args: &[AbiParam], aa: &mut AA) -> Option<
             }
             // Split this argument into two smaller ones. Then revisit both.
             ArgAction::Convert(conv) => {
+                debug_assert!(
+                    !arg.legalized_to_pointer,
+                    "No more conversions allowed after conversion to pointer"
+                );
                 let value_type = conv.apply(arg.value_type);
-                let new_arg = AbiParam { value_type, ..arg };
                 args.to_mut()[argno].value_type = value_type;
-                if conv.is_split() {
+                if conv.is_pointer() {
+                    args.to_mut()[argno].legalized_to_pointer = true;
+                } else if conv.is_split() {
+                    let new_arg = AbiParam { value_type, ..arg };
                     args.to_mut().insert(argno + 1, new_arg);
                 }
             }
@@ -152,6 +166,10 @@ pub fn legalize_abi_value(have: Type, arg: &AbiParam) -> ValueConversion {
     let have_bits = have.bits();
     let arg_bits = arg.value_type.bits();
 
+    if arg.legalized_to_pointer {
+        return ValueConversion::Pointer(arg.value_type);
+    }
+
     match have_bits.cmp(&arg_bits) {
         // We have fewer bits than the ABI argument.
         Ordering::Less => {
@@ -226,5 +244,12 @@ mod tests {
             legalize_abi_value(types::F64, &arg),
             ValueConversion::IntBits
         );
+
+        // Value is passed by reference
+        arg.legalized_to_pointer = true;
+        assert_eq!(
+            legalize_abi_value(types::F64, &arg),
+            ValueConversion::Pointer(types::I32)
+        );
     }
 }

cranelift/codegen/src/ir/extfunc.rs

@@ -156,6 +156,8 @@ pub struct AbiParam {
     /// ABI-specific location of this argument, or `Unassigned` for arguments that have not yet
     /// been legalized.
     pub location: ArgumentLoc,
+    /// Was the argument converted to pointer during legalization?
+    pub legalized_to_pointer: bool,
 }
 
 impl AbiParam {
@@ -166,6 +168,7 @@ impl AbiParam {
             extension: ArgumentExtension::None,
             purpose: ArgumentPurpose::Normal,
             location: Default::default(),
+            legalized_to_pointer: false,
         }
     }
 
@@ -176,6 +179,7 @@ impl AbiParam {
             extension: ArgumentExtension::None,
             purpose,
             location: Default::default(),
+            legalized_to_pointer: false,
         }
     }
 
@@ -186,6 +190,7 @@ impl AbiParam {
             extension: ArgumentExtension::None,
             purpose,
             location: ArgumentLoc::Reg(regunit),
+            legalized_to_pointer: false,
         }
     }
 
@@ -219,6 +224,9 @@ pub struct DisplayAbiParam<'a>(&'a AbiParam, Option<&'a RegInfo>);
 impl<'a> fmt::Display for DisplayAbiParam<'a> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         write!(f, "{}", self.0.value_type)?;
+        if self.0.legalized_to_pointer {
+            write!(f, " ptr")?;
+        }
         match self.0.extension {
             ArgumentExtension::None => {}
             ArgumentExtension::Uext => write!(f, " uext")?,
@@ -415,6 +423,8 @@ mod tests {
         assert_eq!(t.sext().to_string(), "i32 sext");
         t.purpose = ArgumentPurpose::StructReturn;
         assert_eq!(t.to_string(), "i32 uext sret");
+        t.legalized_to_pointer = true;
+        assert_eq!(t.to_string(), "i32 ptr uext sret");
     }
 
     #[test]

cranelift/codegen/src/isa/x86/abi.rs

@@ -70,6 +70,7 @@ struct Args {
     shared_flags: shared_settings::Flags,
     #[allow(dead_code)]
     isa_flags: isa_settings::Flags,
+    is_rets: bool,
 }
 
 impl Args {
@@ -80,6 +81,7 @@ impl Args {
         call_conv: CallConv,
         shared_flags: &shared_settings::Flags,
         isa_flags: &isa_settings::Flags,
+        is_rets: bool,
     ) -> Self {
         let offset = if call_conv.extends_windows_fastcall() {
             WIN_SHADOW_STACK_SPACE
@@ -99,6 +101,7 @@ impl Args {
             call_conv,
             shared_flags: shared_flags.clone(),
             isa_flags: isa_flags.clone(),
+            is_rets,
         }
     }
 }
@@ -107,6 +110,17 @@ impl ArgAssigner for Args {
     fn assign(&mut self, arg: &AbiParam) -> ArgAction {
         let ty = arg.value_type;
 
