Auto merge of #58985 - dlrobertson:fix_58980, r=alexreg

Fix segfaults in release build C-variadic fns

`va_start` and `va_end` must be called to initialize/cleanup the
"spoofed" `VaList` in a Rust defined C-variadic function even  if
the `VaList` is not used.

r? @alexreg
Fixes: #58980

2 files changed, 8 insertions, 9 deletions

diff --git a/src/librustc_codegen_ssa/mir/block.rs b/src/librustc_codegen_ssa/mir/block.rs
index 02086c7730c..35fd30f34ad 100644
--- a/src/librustc_codegen_ssa/mir/block.rs
+++ b/src/librustc_codegen_ssa/mir/block.rs
@@ -233,8 +233,13 @@ impl<'a, 'tcx: 'a, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         mut bx: Bx,
     ) {
         if self.fn_ty.c_variadic {
-            if let Some(va_list) = self.va_list_ref {
-                bx.va_end(va_list.llval);
+            match self.va_list_ref {
+                Some(va_list) => {
+                    bx.va_end(va_list.llval);
+                }
+                None => {
+                    bug!("C-variadic function must have a `va_list_ref`");
+                }
             }
         }
         let llval = match self.fn_ty.ret.mode {
diff --git a/src/librustc_codegen_ssa/mir/mod.rs b/src/librustc_codegen_ssa/mir/mod.rs
index 870b97401f4..c1b7502cd8f 100644
--- a/src/librustc_codegen_ssa/mir/mod.rs
+++ b/src/librustc_codegen_ssa/mir/mod.rs
@@ -532,13 +532,7 @@ fn arg_local_refs<'a, 'tcx: 'a, Bx: BuilderMethods<'a, 'tcx>>(
                 PassMode::Ignore(IgnoreMode::Zst) => {
                     return local(OperandRef::new_zst(bx.cx(), arg.layout));
                 }
-                PassMode::Ignore(IgnoreMode::CVarArgs) => {
-                    let backend_type = bx.cx().immediate_backend_type(arg.layout);
-                    return local(OperandRef {
-                        val: OperandValue::Immediate(bx.cx().const_undef(backend_type)),
-                        layout: arg.layout,
-                    });
-                }
+                PassMode::Ignore(IgnoreMode::CVarArgs) => {}
                 PassMode::Direct(_) => {
                     let llarg = bx.get_param(bx.llfn(), llarg_idx as c_uint);
                     bx.set_value_name(llarg, &name);