Add funnel_sh{l,r} functions and intrinsics

 - Add a fallback implementation for the intrinsics
 - Add LLVM backend support for funnel shifts

Co-Authored-By: folkertdev <[email protected]>

Author: sayantn

tests/fail/intrinsics/funnel_shl.rs

@@ -0,0 +1,7 @@
+#![feature(core_intrinsics, funnel_shifts)]
+
+fn main() {
+    unsafe {
+        std::intrinsics::unchecked_funnel_shl(1_u32, 2, 32); //~ ERROR: Undefined Behavior
+    }
+}

tests/fail/intrinsics/funnel_shl.stderr

@@ -0,0 +1,15 @@
+error: Undefined Behavior: `assume` called with `false`
+  --> tests/fail/intrinsics/funnel_shl.rs:LL:CC
+   |
+LL |         std::intrinsics::unchecked_funnel_shl(1_u32, 2, 32);
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Undefined Behavior occurred here
+   |
+   = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
+   = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
+   = note: BACKTRACE:
+   = note: inside `main` at tests/fail/intrinsics/funnel_shl.rs:LL:CC
+
+note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
+
+error: aborting due to 1 previous error
+

tests/fail/intrinsics/funnel_shr.rs

@@ -0,0 +1,7 @@
+#![feature(core_intrinsics, funnel_shifts)]
+
+fn main() {
+    unsafe {
+        std::intrinsics::unchecked_funnel_shr(1_u32, 2, 32); //~ ERROR: Undefined Behavior
+    }
+}

tests/fail/intrinsics/funnel_shr.stderr

@@ -0,0 +1,15 @@
+error: Undefined Behavior: `assume` called with `false`
+  --> tests/fail/intrinsics/funnel_shr.rs:LL:CC
+   |
+LL |         std::intrinsics::unchecked_funnel_shr(1_u32, 2, 32);
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Undefined Behavior occurred here
+   |
+   = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
+   = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
+   = note: BACKTRACE:
+   = note: inside `main` at tests/fail/intrinsics/funnel_shr.rs:LL:CC
+
+note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
+
+error: aborting due to 1 previous error
+

tests/pass/intrinsics/integer.rs

@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: MIT OR Apache-2.0
 // SPDX-FileCopyrightText: The Rust Project Developers (see https://thanks.rust-lang.org)
 
-#![feature(core_intrinsics)]
+#![feature(core_intrinsics, funnel_shifts)]
 use std::intrinsics::*;
 
 pub fn main() {
@@ -143,5 +143,11 @@ pub fn main() {
 
         assert_eq!(unchecked_mul(6u8, 7), 42);
         assert_eq!(unchecked_mul(13, -5), -65);
+
+        assert_eq!(unchecked_funnel_shl(1_u32, 2, 5), 32);
+        assert_eq!(unchecked_funnel_shl(1_u32, 2, 31), 0x80000001);
+
+        assert_eq!(unchecked_funnel_shr(1_u32, 2, 5), 0x08000000);
+        assert_eq!(unchecked_funnel_shr(1_u32, 2, 31), 2);
     }
 }