Auto merge of #136974 - m-ou-se:fmt-options-64-bit, r=<try>

Reduce FormattingOptions to 64 bits

This reduces FormattingOptions from 6-7 machine words (384 bits on 64-bit platforms, 224 bits on 32-bit platforms) to just 64 bits (a single register on 64-bit platforms).

This PR includes #136932, which reduces the width and precision options to 16 bits, to make it all fit.

Before:

```rust
pub struct FormattingOptions {
    flags: u32, // only 6 bits used
    fill: char,
    align: Option<Alignment>,
    width: Option<usize>,
    precision: Option<usize>,
}
```

After:

```rust
pub struct FormattingOptions {
    /// Bits:
    ///  - 0: `+` flag [rt::Flag::SignPlus]
    ///  - 1: `-` flag [rt::Flag::SignMinus]
    ///  - 2: `#` flag [rt::Flag::Alternate]
    ///  - 3: `0` flag [rt::Flag::SignAwareZeroPad]
    ///  - 4: `x?` flag [rt::Flag::DebugLowerHex]
    ///  - 5: `X?` flag [rt::Flag::DebugUpperHex]
    ///  - 6-7: Alignment (0: Left, 1: Right, 2: Center, 3: Unknown)
    ///  - 8: Width flag (if set, the width field below is used)
    ///  - 9: Precision flag (if set, the precision field below is used)
    ///  - 10: unused
    ///  - 11-31: fill character (21 bits, a full `char`)
    flags: u32,
    /// Width if width flag above is set. Otherwise, always 0.
    width: u16,
    /// Precision if precision flag above is set. Otherwise, always 0.
    precision: u16,
}
```

compiler/rustc_ast/src/format.rs

@@ -266,7 +266,7 @@ pub enum FormatAlignment {
 #[derive(Clone, Encodable, Decodable, Debug, PartialEq, Eq)]
 pub enum FormatCount {
     /// `{:5}` or `{:.5}`
-    Literal(usize),
+    Literal(u16),
     /// `{:.*}`, `{:.5$}`, or `{:a$}`, etc.
     Argument(FormatArgPosition),
 }

compiler/rustc_ast_lowering/src/expr.rs

@@ -2151,8 +2151,14 @@ impl<'hir> LoweringContext<'_, 'hir> {
         self.expr(sp, hir::ExprKind::Lit(lit))
     }
 
-    pub(super) fn expr_char(&mut self, sp: Span, value: char) -> hir::Expr<'hir> {
-        let lit = self.arena.alloc(hir::Lit { span: sp, node: ast::LitKind::Char(value) });
+    pub(super) fn expr_u16(&mut self, sp: Span, value: u16) -> hir::Expr<'hir> {
+        let lit = self.arena.alloc(hir::Lit {
+            span: sp,
+            node: ast::LitKind::Int(
+                u128::from(value).into(),
+                ast::LitIntType::Unsigned(ast::UintTy::U16),
+            ),
+        });
         self.expr(sp, hir::ExprKind::Lit(lit))
     }
 

