Auto merge of #136575 - scottmcm:nsuw-math, r=nikic

Set both `nuw` and `nsw` in slice size calculation

There's an old note in the code to do this, and now that [LLVM-C has an API for it](https://github.com/llvm/llvm-project/blob/f0b8ff12519270adcfef93410abff76ab073476a/llvm/include/llvm-c/Core.h#L4403-L4408), we might as well.  And it's been there since what looks like LLVM 17 https://github.com/llvm/llvm-project/commit/de9b6aa341d8951625d62ae3dac8670ebb3eb006 so doesn't even need to be conditional.

(There's other places, like `RawVecInner` or `Layout`, that might want to do things like this too, but I'll leave those for a future PR.)

2 files changed, 15 insertions, 5 deletions

diff --git a/tests/codegen/issues/issue-96497-slice-size-nowrap.rs b/tests/codegen/issues/issue-96497-slice-size-nowrap.rs
index dce156dd425..7b3a20a295e 100644
--- a/tests/codegen/issues/issue-96497-slice-size-nowrap.rs
+++ b/tests/codegen/issues/issue-96497-slice-size-nowrap.rs
@@ -11,7 +11,7 @@
 pub fn simple_size_of_nowrap(x: &[u32]) -> usize {
     // Make sure the shift used to compute the size has a nowrap flag.
 
-    // CHECK: [[A:%.*]] = shl nsw {{.*}}, 2
+    // CHECK: [[A:%.*]] = shl nuw nsw {{.*}}, 2
     // CHECK-NEXT: ret {{.*}} [[A]]
     core::mem::size_of_val(x)
 }
@@ -26,3 +26,13 @@ pub fn drop_write(mut x: Box<[u32]>) {
     // CHECK-NOT: store i32 42
     x[1] = 42;
 }
+
+// CHECK-LABEL: @slice_size_plus_2
+#[no_mangle]
+pub fn slice_size_plus_2(x: &[u16]) -> usize {
+    // Before #136575 this didn't get the `nuw` in the add.
+
+    // CHECK: [[BYTES:%.+]] = shl nuw nsw {{i16|i32|i64}} %x.1, 1
+    // CHECK: = add nuw {{i16|i32|i64}} [[BYTES]], 2
+    core::mem::size_of_val(x) + 2
+}
diff --git a/tests/codegen/slice-ref-equality.rs b/tests/codegen/slice-ref-equality.rs
index a5046a75944..2940378da3c 100644
--- a/tests/codegen/slice-ref-equality.rs
+++ b/tests/codegen/slice-ref-equality.rs
@@ -47,7 +47,7 @@ pub fn is_zero_array(data: &[u8; 4]) -> bool {
 #[no_mangle]
 fn eq_slice_of_nested_u8(x: &[[u8; 3]], y: &[[u8; 3]]) -> bool {
     // CHECK: icmp eq [[USIZE]] %x.1, %y.1
-    // CHECK: %[[BYTES:.+]] = mul nsw [[USIZE]] {{%x.1|%y.1}}, 3
+    // CHECK: %[[BYTES:.+]] = mul nuw nsw [[USIZE]] {{%x.1|%y.1}}, 3
     // CHECK: tail call{{( noundef)?}} i32 @{{bcmp|memcmp}}(ptr
     // CHECK-SAME: , [[USIZE]]{{( noundef)?}} %[[BYTES]])
     x == y
@@ -59,7 +59,7 @@ fn eq_slice_of_nested_u8(x: &[[u8; 3]], y: &[[u8; 3]]) -> bool {
 #[no_mangle]
 fn eq_slice_of_i32(x: &[i32], y: &[i32]) -> bool {
     // CHECK: icmp eq [[USIZE]] %x.1, %y.1
-    // CHECK: %[[BYTES:.+]] = shl nsw [[USIZE]] {{%x.1|%y.1}}, 2
+    // CHECK: %[[BYTES:.+]] = shl nuw nsw [[USIZE]] {{%x.1|%y.1}}, 2
     // CHECK: tail call{{( noundef)?}} i32 @{{bcmp|memcmp}}(ptr
     // CHECK-SAME: , [[USIZE]]{{( noundef)?}} %[[BYTES]])
     x == y
@@ -71,7 +71,7 @@ fn eq_slice_of_i32(x: &[i32], y: &[i32]) -> bool {
 #[no_mangle]
 fn eq_slice_of_nonzero(x: &[NonZero<i32>], y: &[NonZero<i32>]) -> bool {
     // CHECK: icmp eq [[USIZE]] %x.1, %y.1
-    // CHECK: %[[BYTES:.+]] = shl nsw [[USIZE]] {{%x.1|%y.1}}, 2
+    // CHECK: %[[BYTES:.+]] = shl nuw nsw [[USIZE]] {{%x.1|%y.1}}, 2
     // CHECK: tail call{{( noundef)?}} i32 @{{bcmp|memcmp}}(ptr
     // CHECK-SAME: , [[USIZE]]{{( noundef)?}} %[[BYTES]])
     x == y
@@ -83,7 +83,7 @@ fn eq_slice_of_nonzero(x: &[NonZero<i32>], y: &[NonZero<i32>]) -> bool {
 #[no_mangle]
 fn eq_slice_of_option_of_nonzero(x: &[Option<NonZero<i16>>], y: &[Option<NonZero<i16>>]) -> bool {
     // CHECK: icmp eq [[USIZE]] %x.1, %y.1
-    // CHECK: %[[BYTES:.+]] = shl nsw [[USIZE]] {{%x.1|%y.1}}, 1
+    // CHECK: %[[BYTES:.+]] = shl nuw nsw [[USIZE]] {{%x.1|%y.1}}, 1
     // CHECK: tail call{{( noundef)?}} i32 @{{bcmp|memcmp}}(ptr
     // CHECK-SAME: , [[USIZE]]{{( noundef)?}} %[[BYTES]])
     x == y