+        if ty.bits() > u16::from(self.pointer_bits) {
+            if !self.is_rets && self.call_conv.extends_windows_fastcall() {
+                // "Any argument that doesn't fit in 8 bytes, or isn't
+                // 1, 2, 4, or 8 bytes, must be passed by reference"
+                return ValueConversion::Pointer(self.pointer_type).into();
+            } else if !ty.is_vector() && !ty.is_float() {
+                // On SystemV large integers and booleans are broken down to fit in a register.
+                return ValueConversion::IntSplit.into();
+            }
+        }
+
         // Vectors should stay in vector registers unless SIMD is not enabled--then they are split
         if ty.is_vector() {
             if self.shared_flags.enable_simd() {
@@ -117,11 +131,6 @@ impl ArgAssigner for Args {
             return ValueConversion::VectorSplit.into();
         }
 
-        // Large integers and booleans are broken down to fit in a register.
-        if !ty.is_float() && ty.bits() > u16::from(self.pointer_bits) {
-            return ValueConversion::IntSplit.into();
-        }
-
         // Small integers are extended to the size of a pointer register.
         if ty.is_int() && ty.bits() < u16::from(self.pointer_bits) {
             match arg.extension {
@@ -203,7 +212,7 @@ pub fn legalize_signature(
         PointerWidth::U16 => panic!(),
         PointerWidth::U32 => {
             bits = 32;
-            args = Args::new(bits, &[], 0, sig.call_conv, shared_flags, isa_flags);
+            args = Args::new(bits, &[], 0, sig.call_conv, shared_flags, isa_flags, false);
         }
         PointerWidth::U64 => {
             bits = 64;
@@ -215,6 +224,7 @@ pub fn legalize_signature(
                     sig.call_conv,
                     shared_flags,
                     isa_flags,
+                    false,
                 )
             } else {
                 Args::new(
@@ -224,6 +234,7 @@ pub fn legalize_signature(
                     sig.call_conv,
                     shared_flags,
                     isa_flags,
+                    false,
                 )
             };
         }
@@ -243,6 +254,7 @@ pub fn legalize_signature(
         sig.call_conv,
         shared_flags,
         isa_flags,
+        true,
     );
 
     // If we don't have enough available return registers
@@ -267,6 +279,7 @@ pub fn legalize_signature(
                 purpose: ArgumentPurpose::StructReturn,
                 extension: ArgumentExtension::None,
                 location: ArgumentLoc::Unassigned,
+                legalized_to_pointer: false,
             };
             match args.assign(&ret_ptr_param) {
                 ArgAction::Assign(ArgumentLoc::Reg(reg)) => {
@@ -283,6 +296,7 @@ pub fn legalize_signature(
                 purpose: ArgumentPurpose::StructReturn,
                 extension: ArgumentExtension::None,
                 location: ArgumentLoc::Unassigned,
+                legalized_to_pointer: false,
             };
             match backup_rets.assign(&ret_ptr_return) {
                 ArgAction::Assign(ArgumentLoc::Reg(reg)) => {

cranelift/codegen/src/legalizer/boundary.rs

@@ -504,6 +504,13 @@ where
             // this value.
             pos.ins().with_results([into_result]).ireduce(ty, arg)
         }
+        // ABI argument is a pointer to the value we want.
+        ValueConversion::Pointer(abi_ty) => {
+            let arg = convert_from_abi(pos, abi_ty, None, get_arg);
+            pos.ins()
+                .with_results([into_result])
+                .load(ty, MemFlags::new(), arg, 0)
+        }
     }
 }
 
