From 915a04e2a401919d8b0e152331c839df471577b7 Mon Sep 17 00:00:00 2001
From: Simonas Kazlauskas <git@kazlauskas.me>
Date: Thu, 31 Dec 2020 18:02:52 +0200
Subject: [PATCH] Consider Scalar to be a bool only if its unsigned

This seems right, given that conceptually bools are unsigned, but the
implications of this change may have more action at distance that I'm
not sure how to exhaustively consider.

For instance there are a number of cases where code attaches range
metadata if `scalar.is_bool()` holds. Supposedly it would no longer be
attached to the `repr(i8)` enums? Though I'm not sure why booleans are
being special-cased here in the first place...

Fixes #80556
---
 compiler/rustc_target/src/abi/call/mod.rs |  7 ++++++-
 compiler/rustc_target/src/abi/mod.rs      |  2 +-
 src/test/codegen/abi-repr-ext.rs          | 13 +++++++++++++
 3 files changed, 20 insertions(+), 2 deletions(-)
 create mode 100644 src/test/codegen/abi-repr-ext.rs

diff --git a/compiler/rustc_target/src/abi/call/mod.rs b/compiler/rustc_target/src/abi/call/mod.rs
index aa1c31bda54..ce8e56b1949 100644
--- a/compiler/rustc_target/src/abi/call/mod.rs
+++ b/compiler/rustc_target/src/abi/call/mod.rs
@@ -103,7 +103,12 @@ impl ArgAttributes {
     }
 
     pub fn ext(&mut self, ext: ArgExtension) -> &mut Self {
-        assert!(self.arg_ext == ArgExtension::None || self.arg_ext == ext);
+        assert!(
+            self.arg_ext == ArgExtension::None || self.arg_ext == ext,
+            "cannot set {:?} when {:?} is already set",
+            ext,
+            self.arg_ext
+        );
         self.arg_ext = ext;
         self
     }
diff --git a/compiler/rustc_target/src/abi/mod.rs b/compiler/rustc_target/src/abi/mod.rs
index 88b2923f6c4..b14b1ef00db 100644
--- a/compiler/rustc_target/src/abi/mod.rs
+++ b/compiler/rustc_target/src/abi/mod.rs
@@ -682,7 +682,7 @@ pub struct Scalar {
 
 impl Scalar {
     pub fn is_bool(&self) -> bool {
-        if let Int(I8, _) = self.value { self.valid_range == (0..=1) } else { false }
+        matches!(self.value, Int(I8, false)) && self.valid_range == (0..=1)
     }
 
     /// Returns the valid range as a `x..y` range.
diff --git a/src/test/codegen/abi-repr-ext.rs b/src/test/codegen/abi-repr-ext.rs
new file mode 100644
index 00000000000..f93ccd79411
--- /dev/null
+++ b/src/test/codegen/abi-repr-ext.rs
@@ -0,0 +1,13 @@
+#![crate_type="lib"]
+
+#[repr(i8)]
+pub enum Type {
+    Type1 = 0,
+    Type2 = 1
+}
+
+// CHECK: define signext i8 @test()
+#[no_mangle]
+pub extern "C" fn test() -> Type {
+    Type::Type1
+}