compiler/rustc_ast_lowering/src/format.rs

@@ -292,7 +292,7 @@ fn make_count<'hir>(
                 hir::LangItem::FormatCount,
                 sym::Is,
             ));
-            let value = ctx.arena.alloc_from_iter([ctx.expr_usize(sp, *n)]);
+            let value = ctx.arena.alloc_from_iter([ctx.expr_u16(sp, *n)]);
             ctx.expr_call_mut(sp, count_is, value)
         }
         Some(FormatCount::Argument(arg)) => {
@@ -361,24 +361,25 @@ fn make_format_spec<'hir>(
         zero_pad,
         debug_hex,
     } = &placeholder.format_options;
-    let fill = ctx.expr_char(sp, fill.unwrap_or(' '));
-    let align = ctx.expr_lang_item_type_relative(
-        sp,
-        hir::LangItem::FormatAlignment,
-        match alignment {
-            Some(FormatAlignment::Left) => sym::Left,
-            Some(FormatAlignment::Right) => sym::Right,
-            Some(FormatAlignment::Center) => sym::Center,
-            None => sym::Unknown,
-        },
-    );
-    // This needs to match `Flag` in library/core/src/fmt/rt.rs.
+    let fill = fill.unwrap_or(' ');
+    // These need to match the constants in library/core/src/fmt/rt.rs.
+    let align = match alignment {
+        Some(FormatAlignment::Left) => 0,
+        Some(FormatAlignment::Right) => 1,
+        Some(FormatAlignment::Center) => 2,
+        None => 3,
+    };
+    // This needs to match the constants in library/core/src/fmt/rt.rs.
     let flags: u32 = ((sign == Some(FormatSign::Plus)) as u32)
         | ((sign == Some(FormatSign::Minus)) as u32) << 1
         | (alternate as u32) << 2
         | (zero_pad as u32) << 3
         | ((debug_hex == Some(FormatDebugHex::Lower)) as u32) << 4
-        | ((debug_hex == Some(FormatDebugHex::Upper)) as u32) << 5;
+        | ((debug_hex == Some(FormatDebugHex::Upper)) as u32) << 5
+        | align << 6
+        | (width.is_some() as u32) << 8
+        | (precision.is_some() as u32) << 9
+        | (fill as u32) << 11;
     let flags = ctx.expr_u32(sp, flags);
     let precision = make_count(ctx, sp, precision, argmap);
     let width = make_count(ctx, sp, width, argmap);
@@ -387,7 +388,7 @@ fn make_format_spec<'hir>(
         hir::LangItem::FormatPlaceholder,
         sym::new,
     ));
-    let args = ctx.arena.alloc_from_iter([position, fill, align, flags, precision, width]);
+    let args = ctx.arena.alloc_from_iter([position, flags, precision, width]);
     ctx.expr_call_mut(sp, format_placeholder_new, args)
 }
 

compiler/rustc_hir/src/lang_items.rs

@@ -321,7 +321,6 @@ language_item_table! {
     BeginPanic,              sym::begin_panic,         begin_panic_fn,             Target::Fn,             GenericRequirement::None;
 
     // Lang items needed for `format_args!()`.
-    FormatAlignment,         sym::format_alignment,    format_alignment,           Target::Enum,           GenericRequirement::None;
     FormatArgument,          sym::format_argument,     format_argument,            Target::Struct,         GenericRequirement::None;
     FormatArguments,         sym::format_arguments,    format_arguments,           Target::Struct,         GenericRequirement::None;
     FormatCount,             sym::format_count,        format_count,               Target::Enum,           GenericRequirement::None;

compiler/rustc_parse_format/src/lib.rs

@@ -190,7 +190,7 @@ pub enum DebugHex {
 #[derive(Copy, Clone, Debug, PartialEq)]
 pub enum Count<'a> {
     /// The count is specified explicitly.
-    CountIs(usize),
+    CountIs(u16),
     /// The count is specified by the argument with the given name.
     CountIsName(&'a str, InnerSpan),
     /// The count is specified by the argument at the given index.
@@ -565,7 +565,7 @@ impl<'a> Parser<'a> {
     /// consuming a macro argument, `None` if it's the case.
     fn position(&mut self) -> Option<Position<'a>> {
         if let Some(i) = self.integer() {
-            Some(ArgumentIs(i))
+            Some(ArgumentIs(i.into()))
         } else {
             match self.cur.peek() {
                 Some(&(lo, c)) if rustc_lexer::is_id_start(c) => {
@@ -771,7 +771,7 @@ impl<'a> Parser<'a> {
     /// width.
     fn count(&mut self, start: usize) -> Count<'a> {
         if let Some(i) = self.integer() {
-            if self.consume('$') { CountIsParam(i) } else { CountIs(i) }
+            if self.consume('$') { CountIsParam(i.into()) } else { CountIs(i) }
         } else {
             let tmp = self.cur.clone();
             let word = self.word();
@@ -822,15 +822,15 @@ impl<'a> Parser<'a> {
         word
     }
 
