From 0f1d25e5564b6f497417e00ed417234a0df7a227 Mon Sep 17 00:00:00 2001
From: Erik Desjardins <erikdesjardins@users.noreply.github.com>
Date: Mon, 24 Aug 2020 13:15:20 -0400
Subject: [PATCH] Test that bounds checks are elided for indexing after
 .[r]position()

---
 ...issue-73396-bounds-check-after-position.rs | 78 +++++++++++++++++++
 1 file changed, 78 insertions(+)
 create mode 100644 src/test/codegen/issue-73396-bounds-check-after-position.rs

diff --git a/src/test/codegen/issue-73396-bounds-check-after-position.rs b/src/test/codegen/issue-73396-bounds-check-after-position.rs
new file mode 100644
index 00000000000..e5f3ae45c07
--- /dev/null
+++ b/src/test/codegen/issue-73396-bounds-check-after-position.rs
@@ -0,0 +1,78 @@
+// min-llvm-version: 11.0.0
+// compile-flags: -O
+// ignore-debug: the debug assertions get in the way
+#![crate_type = "lib"]
+
+// Make sure no bounds checks are emitted when slicing or indexing
+// with an index from `position()` or `rposition()`.
+
+// CHECK-LABEL: @position_slice_to_no_bounds_check
+#[no_mangle]
+pub fn position_slice_to_no_bounds_check(s: &[u8]) -> &[u8] {
+    // CHECK-NOT: panic
+    // CHECK-NOT: slice_index_len_fail
+    if let Some(idx) = s.iter().position(|b| *b == b'\\') {
+        &s[..idx]
+    } else {
+        s
+    }
+}
+
+// CHECK-LABEL: @position_slice_from_no_bounds_check
+#[no_mangle]
+pub fn position_slice_from_no_bounds_check(s: &[u8]) -> &[u8] {
+    // CHECK-NOT: panic
+    // CHECK-NOT: slice_index_len_fail
+    if let Some(idx) = s.iter().position(|b| *b == b'\\') {
+        &s[idx..]
+    } else {
+        s
+    }
+}
+
+// CHECK-LABEL: @position_index_no_bounds_check
+#[no_mangle]
+pub fn position_index_no_bounds_check(s: &[u8]) -> u8 {
+    // CHECK-NOT: panic
+    // CHECK-NOT: slice_index_len_fail
+    if let Some(idx) = s.iter().position(|b| *b == b'\\') {
+        s[idx]
+    } else {
+        42
+    }
+}
+// CHECK-LABEL: @rposition_slice_to_no_bounds_check
+#[no_mangle]
+pub fn rposition_slice_to_no_bounds_check(s: &[u8]) -> &[u8] {
+    // CHECK-NOT: panic
+    // CHECK-NOT: slice_index_len_fail
+    if let Some(idx) = s.iter().rposition(|b| *b == b'\\') {
+        &s[..idx]
+    } else {
+        s
+    }
+}
+
+// CHECK-LABEL: @rposition_slice_from_no_bounds_check
+#[no_mangle]
+pub fn rposition_slice_from_no_bounds_check(s: &[u8]) -> &[u8] {
+    // CHECK-NOT: panic
+    // CHECK-NOT: slice_index_len_fail
+    if let Some(idx) = s.iter().rposition(|b| *b == b'\\') {
+        &s[idx..]
+    } else {
+        s
+    }
+}
+
+// CHECK-LABEL: @rposition_index_no_bounds_check
+#[no_mangle]
+pub fn rposition_index_no_bounds_check(s: &[u8]) -> u8 {
+    // CHECK-NOT: panic
+    // CHECK-NOT: slice_index_len_fail
+    if let Some(idx) = s.iter().rposition(|b| *b == b'\\') {
+        s[idx]
+    } else {
+        42
+    }
+}