Translate builtin_assume and unaligned SIMD intrinsics

Unaligned vector types such as `__m128_u` or `__256_u` not not have
any equivalents in Rust so we translate them to their aligned equivalents.
This is unsound so we emit warning that the program may be mistranspiled.

c2rust-transpile/src/translator/builtins.rs

@@ -613,6 +613,9 @@ impl<'c> Translation<'c> {
                     )
                 })
             }
+
+            // TODO: provide proper implementation, this is just to get stuff building
+            "__builtin_assume" =>  Ok(self.convert_expr(ctx.used(), args[0])?),
             // There's currently no way to replicate this functionality in Rust, so we just
             // pass the ptr input param in its place.
             "__builtin_assume_aligned" => Ok(self.convert_expr(ctx.used(), args[0])?),

c2rust-transpile/src/translator/simd.rs

@@ -91,7 +91,9 @@ impl<'c> Translation<'c> {
     pub fn import_simd_typedef(&self, name: &str) -> TranslationResult<bool> {
         Ok(match name {
             // Public API SIMD typedefs:
-            "__m128i" | "__m128" | "__m128d" | "__m64" | "__m256" | "__m256d" | "__m256i" => {
+            "__m64" | "__m128i" | "__m128i_u" | "__m128" | "__m128d" | "__m128_u" | "__m256"
+            | "__m256d" | "__m256_u" | "__m256i" | "__m256i_u" | "__m512 " | "__m512d"
+            | "__m512i" | "__m512i_u" | "__m512_u" => {
                 // __m64 and MMX support were removed from upstream Rust.
                 // See https://github.com/immunant/c2rust/issues/369
                 if name == "__m64" {
@@ -100,6 +102,21 @@ impl<'c> Translation<'c> {
                     ).into());
                 }
 
+                // Drop the `_u` suffix for unaligned SIMD types as they have
+                // no equivalents in Rust. Warn the user about possible probems.
+                let name = if name.ends_with("_u") {
+                    warn!(
+                        "Unaligned SIMD type {} has no equivalent in Rust. \
+                           Emitting {} instead. This likely means the potential \
+                           for miscompilation has been introduced.",
+                        name,
+                        &name[..name.len() - 2]
+                    );
+                    &name[..name.len() - 2]
+                } else {
+                    name
+                };
+
                 self.with_cur_file_item_store(|item_store| {
                     add_arch_use(item_store, "x86", name);
                     add_arch_use(item_store, "x86_64", name);

c2rust-transpile/src/translator/structs.rs

@@ -377,7 +377,33 @@ impl<'a> Translation<'a> {
 
                     field_entries.push(field);
                 }
-                FieldType::Regular { field, .. } => field_entries.push(*field),
+                FieldType::Regular {
+                    mut field, name, ..
+                } => {
+                    if let crate::translator::Type::Path(segments, ..) = &field.ty {
+                        for seg in &segments.path.segments {
+                            let tynam = seg.ident.to_string();
+                            match tynam.as_str() {
+                                "__m128i_u" | "__m128_u" | "__m256i_u" | "__m256_u"
+                                | "__m512_u" | "__m512i_u" => {
+                                    // TODO: We might already have emitted a warning in `import_simd_typedef`,
+                                    // is it always safe to skip the warning here?
+                                    log::warn!("Unaligned SIMD type {} in field {} has no equivalent in Rust. \
+                                          Emitting {} instead. This likely means the potential \
+                                          for miscompilation has been introduced.",
+                                          tynam,
+                                          name,
+                                          &tynam[..tynam.len() - 2],
+                                    );
+                                    field.ty = *mk().ident_ty(&tynam[..tynam.len() - 2]);
+                                    break;
+                                }
+                                _ => {}
+                            }
+                        }
+                    }
+                    field_entries.push(*field)
+                }
             }
         }
         Ok((field_entries, contains_va_list))