Auto merge of rust-lang#78253 - Aaron1011:bump-llvm-deadarg, r=cuviper

Bump LLVM for DeadArgElim fix

Fixes rust-lang#76387

Pulls in rust-lang/llvm-project#82

Author: bors

src/llvm-project

@@ -0,0 +1,29 @@
+// compile-flags: -C opt-level=3
+
+pub struct FatPtr {
+    ptr: *mut u8,
+    len: usize,
+}
+
+impl FatPtr {
+    pub fn new(len: usize) -> FatPtr {
+        let ptr = Box::into_raw(vec![42u8; len].into_boxed_slice()) as *mut u8;
+
+        FatPtr { ptr, len }
+    }
+}
+
+impl std::ops::Deref for FatPtr {
+    type Target = [u8];
+
+    #[inline]
+    fn deref(&self) -> &[u8] {
+        unsafe { std::slice::from_raw_parts(self.ptr, self.len) }
+    }
+}
+
+impl std::ops::Drop for FatPtr {
+    fn drop(&mut self) {
+        println!("Drop");
+    }
+}

src/test/ui/auxiliary/issue-76387.rs

@@ -0,0 +1,22 @@
+// no-system-llvm
+// compile-flags: -C opt-level=3
+// aux-build: issue-76387.rs
+// run-pass
+
+// Regression test for issue #76387
+// Tests that LLVM doesn't miscompile this
+
+extern crate issue_76387;
+
+use issue_76387::FatPtr;
+
+fn print(data: &[u8]) {
+    println!("{:#?}", data);
+}
+
+fn main() {
+    let ptr = FatPtr::new(20);
+    let data = unsafe { std::slice::from_raw_parts(ptr.as_ptr(), ptr.len()) };
+
+    print(data);
+}