Transmute intrinsics (#6692)

## Description

This PR implements the `__transmute` intrinsic. As Rust this intrinsic
should be a no-op semantically equal to a pointer cast. Although this PR
does not aim that it is 100% no-op yet.

At the moment some trade-offs were taken:

1 - References, pointers etc... are not allowed at the moment;
2 - `u16` and `u32` actually occupy 64bits. To allow transmute to work
in complex aggregates, this PR is accepting them as `u64`. Doing
otherwise would forbid `__transmute` to be no-op. Specially in complex
aggregates;

## Checklist

- [ ] I have linked to any relevant issues.
- [x] I have commented my code, particularly in hard-to-understand
areas.
- [ ] I have updated the documentation where relevant (API docs, the
reference, and the Sway book).
- [ ] If my change requires substantial documentation changes, I have
[requested support from the DevRel
team](https://github.com/FuelLabs/devrel-requests/issues/new/choose)
- [x] I have added tests that prove my fix is effective or that my
feature works.
- [ ] I have added (or requested a maintainer to add) the necessary
`Breaking*` or `New Feature` labels where relevant.
- [x] I have done my best to ensure that my PR adheres to [the Fuel Labs
Code Review
Standards](https://github.com/FuelLabs/rfcs/blob/master/text/code-standards/external-contributors.md).
- [ ] I have requested a review from the relevant team or maintainers.

---------

Co-authored-by: João Matos <[email protected]>

sway-ast/src/intrinsics.rs

@@ -43,6 +43,7 @@ pub enum Intrinsic {
     EncodeBufferAsRawSlice, // let slice: raw_slice = __encode_buffer_as_raw_slice(buffer)
     Slice, // let ref_to_slice = __slice::<T: array or ref_to_slice>(item: T, inclusive_start_index, exclusive_end_index)
     ElemAt, // let elem: &T = __elem_at::<T: array or ref_to_slice>(item: T, index)
+    Transmute, // let dst: B = __transmute::<A, B>(src)
 }
 
 impl fmt::Display for Intrinsic {
@@ -89,6 +90,7 @@ impl fmt::Display for Intrinsic {
             Intrinsic::EncodeBufferAsRawSlice => "encode_buffer_as_raw_slice",
             Intrinsic::Slice => "slice",
             Intrinsic::ElemAt => "elem_at",
+            Intrinsic::Transmute => "transmute",
         };
         write!(f, "{s}")
     }
@@ -139,6 +141,7 @@ impl Intrinsic {
             "__encode_buffer_as_raw_slice" => EncodeBufferAsRawSlice,
             "__slice" => Slice,
             "__elem_at" => ElemAt,
+            "__transmute" => Transmute,
             _ => return None,
         })
     }

sway-core/src/ir_generation/const_eval.rs

@@ -1,4 +1,7 @@
-use std::ops::{BitAnd, BitOr, BitXor, Not, Rem};
+use std::{
+    io::Read,
+    ops::{BitAnd, BitOr, BitXor, Not, Rem},
+};
 
