Rollup merge of #78252 - bugadani:issue-45964, r=Mark-Simulacrum

Add codegen test for #45964

Closes #45964

src/test/codegen/issue-45964-bounds-check-slice-pos.rs

@@ -0,0 +1,38 @@
+// This test case checks that slice::{r}position functions do not
+// prevent optimizing away bounds checks
+
+// compile-flags: -O
+
+#![crate_type="rlib"]
+
+// CHECK-LABEL: @test
+#[no_mangle]
+pub fn test(y: &[u32], x: &u32, z: &u32) -> bool {
+    let result = match y.iter().position(|a| a == x) {
+        Some(p) => Ok(p),
+        None => Err(()),
+    };
+
+    if let Ok(p) = result {
+        // CHECK-NOT: panic
+        y[p] == *z
+    } else {
+        false
+    }
+}
+
+// CHECK-LABEL: @rtest
+#[no_mangle]
+pub fn rtest(y: &[u32], x: &u32, z: &u32) -> bool {
+    let result = match y.iter().rposition(|a| a == x) {
+        Some(p) => Ok(p),
+        None => Err(()),
+    };
+
+    if let Ok(p) = result {
+        // CHECK-NOT: panic
+        y[p] == *z
+    } else {
+        false
+    }
+}