From 0c115bf8b8a6973711cb4e8b3c0f62e2551c20a5 Mon Sep 17 00:00:00 2001
From: Nikita Popov <npopov@redhat.com>
Date: Thu, 16 Mar 2023 14:56:02 +0100
Subject: [PATCH] Use poison instead of undef

In cases where it is legal, we should prefer poison values over
undef values.

This replaces undef with poison for aggregate construction and
for uninhabited types. There are more places where we can likely
use poison, but I wanted to stay conservative to start with.

In particular the aggregate case is important for newer LLVM
versions, which are not able to handle an undef base value during
early optimization due to poison-propagation concerns.
---
 src/common.rs | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/common.rs b/src/common.rs
index 76fc7bd222e1..ac04b61a3067 100644
--- a/src/common.rs
+++ b/src/common.rs
@@ -73,6 +73,11 @@ impl<'gcc, 'tcx> ConstMethods<'tcx> for CodegenCx<'gcc, 'tcx> {
         }
     }
 
+    fn const_poison(&self, typ: Type<'gcc>) -> RValue<'gcc> {
+        // No distinction between undef and poison.
+        self.const_undef(typ)
+    }
+
     fn const_int(&self, typ: Type<'gcc>, int: i64) -> RValue<'gcc> {
         self.gcc_int(typ, int)
     }