 use crate::{
     engine_threading::*,
@@ -1363,6 +1366,136 @@ fn const_eval_intrinsic(
                 }),
             }
         }
+        Intrinsic::Transmute => {
+            let src_type = &intrinsic.type_arguments[0];
+            let src_ir_type = convert_resolved_type_id(
+                lookup.engines.te(),
+                lookup.engines.de(),
+                lookup.context,
+                src_type.type_id,
+                &src_type.span,
+            )
+            .unwrap();
+
+            let dst_type = &intrinsic.type_arguments[1];
+            let dst_ir_type = convert_resolved_type_id(
+                lookup.engines.te(),
+                lookup.engines.de(),
+                lookup.context,
+                dst_type.type_id,
+                &dst_type.span,
+            )
+            .unwrap();
+
+            // check IR sizes match
+            let src_ir_type_in_bytes = src_ir_type.size(lookup.context).in_bytes();
+            let dst_ir_type_in_bytes = dst_ir_type.size(lookup.context).in_bytes();
+            if src_ir_type_in_bytes != dst_ir_type_in_bytes {
+                return Err(ConstEvalError::CompileError);
+            }
+
+            fn append_bytes(
+                ctx: &Context<'_>,
+                bytes: &mut Vec<u8>,
+                t: &Type,
+                value: &ConstantValue,
+            ) -> Result<(), ConstEvalError> {
+                match t.get_content(ctx) {
+                    TypeContent::Array(item_type, size) => match value {
+                        ConstantValue::Array(items) => {
+                            assert!(*size as usize == items.len());
+                            for item in items {
+                                append_bytes(ctx, bytes, item_type, &item.value)?;
+                            }
+                        }
+                        _ => unreachable!(),
+                    },
+                    TypeContent::Uint(8) => match value {
+                        ConstantValue::Uint(v) => {
+                            bytes.extend((*v as u8).to_be_bytes());
+                        }
+                        _ => unreachable!(),
+                    },
+                    TypeContent::Uint(16) => match value {
+                        ConstantValue::Uint(v) => {
+                            bytes.extend([0u8, 0u8, 0u8, 0u8, 0u8, 0u8]);
+                            bytes.extend((*v as u16).to_be_bytes());
+                        }
+                        _ => unreachable!(),
+                    },
+                    TypeContent::Uint(32) => match value {
+                        ConstantValue::Uint(v) => {
+                            bytes.extend([0u8, 0u8, 0u8, 0u8]);
+                            bytes.extend((*v as u32).to_be_bytes());
+                        }
+                        _ => unreachable!(),
+                    },
+                    TypeContent::Uint(64) => match value {
+                        ConstantValue::Uint(v) => {
+                            bytes.extend((*v).to_be_bytes());
+                        }
+                        _ => unreachable!(),
+                    },
+                    _ => return Err(ConstEvalError::CompileError),
+                }
+                Ok(())
+            }
+
+            fn transmute_bytes(
+                ctx: &Context<'_>,
+                bytes: &mut std::io::Cursor<Vec<u8>>,
+                t: &Type,
+            ) -> Result<Constant, ConstEvalError> {
+                Ok(match t.get_content(ctx) {
+                    TypeContent::Uint(8) => {
+                        let mut buffer = [0u8];
+                        let _ = bytes.read_exact(&mut buffer);
+                        Constant {
+                            ty: Type::get_uint8(ctx),
+                            value: ConstantValue::Uint(buffer[0] as u64),
+                        }
+                    }
+                    TypeContent::Uint(16) => {
+                        let mut buffer = [0u8; 8]; // u16 = u64 at runtime
+                        let _ = bytes.read_exact(&mut buffer);
+                        let buffer = [buffer[6], buffer[7]];
+                        Constant {
+                            ty: Type::get_uint16(ctx),
+                            value: ConstantValue::Uint(u16::from_be_bytes(buffer) as u64),
+                        }
+                    }
+                    TypeContent::Uint(32) => {
+                        let mut buffer = [0u8; 8]; // u32 = u64 at runtime
+                        let _ = bytes.read_exact(&mut buffer);
+                        let buffer = [buffer[4], buffer[5], buffer[6], buffer[7]];
+                        Constant {
+                            ty: Type::get_uint32(ctx),
+                            value: ConstantValue::Uint(u32::from_be_bytes(buffer) as u64),
+                        }
+                    }
+                    TypeContent::Uint(64) => {
+                        let mut buffer = [0u8; 8];
+                        let _ = bytes.read_exact(&mut buffer);
+                        Constant {
+                            ty: Type::get_uint64(ctx),
+                            value: ConstantValue::Uint(u64::from_be_bytes(buffer)),
+                        }
+                    }
+                    _ => return Err(ConstEvalError::CompileError),
+                })
+            }
+
+            let mut runtime_bytes = vec![];
+            append_bytes(
+                lookup.context,
+                &mut runtime_bytes,
+                &src_ir_type,
+                &args[0].value,
+            )?;
+            let mut cursor = std::io::Cursor::new(runtime_bytes);
+            let c = transmute_bytes(lookup.context, &mut cursor, &dst_ir_type)?;
+            Ok(Some(c))
+        }
     }
 }
 

