Lazy anon const default substs

compiler/rustc_codegen_llvm/src/builder.rs

@@ -928,8 +928,12 @@ impl BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
         pers_fn: &'ll Value,
         num_clauses: usize,
     ) -> &'ll Value {
+        // Use LLVMSetPersonalityFn to set the personality. It supports arbitrary Consts while,
+        // LLVMBuildLandingPad requires the argument to be a Function (as of LLVM 12). The
+        // personality lives on the parent function anyway.
+        self.set_personality_fn(pers_fn);
         unsafe {
-            llvm::LLVMBuildLandingPad(self.llbuilder, ty, pers_fn, num_clauses as c_uint, UNNAMED)
+            llvm::LLVMBuildLandingPad(self.llbuilder, ty, None, num_clauses as c_uint, UNNAMED)
         }
     }
 

compiler/rustc_codegen_llvm/src/context.rs

@@ -386,11 +386,16 @@ impl MiscMethods<'tcx> for CodegenCx<'ll, 'tcx> {
                 } else {
                     "rust_eh_personality"
                 };
-                let fty = self.type_variadic_func(&[], self.type_i32());
-                self.declare_cfn(name, llvm::UnnamedAddr::Global, fty)
+                if let Some(llfn) = self.get_declared_value(name) {
+                    llfn
+                } else {
+                    let fty = self.type_variadic_func(&[], self.type_i32());
+                    let llfn = self.declare_cfn(name, llvm::UnnamedAddr::Global, fty);
+                    attributes::apply_target_cpu_attr(self, llfn);
+                    llfn
+                }
             }
         };
-        attributes::apply_target_cpu_attr(self, llfn);
         self.eh_personality.set(Some(llfn));
         llfn
     }

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -1165,7 +1165,7 @@ extern "C" {
     pub fn LLVMBuildLandingPad(
         B: &Builder<'a>,
         Ty: &'a Type,
-        PersFn: &'a Value,
+        PersFn: Option<&'a Value>,
         NumClauses: c_uint,
         Name: *const c_char,
     ) -> &'a Value;

src/test/ui/panic-runtime/incompatible-type.rs

@@ -0,0 +1,24 @@
+// Check that rust_eh_personality can have a different type signature than the
+// one hardcoded in the compiler.  Regression test for #70117. Used to fail with:
+//
+// Assertion `isa<X>(Val) && "cast<Ty>() argument of incompatible type!"' failed.
+//
+// build-pass
+// compile-flags: --crate-type=lib -Ccodegen-units=1
+#![no_std]
+#![panic_runtime]
+#![feature(panic_runtime)]
+#![feature(rustc_attrs)]
+
+pub struct DropMe;
+
+impl Drop for DropMe {
+    fn drop(&mut self) {}
+}
+
+pub fn test(_: DropMe) {
+    unreachable!();
+}
+
+#[rustc_std_internal_symbol]
+pub unsafe extern "C" fn rust_eh_personality() {}