@@ -563,6 +570,18 @@ fn convert_to_abi<PutArg>(
             let arg = pos.ins().uextend(abi_ty, value);
             convert_to_abi(pos, cfg, arg, put_arg);
         }
+        ValueConversion::Pointer(abi_ty) => {
+            // Note: This conversion can only happen for call arguments,
+            // so we can allocate the value on stack safely.
+            let stack_slot = pos.func.create_stack_slot(StackSlotData {
+                kind: StackSlotKind::ExplicitSlot,
+                size: ty.bytes(),
+                offset: None,
+            });
+            let arg = pos.ins().stack_addr(abi_ty, stack_slot, 0);
+            pos.ins().store(MemFlags::new(), value, arg, 0);
+            convert_to_abi(pos, cfg, arg, put_arg);
+        }
     }
 }
 
@@ -815,7 +834,12 @@ pub fn handle_return_abi(inst: Inst, func: &mut Function, cfg: &ControlFlowGraph
     pos.use_srcloc(inst);
 
     legalize_inst_arguments(pos, cfg, abi_args, |func, abi_arg| {
-        func.signature.returns[abi_arg]
+        let arg = func.signature.returns[abi_arg];
+        debug_assert!(
+            !arg.legalized_to_pointer,
+            "Return value cannot be legalized to pointer"
+        );
+        arg
     });
     // Append special return arguments for any `sret`, `link`, and `vmctx` return values added to
     // the legalized signature. These values should simply be propagated from the entry block

cranelift/filetests/filetests/isa/x86/windows_fastcall_x64.clif

@@ -117,6 +117,20 @@ block0(v0: i64, v1: i64):
 }
 ; check: function %ret_val_i128(i64 [%rdx], i64 [%r8], i64 sret [%rcx], i64 fp [%rbp]) -> i64 sret [%rax], i64 fp [%rbp] windows_fastcall {
 
+; check if i128 is passed by reference
+function %i128_arg(i128) windows_fastcall {
+block0(v0: i128):
+    return
+}
+; check: function %i128_arg(i64 ptr [%rcx], i64 fp [%rbp]) -> i64 fp [%rbp] windows_fastcall {
+
+; check if vector types are passed by reference
+function %i32x4_arg(i32x4) windows_fastcall {
+block0(v0: i32x4):
+    return
+}
+; check: function %i32x4_arg(i64 ptr [%rcx], i64 fp [%rbp]) -> i64 fp [%rbp] windows_fastcall {
+
 function %internal_stack_arg_function_call(i64) -> i64 windows_fastcall {
   fn0 = %foo(i64, i64, i64, i64) -> i64 windows_fastcall
   fn1 = %foo2(i64, i64, i64, i64) -> i64 windows_fastcall

cranelift/filetests/filetests/legalizer/pass_by_ref.clif

@@ -0,0 +1,35 @@
+test compile
+set opt_level=speed_and_size
+set is_pic
+target x86_64 haswell
+
+function %legalize_entry(i128) -> i64 windows_fastcall {
+block0(v0: i128):
+    v1, v2 = isplit v0
+    return v2
+}
+; check:  function %legalize_entry(i64 ptr [%rcx], i64 fp [%rbp]) -> i64 [%rax], i64 fp [%rbp] windows_fastcall {
+; check:  block0(v3: i64 [%rcx], v6: i64 [%rbp]):
+; nextln:     x86_push v6
+; nextln:     copy_special %rsp -> %rbp
+; nextln:     v4 = load.i64 v3
+; nextln:     v1 -> v4
+; nextln:     v5 = load.i64 v3+8
+; nextln:     v2 -> v5
+; nextln:     v7 = x86_pop.i64
+; nextln:     return v5, v7
+
+function %legalize_call() {
+    fn0 = %foo(i32x4) windows_fastcall
+block0:
+    v0 = vconst.i32x4 [1 2 3 4]
+    call fn0(v0)
+    return
+}
+; check:  ss0 = explicit_slot 16, offset -32
+; check:  sig0 = (i64 ptr [%rcx]) windows_fastcall
+; check:  v0 = vconst.i32x4 const0
+; nextln: v1 = stack_addr.i64 ss0
+; nextln: store v0, v1
+; nextln: regmove v1, %rax -> %rcx
+; nextln: call fn0(v1)