Auto merge of #122671 - Mark-Simulacrum:const-panic-msg, r=<try>

Codegen const panic messages as function calls

This skips emitting extra arguments at every callsite (of which there can be many). We could handwrite these functions if the approach here proves fairly expensive at compile-time.

r? `@Mark-Simulacrum` (for perf, for now)

Author: bors

compiler/rustc_codegen_ssa/src/mir/block.rs

@@ -651,10 +651,8 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 (LangItem::PanicMisalignedPointerDereference, vec![required, found, location])
             }
             _ => {
-                let msg = bx.const_str(msg.description());
-                // It's `pub fn panic(expr: &str)`, with the wide reference being passed
-                // as two arguments, and `#[track_caller]` adds an implicit third argument.
-                (LangItem::Panic, vec![msg.0, msg.1, location])
+                // It's `pub fn panic_...()` and `#[track_caller]` adds an implicit argument.
+                (msg.description(), vec![location])
             }
         };
 

compiler/rustc_hir/src/lang_items.rs

@@ -246,6 +246,25 @@ language_item_table! {
     PanicImpl,               sym::panic_impl,          panic_impl,                 Target::Fn,             GenericRequirement::None;
     PanicCannotUnwind,       sym::panic_cannot_unwind, panic_cannot_unwind,        Target::Fn,             GenericRequirement::Exact(0);
     PanicInCleanup,          sym::panic_in_cleanup,    panic_in_cleanup,           Target::Fn,             GenericRequirement::Exact(0);
+    /// Constant panic messages, used for codegen of MIR asserts.
+    PanicAddOverflow,        sym::panic_const_add_overflow, panic_const_add_overflow, Target::Fn, GenericRequirement::None;
+    PanicSubOverflow,        sym::panic_const_sub_overflow, panic_const_sub_overflow, Target::Fn, GenericRequirement::None;
+    PanicMulOverflow,        sym::panic_const_mul_overflow, panic_const_mul_overflow, Target::Fn, GenericRequirement::None;
+    PanicDivOverflow,        sym::panic_const_div_overflow, panic_const_div_overflow, Target::Fn, GenericRequirement::None;
+    PanicRemOverflow,        sym::panic_const_rem_overflow, panic_const_rem_overflow, Target::Fn, GenericRequirement::None;
+    PanicNegOverflow,        sym::panic_const_neg_overflow, panic_const_neg_overflow, Target::Fn, GenericRequirement::None;
+    PanicShrOverflow,        sym::panic_const_shr_overflow, panic_const_shr_overflow, Target::Fn, GenericRequirement::None;
+    PanicShlOverflow,        sym::panic_const_shl_overflow, panic_const_shl_overflow, Target::Fn, GenericRequirement::None;
+    PanicDivZero,            sym::panic_const_div_by_zero, panic_const_div_by_zero, Target::Fn, GenericRequirement::None;
+    PanicRemZero,            sym::panic_const_rem_by_zero, panic_const_rem_by_zero, Target::Fn, GenericRequirement::None;
+    PanicCoroutineResumed, sym::panic_const_coroutine_resumed, panic_const_coroutine_resumed, Target::Fn, GenericRequirement::None;
+    PanicAsyncFnResumed, sym::panic_const_async_fn_resumed, panic_const_async_fn_resumed, Target::Fn, GenericRequirement::None;
+    PanicAsyncGenFnResumed, sym::panic_const_async_gen_fn_resumed, panic_const_async_gen_fn_resumed, Target::Fn, GenericRequirement::None;
+    PanicGenFnNone, sym::panic_const_gen_fn_none, panic_const_gen_fn_none, Target::Fn, GenericRequirement::None;
+    PanicCoroutineResumedPanic, sym::panic_const_coroutine_resumed_panic, panic_const_coroutine_resumed_panic, Target::Fn, GenericRequirement::None;
+    PanicAsyncFnResumedPanic, sym::panic_const_async_fn_resumed_panic, panic_const_async_fn_resumed_panic, Target::Fn, GenericRequirement::None;
+    PanicAsyncGenFnResumedPanic, sym::panic_const_async_gen_fn_resumed_panic, panic_const_async_gen_fn_resumed_panic, Target::Fn, GenericRequirement::None;
+    PanicGenFnNonePanic, sym::panic_const_gen_fn_none_panic, panic_const_gen_fn_none_panic, Target::Fn, GenericRequirement::None;
     /// libstd panic entry point. Necessary for const eval to be able to catch it
     BeginPanic,              sym::begin_panic,         begin_panic_fn,             Target::Fn,             GenericRequirement::None;
 

compiler/rustc_middle/src/mir/terminator.rs

@@ -149,44 +149,45 @@ impl<O> AssertKind<O> {
         matches!(self, OverflowNeg(..) | Overflow(Add | Sub | Mul | Shl | Shr, ..))
     }
 