sway-core/src/ir_generation/function.rs

@@ -660,9 +660,13 @@ impl<'eng> FnCompiler<'eng> {
                     span_md_idx,
                 )
             }
-            ty::TyExpressionVariant::IntrinsicFunction(kind) => {
-                self.compile_intrinsic_function(context, md_mgr, kind, ast_expr.span.clone())
-            }
+            ty::TyExpressionVariant::IntrinsicFunction(kind) => self.compile_intrinsic_function(
+                context,
+                md_mgr,
+                kind,
+                ast_expr.span.clone(),
+                ast_expr.return_type,
+            ),
             ty::TyExpressionVariant::AbiName(_) => {
                 let val = Value::new_constant(context, Constant::new_unit(context));
                 Ok(TerminatorValue::new(val, context))
@@ -869,6 +873,7 @@ impl<'eng> FnCompiler<'eng> {
             span: _,
         }: &ty::TyIntrinsicFunctionKind,
         span: Span,
+        return_type: TypeId,
     ) -> Result<TerminatorValue, CompileError> {
         fn store_key_in_local_mem(
             compiler: &mut FnCompiler,
@@ -2174,9 +2179,61 @@ impl<'eng> FnCompiler<'eng> {
             }
             Intrinsic::Slice => self.compile_intrinsic_slice(arguments, context, md_mgr),
             Intrinsic::ElemAt => self.compile_intrinsic_elem_at(arguments, context, md_mgr),
+            Intrinsic::Transmute => {
+                self.compile_intrinsic_transmute(arguments, return_type, context, md_mgr, &span)
+            }
         }
     }
 
+    fn compile_intrinsic_transmute(
+        &mut self,
+        arguments: &[ty::TyExpression],
+        return_type: TypeId,
+        context: &mut Context,
+        md_mgr: &mut MetadataManager,
+        span: &Span,
+    ) -> Result<TerminatorValue, CompileError> {
+        assert!(arguments.len() == 1);
+
+        let te = self.engines.te();
+        let de = self.engines.de();
+
+        let return_type_ir_type = convert_resolved_type_id(te, de, context, return_type, span)?;
+        let return_type_ir_type_ptr = Type::new_ptr(context, return_type_ir_type);
+
+        let first_argument_expr = &arguments[0];
+        let first_argument_value = return_on_termination_or_extract!(
+            self.compile_expression_to_value(context, md_mgr, first_argument_expr)?
+        );
+        let first_argument_type = first_argument_value
+            .get_type(context)
+            .expect("transmute first argument type not found");
+        let first_argument_ptr = save_to_local_return_ptr(self, context, first_argument_value)?;
+
+        // check IR sizes match
+        let first_arg_size = first_argument_type.size(context).in_bytes();
+        let return_type_size = return_type_ir_type.size(context).in_bytes();
+        if first_arg_size != return_type_size {
+            return Err(CompileError::Internal(
+                "Types size do not match",
+                span.clone(),
+            ));
+        }
+
+        let u64 = Type::get_uint64(context);
+        let first_argument_ptr = self
+            .current_block
+            .append(context)
+            .ptr_to_int(first_argument_ptr, u64);
+        let first_argument_ptr = self
+            .current_block
+            .append(context)
+            .int_to_ptr(first_argument_ptr, return_type_ir_type_ptr);
+
+        let final_value = self.current_block.append(context).load(first_argument_ptr);
+        Ok(TerminatorValue::new(final_value, context))
+    }
+
     fn ptr_to_first_element(
         &mut self,
         context: &mut Context,

