Auto merge of #122671 - Mark-Simulacrum:const-panic-msg, r=Nilstrieb

Codegen const panic messages as function calls

This skips emitting extra arguments at every callsite (of which there
can be many). For a librustc_driver build with overflow checks enabled,
this cuts 0.7MB from the resulting shared library (see [perf]).

A sample improvement from nightly:

```
        leaq    str.0(%rip), %rdi
        leaq    .Lalloc_d6aeb8e2aa19de39a7f0e861c998af13(%rip), %rdx
        movl    $25, %esi
        callq   *_ZN4core9panicking5panic17h17cabb89c5bcc999E@GOTPCREL(%rip)
```

to this PR:

```
        leaq    .Lalloc_d6aeb8e2aa19de39a7f0e861c998af13(%rip), %rdi
        callq   *_RNvNtNtCsduqIKoij8JB_4core9panicking11panic_const23panic_const_div_by_zero@GOTPCREL(%rip)
```

[perf]: https://perf.rust-lang.org/compare.html?start=a7e4de13c1785819f4d61da41f6704ed69d5f203&end=64fbb4f0b2d621ff46d559d1e9f5ad89a8d7789b&stat=instructions:u

compiler/rustc_codegen_cranelift/example/mini_core.rs

@@ -465,6 +465,36 @@ pub fn panic(_msg: &'static str) -> ! {
     }
 }
 
+macro_rules! panic_const {
+    ($($lang:ident = $message:expr,)+) => {
+        #[cfg(not(bootstrap))]
+        pub mod panic_const {
+            use super::*;
+
+            $(
+                #[track_caller]
+                #[lang = stringify!($lang)]
+                pub fn $lang() -> ! {
+                    panic($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",
+}
+
 #[lang = "panic_bounds_check"]
 #[track_caller]
 fn panic_bounds_check(index: usize, len: usize) -> ! {

compiler/rustc_codegen_cranelift/src/base.rs

@@ -372,8 +372,14 @@ fn codegen_fn_body(fx: &mut FunctionCx<'_, '_, '_>, start_block: Block) {
                         );
                     }
                     _ => {
-                        let msg_str = msg.description();
-                        codegen_panic(fx, msg_str, source_info);
+                        let location = fx.get_caller_location(source_info).load_scalar(fx);
+
+                        codegen_panic_inner(
+                            fx,
+                            msg.panic_function(),
+                            &[location],
+                            Some(source_info.span),
+                        );
                     }
                 }
             }
@@ -957,20 +963,6 @@ pub(crate) fn codegen_operand<'tcx>(
     }
 }
 
-pub(crate) fn codegen_panic<'tcx>(
-    fx: &mut FunctionCx<'_, '_, 'tcx>,
-    msg_str: &str,
-    source_info: mir::SourceInfo,
-) {
-    let location = fx.get_caller_location(source_info).load_scalar(fx);
-
-    let msg_ptr = fx.anonymous_str(msg_str);
-    let msg_len = fx.bcx.ins().iconst(fx.pointer_type, i64::try_from(msg_str.len()).unwrap());
-    let args = [msg_ptr, msg_len, location];
-
-    codegen_panic_inner(fx, rustc_hir::LangItem::Panic, &args, Some(source_info.span));
-}
-
 pub(crate) fn codegen_panic_nounwind<'tcx>(
     fx: &mut FunctionCx<'_, '_, 'tcx>,
     msg_str: &str,

compiler/rustc_codegen_gcc/example/mini_core.rs

@@ -418,6 +418,36 @@ pub fn panic(_msg: &'static str) -> ! {
     }
 }
 
+macro_rules! panic_const {
+    ($($lang:ident = $message:expr,)+) => {
+        #[cfg(not(bootstrap))]
+        pub mod panic_const {
+            use super::*;
+
+            $(
+                #[track_caller]
+                #[lang = stringify!($lang)]
+                pub fn $lang() -> ! {
+                    panic($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",
+}
+
 #[lang = "panic_cannot_unwind"]
 fn panic_cannot_unwind() -> ! {
     unsafe {

compiler/rustc_codegen_ssa/src/mir/block.rs

@@ -682,10 +682,8 @@ 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.panic_function(), vec![location])
             }
         };
 

compiler/rustc_hir/src/lang_items.rs

@@ -248,6 +248,25 @@ 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 panic_function(&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 { .. } => {
@@ -198,7 +199,7 @@ impl<O> AssertKind<O> {
     /// Format the message arguments for the `assert(cond, msg..)` terminator in MIR printing.
     ///
     /// Needs to be kept in sync with the run-time behavior (which is defined by
-    /// `AssertKind::description` and the lang items mentioned in its docs).
+    /// `AssertKind::panic_function` and the lang items mentioned in its docs).
     /// Note that we deliberately show more details here than we do at runtime, such as the actual
     /// numbers that overflowed -- it is much easier to do so here than at runtime.
     pub fn fmt_assert_args<W: fmt::Write>(&self, f: &mut W) -> fmt::Result
@@ -246,20 +247,44 @@ 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\"")
+            }
         }
     }
 
     /// Format the diagnostic message for use in a lint (e.g. when the assertion fails during const-eval).
     ///
     /// Needs to be kept in sync with the run-time behavior (which is defined by
-    /// `AssertKind::description` and the lang items mentioned in its docs).
+    /// `AssertKind::panic_function` and the lang items mentioned in its docs).
     /// Note that we deliberately show more details here than we do at runtime, such as the actual
     /// numbers that overflowed -- it is much easier to do so here than at runtime.
     pub fn diagnostic_message(&self) -> DiagMessage {

compiler/rustc_monomorphize/src/collector.rs

@@ -971,16 +971,17 @@ 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.panic_function());
+                }
+            },
             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,