-    /// Get the message that is printed at runtime when this assertion fails.
+    /// Get the lang item that is invoked to print a static message when this assert fires.
     ///
     /// The caller is expected to handle `BoundsCheck` and `MisalignedPointerDereference` by
     /// invoking the appropriate lang item (panic_bounds_check/panic_misaligned_pointer_dereference)
-    /// instead of printing a static message.
-    pub fn description(&self) -> &'static str {
+    /// instead of printing a static message. Those have dynamic arguments that aren't present for
+    /// the rest of the messages here.
+    pub fn description(&self) -> LangItem {
         use AssertKind::*;
         match self {
-            Overflow(BinOp::Add, _, _) => "attempt to add with overflow",
-            Overflow(BinOp::Sub, _, _) => "attempt to subtract with overflow",
-            Overflow(BinOp::Mul, _, _) => "attempt to multiply with overflow",
-            Overflow(BinOp::Div, _, _) => "attempt to divide with overflow",
-            Overflow(BinOp::Rem, _, _) => "attempt to calculate the remainder with overflow",
-            OverflowNeg(_) => "attempt to negate with overflow",
-            Overflow(BinOp::Shr, _, _) => "attempt to shift right with overflow",
-            Overflow(BinOp::Shl, _, _) => "attempt to shift left with overflow",
+            Overflow(BinOp::Add, _, _) => LangItem::PanicAddOverflow,
+            Overflow(BinOp::Sub, _, _) => LangItem::PanicSubOverflow,
+            Overflow(BinOp::Mul, _, _) => LangItem::PanicMulOverflow,
+            Overflow(BinOp::Div, _, _) => LangItem::PanicDivOverflow,
+            Overflow(BinOp::Rem, _, _) => LangItem::PanicRemOverflow,
+            OverflowNeg(_) => LangItem::PanicNegOverflow,
+            Overflow(BinOp::Shr, _, _) => LangItem::PanicShrOverflow,
+            Overflow(BinOp::Shl, _, _) => LangItem::PanicShlOverflow,
             Overflow(op, _, _) => bug!("{:?} cannot overflow", op),
-            DivisionByZero(_) => "attempt to divide by zero",
-            RemainderByZero(_) => "attempt to calculate the remainder with a divisor of zero",
-            ResumedAfterReturn(CoroutineKind::Coroutine(_)) => "coroutine resumed after completion",
+            DivisionByZero(_) => LangItem::PanicDivZero,
+            RemainderByZero(_) => LangItem::PanicRemZero,
+            ResumedAfterReturn(CoroutineKind::Coroutine(_)) => LangItem::PanicCoroutineResumed,
             ResumedAfterReturn(CoroutineKind::Desugared(CoroutineDesugaring::Async, _)) => {
-                "`async fn` resumed after completion"
+                LangItem::PanicAsyncFnResumed
             }
             ResumedAfterReturn(CoroutineKind::Desugared(CoroutineDesugaring::AsyncGen, _)) => {
-                "`async gen fn` resumed after completion"
+                LangItem::PanicAsyncGenFnResumed
             }
             ResumedAfterReturn(CoroutineKind::Desugared(CoroutineDesugaring::Gen, _)) => {
-                "`gen fn` should just keep returning `None` after completion"
+                LangItem::PanicGenFnNone
             }
-            ResumedAfterPanic(CoroutineKind::Coroutine(_)) => "coroutine resumed after panicking",
+            ResumedAfterPanic(CoroutineKind::Coroutine(_)) => LangItem::PanicCoroutineResumedPanic,
             ResumedAfterPanic(CoroutineKind::Desugared(CoroutineDesugaring::Async, _)) => {
-                "`async fn` resumed after panicking"
+                LangItem::PanicAsyncFnResumedPanic
             }
             ResumedAfterPanic(CoroutineKind::Desugared(CoroutineDesugaring::AsyncGen, _)) => {
-                "`async gen fn` resumed after panicking"
+                LangItem::PanicAsyncGenFnResumedPanic
             }
             ResumedAfterPanic(CoroutineKind::Desugared(CoroutineDesugaring::Gen, _)) => {
-                "`gen fn` should just keep returning `None` after panicking"
+                LangItem::PanicGenFnNonePanic
             }
 
