Rollup merge of #103456 - scottmcm:fix-unchecked-shifts, r=scottmcm

`unchecked_{shl|shr}` should use `u32` as the RHS

The other shift methods, such as https://doc.rust-lang.org/nightly/std/primitive.u64.html#method.checked_shr and https://doc.rust-lang.org/nightly/std/primitive.i16.html#method.wrapping_shl, use `u32` for the shift amount.  That's consistent with other things, like `count_ones`, which also always use `u32` for a bit count, regardless of the size of the type.

This PR changes `unchecked_shl` and `unchecked_shr` to also use `u32` for the shift amount (rather than Self).

cc #85122, the `unchecked_math` tracking issue

1 files changed, 66 insertions, 0 deletions

diff --git a/src/test/codegen/unchecked_shifts.rs b/src/test/codegen/unchecked_shifts.rs
new file mode 100644
index 00000000000..60d0cb09aca
--- /dev/null
+++ b/src/test/codegen/unchecked_shifts.rs
@@ -0,0 +1,66 @@
+// compile-flags: -O
+// min-llvm-version: 15.0 (LLVM 13 in CI does this differently from submodule LLVM)
+// ignore-debug (because unchecked is checked in debug)
+
+#![crate_type = "lib"]
+#![feature(unchecked_math)]
+
+// CHECK-LABEL: @unchecked_shl_unsigned_same
+#[no_mangle]
+pub unsafe fn unchecked_shl_unsigned_same(a: u32, b: u32) -> u32 {
+    // CHECK-NOT: and i32
+    // CHECK: shl i32 %a, %b
+    // CHECK-NOT: and i32
+    a.unchecked_shl(b)
+}
+
+// CHECK-LABEL: @unchecked_shl_unsigned_smaller
+#[no_mangle]
+pub unsafe fn unchecked_shl_unsigned_smaller(a: u16, b: u32) -> u16 {
+    // This uses -DAG to avoid failing on irrelevant reorderings,
+    // like emitting the truncation earlier.
+
+    // CHECK-DAG: %[[INRANGE:.+]] = icmp ult i32 %b, 65536
+    // CHECK-DAG: tail call void @llvm.assume(i1 %[[INRANGE]])
+    // CHECK-DAG: %[[TRUNC:.+]] = trunc i32 %b to i16
+    // CHECK-DAG: shl i16 %a, %[[TRUNC]]
+    a.unchecked_shl(b)
+}
+
+// CHECK-LABEL: @unchecked_shl_unsigned_bigger
+#[no_mangle]
+pub unsafe fn unchecked_shl_unsigned_bigger(a: u64, b: u32) -> u64 {
+    // CHECK: %[[EXT:.+]] = zext i32 %b to i64
+    // CHECK: shl i64 %a, %[[EXT]]
+    a.unchecked_shl(b)
+}
+
+// CHECK-LABEL: @unchecked_shr_signed_same
+#[no_mangle]
+pub unsafe fn unchecked_shr_signed_same(a: i32, b: u32) -> i32 {
+    // CHECK-NOT: and i32
+    // CHECK: ashr i32 %a, %b
+    // CHECK-NOT: and i32
+    a.unchecked_shr(b)
+}
+
+// CHECK-LABEL: @unchecked_shr_signed_smaller
+#[no_mangle]
+pub unsafe fn unchecked_shr_signed_smaller(a: i16, b: u32) -> i16 {
+    // This uses -DAG to avoid failing on irrelevant reorderings,
+    // like emitting the truncation earlier.
+
+    // CHECK-DAG: %[[INRANGE:.+]] = icmp ult i32 %b, 32768
+    // CHECK-DAG: tail call void @llvm.assume(i1 %[[INRANGE]])
+    // CHECK-DAG: %[[TRUNC:.+]] = trunc i32 %b to i16
+    // CHECK-DAG: ashr i16 %a, %[[TRUNC]]
+    a.unchecked_shr(b)
+}
+
+// CHECK-LABEL: @unchecked_shr_signed_bigger
+#[no_mangle]
+pub unsafe fn unchecked_shr_signed_bigger(a: i64, b: u32) -> i64 {
+    // CHECK: %[[EXT:.+]] = zext i32 %b to i64
+    // CHECK: ashr i64 %a, %[[EXT]]
+    a.unchecked_shr(b)
+}