-    fn integer(&mut self) -> Option<usize> {
-        let mut cur: usize = 0;
+    fn integer(&mut self) -> Option<u16> {
+        let mut cur: u16 = 0;
         let mut found = false;
         let mut overflow = false;
         let start = self.current_pos();
         while let Some(&(_, c)) = self.cur.peek() {
             if let Some(i) = c.to_digit(10) {
                 let (tmp, mul_overflow) = cur.overflowing_mul(10);
-                let (tmp, add_overflow) = tmp.overflowing_add(i as usize);
+                let (tmp, add_overflow) = tmp.overflowing_add(i as u16);
                 if mul_overflow || add_overflow {
                     overflow = true;
                 }
@@ -847,11 +847,11 @@ impl<'a> Parser<'a> {
             let overflowed_int = &self.input[start..end];
             self.err(
                 format!(
-                    "integer `{}` does not fit into the type `usize` whose range is `0..={}`",
+                    "integer `{}` does not fit into the type `u16` whose range is `0..={}`",
                     overflowed_int,
-                    usize::MAX
+                    u16::MAX
                 ),
-                "integer out of range for `usize`",
+                "integer out of range for `u16`",
                 self.span(start, end),
             );
         }

compiler/rustc_span/src/symbol.rs

@@ -978,7 +978,6 @@ symbols! {
         forbid,
         forget,
         format,
-        format_alignment,
         format_args,
         format_args_capture,
         format_args_macro,
@@ -1003,6 +1002,7 @@ symbols! {
         from_residual,
         from_size_align_unchecked,
         from_str_method,
+        from_u16,
         from_usize,
         from_yeet,
         fs_create_dir,

library/core/src/fmt/float.rs

@@ -29,7 +29,7 @@ fn float_to_decimal_common_exact<T>(
     fmt: &mut Formatter<'_>,
     num: &T,
     sign: flt2dec::Sign,
-    precision: usize,
+    precision: u16,
 ) -> Result
 where
     T: flt2dec::DecodableFloat,
@@ -40,7 +40,7 @@ where
         flt2dec::strategy::grisu::format_exact,
         *num,
         sign,
-        precision,
+        precision.into(),
         &mut buf,
         &mut parts,
     );
@@ -55,7 +55,7 @@ fn float_to_decimal_common_shortest<T>(
     fmt: &mut Formatter<'_>,
     num: &T,
     sign: flt2dec::Sign,
-    precision: usize,
+    precision: u16,
 ) -> Result
 where
     T: flt2dec::DecodableFloat,
@@ -68,7 +68,7 @@ where
         flt2dec::strategy::grisu::format_shortest,
         *num,
         sign,
-        precision,
+        precision.into(),
         &mut buf,
         &mut parts,
     );
@@ -86,7 +86,7 @@ where
         true => flt2dec::Sign::MinusPlus,
     };
 
-    if let Some(precision) = fmt.options.precision {
+    if let Some(precision) = fmt.options.get_precision() {
         float_to_decimal_common_exact(fmt, num, sign, precision)
     } else {
         let min_precision = 0;
@@ -101,7 +101,7 @@ fn float_to_exponential_common_exact<T>(
     fmt: &mut Formatter<'_>,
     num: &T,
     sign: flt2dec::Sign,
-    precision: usize,
+    precision: u16,
     upper: bool,
 ) -> Result
 where
@@ -113,7 +113,7 @@ where
         flt2dec::strategy::grisu::format_exact,
         *num,
         sign,
-        precision,
+        precision.into(),
         upper,
         &mut buf,
         &mut parts,
@@ -162,7 +162,7 @@ where
         true => flt2dec::Sign::MinusPlus,
     };
 
-    if let Some(precision) = fmt.options.precision {
+    if let Some(precision) = fmt.options.get_precision() {
         // 1 integral digit + `precision` fractional digits = `precision + 1` total digits
         float_to_exponential_common_exact(fmt, num, sign, precision + 1, upper)
     } else {
@@ -180,7 +180,7 @@ where
         true => flt2dec::Sign::MinusPlus,
     };
 
-    if let Some(precision) = fmt.options.precision {
+    if let Some(precision) = fmt.options.get_precision() {
         // this behavior of {:.PREC?} predates exponential formatting for {:?}
         float_to_decimal_common_exact(fmt, num, sign, precision)
     } else {