Auto merge of #30085 - oli-obk:fix/pnkfelix_test, r=pnkfelix

for discussion see https://github.com/rust-lang/rust/pull/26848/files#r43151926

r? @pnkfelix

src/test/run-pass/shift-near-oflo.rs

@@ -18,39 +18,51 @@ fn main() {
     test_right_shift();
 }
 
+pub static mut HACK: i32 = 0;
+
+// Work around constant-evaluation
+// The point of this test is to exercise the code generated for execution at runtime,
+// `id` can never be flagged as a const fn by future aggressive analyses...
+// due to the modification of the static
+#[inline(never)]
+fn id<T>(x: T) -> T {
+    unsafe { HACK += 1; }
+    x
+}
+
 fn test_left_shift() {
     // negative rhs can panic, but values in [0,N-1] are okay for iN
 
     macro_rules! tests {
         ($iN:ty, $uN:ty, $max_rhs:expr, $expect_i:expr, $expect_u:expr) => { {
-            let x = (1 as $iN) << 0;
+            let x = (1 as $iN) << id(0);
             assert_eq!(x, 1);
-            let x = (1 as $uN) << 0;
+            let x = (1 as $uN) << id(0);
             assert_eq!(x, 1);
-            let x = (1 as $iN) << $max_rhs;
+            let x = (1 as $iN) << id($max_rhs);
             assert_eq!(x, $expect_i);
-            let x = (1 as $uN) << $max_rhs;
+            let x = (1 as $uN) << id($max_rhs);
             assert_eq!(x, $expect_u);
             // high-order bits on LHS are silently discarded without panic.
-            let x = (3 as $iN) << $max_rhs;
+            let x = (3 as $iN) << id($max_rhs);
             assert_eq!(x, $expect_i);
-            let x = (3 as $uN) << $max_rhs;
+            let x = (3 as $uN) << id($max_rhs);
             assert_eq!(x, $expect_u);
         } }
     }
 
-    let x = 1_i8 << 0;
+    let x = 1_i8 << id(0);
     assert_eq!(x, 1);
-    let x = 1_u8 << 0;
+    let x = 1_u8 << id(0);
     assert_eq!(x, 1);
-    let x = 1_i8 << 7;
+    let x = 1_i8 << id(7);
     assert_eq!(x, std::i8::MIN);
-    let x = 1_u8 << 7;
+    let x = 1_u8 << id(7);
     assert_eq!(x, 0x80);
     // high-order bits on LHS are silently discarded without panic.
-    let x = 3_i8 << 7;
+    let x = 3_i8 << id(7);
     assert_eq!(x, std::i8::MIN);
-    let x = 3_u8 << 7;
+    let x = 3_u8 << id(7);
     assert_eq!(x, 0x80);
 
     // above is (approximately) expanded from:
@@ -68,23 +80,23 @@ fn test_right_shift() {
         ($iN:ty, $uN:ty, $max_rhs:expr,
          $signbit_i:expr, $highbit_i:expr, $highbit_u:expr) =>
         { {
-            let x = (1 as $iN) >> 0;
+            let x = (1 as $iN) >> id(0);
             assert_eq!(x, 1);
-            let x = (1 as $uN) >> 0;
+            let x = (1 as $uN) >> id(0);
             assert_eq!(x, 1);
-            let x = ($highbit_i) >> $max_rhs-1;
+            let x = ($highbit_i) >> id($max_rhs-1);
             assert_eq!(x, 1);
-            let x = ($highbit_u) >> $max_rhs;
+            let x = ($highbit_u) >> id($max_rhs);
             assert_eq!(x, 1);
             // sign-bit is carried by arithmetic right shift
-            let x = ($signbit_i) >> $max_rhs;
+            let x = ($signbit_i) >> id($max_rhs);
             assert_eq!(x, -1);
             // low-order bits on LHS are silently discarded without panic.
-            let x = ($highbit_i + 1) >> $max_rhs-1;
+            let x = ($highbit_i + 1) >> id($max_rhs-1);
             assert_eq!(x, 1);
-            let x = ($highbit_u + 1) >> $max_rhs;
+            let x = ($highbit_u + 1) >> id($max_rhs);
             assert_eq!(x, 1);
-            let x = ($signbit_i + 1) >> $max_rhs;
+            let x = ($signbit_i + 1) >> id($max_rhs);
             assert_eq!(x, -1);
         } }
     }