sway-core/src/semantic_analysis/ast_node/expression/intrinsic_function.rs

@@ -106,8 +106,118 @@ impl ty::TyIntrinsicFunctionKind {
                 type_check_slice(handler, ctx, kind, arguments, type_arguments, span)
             }
             Intrinsic::ElemAt => type_check_elem_at(arguments, handler, kind, span, ctx),
+            Intrinsic::Transmute => {
+                type_check_transmute(arguments, handler, kind, type_arguments, span, ctx)
+            }
+        }
+    }
+}
+
+fn type_check_transmute(
+    arguments: &[Expression],
+    handler: &Handler,
+    kind: Intrinsic,
+    type_arguments: &[TypeArgument],
+    span: Span,
+    mut ctx: TypeCheckContext,
+) -> Result<(TyIntrinsicFunctionKind, TypeId), ErrorEmitted> {
+    if arguments.len() != 1 {
+        return Err(handler.emit_err(CompileError::IntrinsicIncorrectNumArgs {
+            name: kind.to_string(),
+            expected: 1,
+            span,
+        }));
+    }
+
+    let engines = ctx.engines();
+
+    // Both type arguments needs to be explicitly defined
+    if type_arguments.len() != 2 {
+        return Err(handler.emit_err(CompileError::IntrinsicIncorrectNumTArgs {
+            name: kind.to_string(),
+            expected: 2,
+            span,
+        }));
+    }
+
+    let src_type = ctx
+        .resolve_type(
+            handler,
+            type_arguments[0].type_id,
+            &type_arguments[0].span,
+            EnforceTypeArguments::Yes,
+            None,
+        )
+        .unwrap_or_else(|err| engines.te().id_of_error_recovery(err));
+    let return_type = ctx
+        .resolve_type(
+            handler,
+            type_arguments[1].type_id,
+            &type_arguments[1].span,
+            EnforceTypeArguments::Yes,
+            None,
+        )
+        .unwrap_or_else(|err| engines.te().id_of_error_recovery(err));
+
+    // Forbid ref and ptr types
+    fn forbid_ref_ptr_types(
+        engines: &Engines,
+        handler: &Handler,
+        t: TypeId,
+        span: &Span,
+    ) -> Result<(), ErrorEmitted> {
+        let types = t.extract_any_including_self(
+            engines,
+            &|t| {
+                matches!(
+                    t,
+                    TypeInfo::StringSlice
+                        | TypeInfo::RawUntypedPtr
+                        | TypeInfo::RawUntypedSlice
+                        | TypeInfo::Ptr(_)
+                        | TypeInfo::Slice(_)
+                        | TypeInfo::Ref { .. }
+                )
+            },
+            vec![],
+            0,
+        );
+        if !types.is_empty() {
+            Err(handler.emit_err(CompileError::TypeNotAllowed {
+                reason: sway_error::error::TypeNotAllowedReason::NotAllowedInTransmute,
+                span: span.clone(),
+            }))
+        } else {
+            Ok(())
         }
     }
+
+    forbid_ref_ptr_types(engines, handler, src_type, &type_arguments[0].span)?;
+    forbid_ref_ptr_types(engines, handler, return_type, &type_arguments[1].span)?;
+
+    // check first argument
+    let arg_type = engines.te().get(src_type);
+    let first_argument_typed_expr = {
+        let ctx = ctx
+            .by_ref()
+            .with_help_text("")
+            .with_type_annotation(engines.te().insert(
+                engines,
+                (*arg_type).clone(),
+                type_arguments[0].span.source_id(),
+            ));
+        ty::TyExpression::type_check(handler, ctx, &arguments[0]).unwrap()
+    };
+
+    Ok((
+        TyIntrinsicFunctionKind {
+            kind,
+            arguments: vec![first_argument_typed_expr],
+            type_arguments: type_arguments.to_vec(),
+            span,
+        },
+        return_type,
+    ))
 }
 
 fn type_check_elem_at(

sway-core/src/semantic_analysis/cei_pattern_analysis.rs

@@ -649,7 +649,8 @@ fn effects_of_intrinsic(intr: &sway_ast::Intrinsic) -> HashSet<Effect> {
         | EncodeBufferAppend
         | EncodeBufferAsRawSlice
         | Slice
-        | ElemAt => HashSet::new(),
+        | ElemAt
+        | Transmute => HashSet::new(),
     }
 }
 

sway-error/src/error.rs

@@ -2812,6 +2812,9 @@ pub enum TypeNotAllowedReason {
 
     #[error("slices or types containing slices on `const` are not allowed.")]
     SliceInConst,
+
+    #[error("references, pointers, slices, string slices or types containing any of these are not allowed.")]
+    NotAllowedInTransmute,
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]

test/src/e2e_vm_tests/test_programs/should_fail/language/intrinsics/transmute/.gitignore

@@ -0,0 +1,2 @@
+out
+target