             BoundsCheck { .. } | MisalignedPointerDereference { .. } => {
@@ -246,13 +247,37 @@ impl<O> AssertKind<O> {
             Overflow(BinOp::Shl, _, r) => {
                 write!(f, "\"attempt to shift left by `{{}}`, which would overflow\", {r:?}")
             }
+            Overflow(op, _, _) => bug!("{:?} cannot overflow", op),
             MisalignedPointerDereference { required, found } => {
                 write!(
                     f,
                     "\"misaligned pointer dereference: address must be a multiple of {{}} but is {{}}\", {required:?}, {found:?}"
                 )
             }
-            _ => write!(f, "\"{}\"", self.description()),
+            ResumedAfterReturn(CoroutineKind::Coroutine(_)) => {
+                write!(f, "\"coroutine resumed after completion\"")
+            }
+            ResumedAfterReturn(CoroutineKind::Desugared(CoroutineDesugaring::Async, _)) => {
+                write!(f, "\"`async fn` resumed after completion\"")
+            }
+            ResumedAfterReturn(CoroutineKind::Desugared(CoroutineDesugaring::AsyncGen, _)) => {
+                write!(f, "\"`async gen fn` resumed after completion\"")
+            }
+            ResumedAfterReturn(CoroutineKind::Desugared(CoroutineDesugaring::Gen, _)) => {
+                write!(f, "\"`gen fn` should just keep returning `None` after completion\"")
+            }
+            ResumedAfterPanic(CoroutineKind::Coroutine(_)) => {
+                write!(f, "\"coroutine resumed after panicking\"")
+            }
+            ResumedAfterPanic(CoroutineKind::Desugared(CoroutineDesugaring::Async, _)) => {
+                write!(f, "\"`async fn` resumed after panicking\"")
+            }
+            ResumedAfterPanic(CoroutineKind::Desugared(CoroutineDesugaring::AsyncGen, _)) => {
+                write!(f, "\"`async gen fn` resumed after panicking\"")
+            }
+            ResumedAfterPanic(CoroutineKind::Desugared(CoroutineDesugaring::Gen, _)) => {
+                write!(f, "\"`gen fn` should just keep returning `None` after panicking\"")
+            }
         }
     }
 

compiler/rustc_monomorphize/src/collector.rs

@@ -886,16 +886,17 @@ impl<'a, 'tcx> MirVisitor<'tcx> for MirUsedCollector<'a, 'tcx> {
                     }
                 }
             }
-            mir::TerminatorKind::Assert { ref msg, .. } => {
-                let lang_item = match &**msg {
-                    mir::AssertKind::BoundsCheck { .. } => LangItem::PanicBoundsCheck,
-                    mir::AssertKind::MisalignedPointerDereference { .. } => {
-                        LangItem::PanicMisalignedPointerDereference
-                    }
-                    _ => LangItem::Panic,
-                };
-                push_mono_lang_item(self, lang_item);
-            }
+            mir::TerminatorKind::Assert { ref msg, .. } => match &**msg {
+                mir::AssertKind::BoundsCheck { .. } => {
+                    push_mono_lang_item(self, LangItem::PanicBoundsCheck);
+                }
+                mir::AssertKind::MisalignedPointerDereference { .. } => {
+                    push_mono_lang_item(self, LangItem::PanicMisalignedPointerDereference);
+                }
+                _ => {
+                    push_mono_lang_item(self, msg.description());
+                }
+            },
             mir::TerminatorKind::UnwindTerminate(reason) => {
                 push_mono_lang_item(self, reason.lang_item());
             }

