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

1 files changed, 19 insertions, 0 deletions

diff --git a/src/test/codegen/c-variadic-opt.rs b/src/test/codegen/c-variadic-opt.rs
new file mode 100644
index 00000000000..8594d309b0a
--- /dev/null
+++ b/src/test/codegen/c-variadic-opt.rs
@@ -0,0 +1,19 @@
+// compile-flags: -C opt-level=3
+
+#![crate_type = "lib"]
+#![feature(c_variadic)]
+#![no_std]
+use core::ffi::VaList;
+
+extern "C" {
+    fn vprintf(fmt: *const i8, ap: VaList) -> i32;
+}
+
+// Ensure that `va_start` and `va_end` are properly injected even
+// when the "spoofed" `VaList` is not used.
+#[no_mangle]
+pub unsafe extern "C" fn c_variadic_no_use(fmt: *const i8, mut ap: ...) -> i32 {
+    // CHECK: call void @llvm.va_start
+    vprintf(fmt, ap)
+    // CHECK: call void @llvm.va_end
+}