Auto merge of #136735 - scottmcm:transmute-nonnull, r=oli-obk

`transmute` should also assume non-null pointers

Previously it only did integer-ABI things, but this way it does data pointers too.  That gives more information in general to the backend, and allows slightly simplifying one of the helpers in slice iterators.

3 files changed, 69 insertions, 4 deletions

diff --git a/tests/codegen/intrinsics/transmute-niched.rs b/tests/codegen/intrinsics/transmute-niched.rs
index 88119ccb8b2..5ded0e192fa 100644
--- a/tests/codegen/intrinsics/transmute-niched.rs
+++ b/tests/codegen/intrinsics/transmute-niched.rs
@@ -6,6 +6,7 @@
 
 use std::mem::transmute;
 use std::num::NonZero;
+use std::ptr::NonNull;
 
 #[repr(u8)]
 pub enum SmallEnum {
@@ -192,3 +193,31 @@ pub unsafe fn check_bool_to_ordering(x: bool) -> std::cmp::Ordering {
 
     transmute(x)
 }
+
+// CHECK-LABEL: @check_nonnull_to_ptr(
+#[no_mangle]
+pub unsafe fn check_nonnull_to_ptr(x: NonNull<u8>) -> *const u8 {
+    // CHECK-NOT: icmp
+    // CHECK-NOT: assume
+    // OPT: %0 = icmp ne ptr %x, null
+    // OPT: call void @llvm.assume(i1 %0)
+    // CHECK-NOT: icmp
+    // CHECK-NOT: assume
+    // CHECK: ret ptr %x
+
+    transmute(x)
+}
+
+// CHECK-LABEL: @check_ptr_to_nonnull(
+#[no_mangle]
+pub unsafe fn check_ptr_to_nonnull(x: *const u8) -> NonNull<u8> {
+    // CHECK-NOT: icmp
+    // CHECK-NOT: assume
+    // OPT: %0 = icmp ne ptr %x, null
+    // OPT: call void @llvm.assume(i1 %0)
+    // CHECK-NOT: icmp
+    // CHECK-NOT: assume
+    // CHECK: ret ptr %x
+
+    transmute(x)
+}
diff --git a/tests/codegen/intrinsics/transmute.rs b/tests/codegen/intrinsics/transmute.rs
index 541333a52b0..5b40a6a12c0 100644
--- a/tests/codegen/intrinsics/transmute.rs
+++ b/tests/codegen/intrinsics/transmute.rs
@@ -370,9 +370,11 @@ pub unsafe fn check_issue_110005(x: (usize, bool)) -> Option<Box<[u8]>> {
 #[no_mangle]
 pub unsafe fn check_pair_to_dst_ref<'a>(x: (usize, usize)) -> &'a [u8] {
     // CHECK: %_0.0 = getelementptr i8, ptr null, i64 %x.0
-    // CHECK: %0 = insertvalue { ptr, i64 } poison, ptr %_0.0, 0
-    // CHECK: %1 = insertvalue { ptr, i64 } %0, i64 %x.1, 1
-    // CHECK: ret { ptr, i64 } %1
+    // CHECK: %0 = icmp ne ptr %_0.0, null
+    // CHECK: call void @llvm.assume(i1 %0)
+    // CHECK: %1 = insertvalue { ptr, i64 } poison, ptr %_0.0, 0
+    // CHECK: %2 = insertvalue { ptr, i64 } %1, i64 %x.1, 1
+    // CHECK: ret { ptr, i64 } %2
     transmute(x)
 }
 
diff --git a/tests/codegen/slice-iter-len-eq-zero.rs b/tests/codegen/slice-iter-len-eq-zero.rs
index c85861d47f8..6998d98e498 100644
--- a/tests/codegen/slice-iter-len-eq-zero.rs
+++ b/tests/codegen/slice-iter-len-eq-zero.rs
@@ -1,4 +1,5 @@
 //@ compile-flags: -Copt-level=3
+//@ needs-deterministic-layouts (opposite scalar pair orders breaks it)
 #![crate_type = "lib"]
 
 type Demo = [u8; 3];
@@ -7,7 +8,40 @@ type Demo = [u8; 3];
 #[no_mangle]
 pub fn slice_iter_len_eq_zero(y: std::slice::Iter<'_, Demo>) -> bool {
     // CHECK-NOT: sub
-    // CHECK: %[[RET:.+]] = icmp eq ptr {{%1|%0}}, {{%1|%0}}
+    // CHECK: %[[RET:.+]] = icmp eq ptr {{%y.0, %y.1|%y.1, %y.0}}
+    // CHECK: ret i1 %[[RET]]
+    y.len() == 0
+}
+
+// CHECK-LABEL: @slice_iter_len_eq_zero_ref
+#[no_mangle]
+pub fn slice_iter_len_eq_zero_ref(y: &mut std::slice::Iter<'_, Demo>) -> bool {
+    // CHECK-NOT: sub
+    // CHECK: %[[A:.+]] = load ptr
+    // CHECK-SAME: !nonnull
+    // CHECK: %[[B:.+]] = load ptr
+    // CHECK-SAME: !nonnull
+    // CHECK: %[[RET:.+]] = icmp eq ptr %[[A]], %[[B]]
+    // CHECK: ret i1 %[[RET]]
+    y.len() == 0
+}
+
+struct MyZST;
+
+// CHECK-LABEL: @slice_zst_iter_len_eq_zero
+#[no_mangle]
+pub fn slice_zst_iter_len_eq_zero(y: std::slice::Iter<'_, MyZST>) -> bool {
+    // CHECK: %[[RET:.+]] = icmp eq ptr %y.1, null
+    // CHECK: ret i1 %[[RET]]
+    y.len() == 0
+}
+
+// CHECK-LABEL: @slice_zst_iter_len_eq_zero_ref
+#[no_mangle]
+pub fn slice_zst_iter_len_eq_zero_ref(y: &mut std::slice::Iter<'_, MyZST>) -> bool {
+    // CHECK: %[[LEN:.+]] = load ptr
+    // CHECK-NOT: !nonnull
+    // CHECK: %[[RET:.+]] = icmp eq ptr %[[LEN]], null
     // CHECK: ret i1 %[[RET]]
     y.len() == 0
 }