compiler/rustc_span/src/symbol.rs

@@ -1297,6 +1297,24 @@ symbols! {
         panic_abort,
         panic_bounds_check,
         panic_cannot_unwind,
+        panic_const_add_overflow,
+        panic_const_async_fn_resumed,
+        panic_const_async_fn_resumed_panic,
+        panic_const_async_gen_fn_resumed,
+        panic_const_async_gen_fn_resumed_panic,
+        panic_const_coroutine_resumed,
+        panic_const_coroutine_resumed_panic,
+        panic_const_div_by_zero,
+        panic_const_div_overflow,
+        panic_const_gen_fn_none,
+        panic_const_gen_fn_none_panic,
+        panic_const_mul_overflow,
+        panic_const_neg_overflow,
+        panic_const_rem_by_zero,
+        panic_const_rem_overflow,
+        panic_const_shl_overflow,
+        panic_const_shr_overflow,
+        panic_const_sub_overflow,
         panic_fmt,
         panic_handler,
         panic_impl,

library/core/src/panicking.rs

@@ -145,6 +145,57 @@ pub const fn panic(expr: &'static str) -> ! {
     panic_fmt(fmt::Arguments::new_const(&[expr]));
 }
 
+macro_rules! panic_const {
+    ($($lang:ident = $message:expr,)+) => {
+        #[cfg(not(bootstrap))]
+        pub mod panic_const {
+            use super::*;
+
+            $(
+                /// This is a panic called with a message that's a result of a MIR-produced Assert.
+                //
+                // never inline unless panic_immediate_abort to avoid code
+                // bloat at the call sites as much as possible
+                #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]
+                #[cfg_attr(feature = "panic_immediate_abort", inline)]
+                #[track_caller]
+                #[rustc_const_unstable(feature = "panic_internals", issue = "none")]
+                #[lang = stringify!($lang)] // needed by codegen for panic on overflow and other `Assert` MIR terminators
+                pub const fn $lang() -> ! {
+                    // Use Arguments::new_v1 instead of format_args!("{expr}") to potentially
+                    // reduce size overhead. The format_args! macro uses str's Display trait to
+                    // write expr, which calls Formatter::pad, which must accommodate string
+                    // truncation and padding (even though none is used here). Using
+                    // Arguments::new_v1 may allow the compiler to omit Formatter::pad from the
+                    // output binary, saving up to a few kilobytes.
+                    panic_fmt(fmt::Arguments::new_const(&[$message]));
+                }
+            )+
+        }
+    }
+}
+
+panic_const! {
+    panic_const_add_overflow = "attempt to add with overflow",
+    panic_const_sub_overflow = "attempt to subtract with overflow",
+    panic_const_mul_overflow = "attempt to multiply with overflow",
+    panic_const_div_overflow = "attempt to divide with overflow",
+    panic_const_rem_overflow = "attempt to calculate the remainder with overflow",
+    panic_const_neg_overflow = "attempt to negate with overflow",
+    panic_const_shr_overflow = "attempt to shift right with overflow",
+    panic_const_shl_overflow = "attempt to shift left with overflow",
+    panic_const_div_by_zero = "attempt to divide by zero",
+    panic_const_rem_by_zero = "attempt to calculate the remainder with a divisor of zero",
+    panic_const_coroutine_resumed = "coroutine resumed after completion",
+    panic_const_async_fn_resumed = "`async fn` resumed after completion",
+    panic_const_async_gen_fn_resumed = "`async gen fn` resumed after completion",
+    panic_const_gen_fn_none = "`gen fn` should just keep returning `None` after completion",
+    panic_const_coroutine_resumed_panic = "coroutine resumed after panicking",
+    panic_const_async_fn_resumed_panic = "`async fn` resumed after panicking",
+    panic_const_async_gen_fn_resumed_panic = "`async gen fn` resumed after panicking",
+    panic_const_gen_fn_none_panic = "`gen fn` should just keep returning `None` after panicking",
+}
+
 /// Like `panic`, but without unwinding and track_caller to reduce the impact on codesize on the caller.
 /// If you want `#[track_caller]` for nicer errors, call `panic_nounwind_fmt` directly.
 #[cfg_attr(not(feature = "panic_immediate_abort"), inline(never), cold)]