From 03e5b5d539a79e69dac826590250f90fea99925a Mon Sep 17 00:00:00 2001
From: Ben Kimock <kimockb@gmail.com>
Date: Sun, 18 Feb 2024 19:42:27 -0500
Subject: [PATCH] Lower transmutes from int to pointer type as gep on null

---
 compiler/rustc_codegen_ssa/src/mir/rvalue.rs    | 4 ++--
 tests/codegen/intrinsics/transmute.rs           | 2 +-
 tests/codegen/transmute-scalar.rs               | 2 +-
 tests/ui/abi/foreign/foreign-call-no-runtime.rs | 6 +++---
 4 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
index 5c6060a7159aa..7b968b2806812 100644
--- a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
@@ -305,11 +305,11 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         imm = match (from_scalar.primitive(), to_scalar.primitive()) {
             (Int(..) | F32 | F64, Int(..) | F32 | F64) => bx.bitcast(imm, to_backend_ty),
             (Pointer(..), Pointer(..)) => bx.pointercast(imm, to_backend_ty),
-            (Int(..), Pointer(..)) => bx.inttoptr(imm, to_backend_ty),
+            (Int(..), Pointer(..)) => bx.gep(bx.type_i8(), bx.const_null(bx.type_ptr()), &[imm]),
             (Pointer(..), Int(..)) => bx.ptrtoint(imm, to_backend_ty),
             (F32 | F64, Pointer(..)) => {
                 let int_imm = bx.bitcast(imm, bx.cx().type_isize());
-                bx.inttoptr(int_imm, to_backend_ty)
+                bx.gep(bx.type_i8(), bx.const_null(bx.type_ptr()), &[int_imm])
             }
             (Pointer(..), F32 | F64) => {
                 let int_imm = bx.ptrtoint(imm, bx.cx().type_isize());
diff --git a/tests/codegen/intrinsics/transmute.rs b/tests/codegen/intrinsics/transmute.rs
index eff16050875c5..edc2f758bc0b0 100644
--- a/tests/codegen/intrinsics/transmute.rs
+++ b/tests/codegen/intrinsics/transmute.rs
@@ -371,7 +371,7 @@ pub unsafe fn check_issue_110005(x: (usize, bool)) -> Option<Box<[u8]>> {
 // CHECK-LABEL: @check_pair_to_dst_ref(
 #[no_mangle]
 pub unsafe fn check_pair_to_dst_ref<'a>(x: (usize, usize)) -> &'a [u8] {
-    // CHECK: %_0.0 = inttoptr i64 %x.0 to ptr
+    // 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
diff --git a/tests/codegen/transmute-scalar.rs b/tests/codegen/transmute-scalar.rs
index 39126b024a6e9..e7518f426da97 100644
--- a/tests/codegen/transmute-scalar.rs
+++ b/tests/codegen/transmute-scalar.rs
@@ -49,7 +49,7 @@ pub fn ptr_to_int(p: *mut u16) -> usize {
 }
 
 // CHECK: define{{.*}}ptr @int_to_ptr([[USIZE]] %i)
-// CHECK: %_0 = inttoptr [[USIZE]] %i to ptr
+// CHECK: %_0 = getelementptr i8, ptr null, i64 %i
 // CHECK-NEXT: ret ptr %_0
 #[no_mangle]
 pub fn int_to_ptr(i: usize) -> *mut u16 {
diff --git a/tests/ui/abi/foreign/foreign-call-no-runtime.rs b/tests/ui/abi/foreign/foreign-call-no-runtime.rs
index 7f847d55721c3..054d9d5cc85ce 100644
--- a/tests/ui/abi/foreign/foreign-call-no-runtime.rs
+++ b/tests/ui/abi/foreign/foreign-call-no-runtime.rs
@@ -40,21 +40,21 @@ pub fn main() {
 
 extern "C" fn callback_isize(data: libc::uintptr_t) {
     unsafe {
-        let data: *const isize = mem::transmute(data);
+        let data = data as *const isize;
         assert_eq!(*data, 100);
     }
 }
 
 extern "C" fn callback_i64(data: libc::uintptr_t) {
     unsafe {
-        let data: *const i64 = mem::transmute(data);
+        let data = data as *const i64;
         assert_eq!(*data, 100);
     }
 }
 
 extern "C" fn callback_i32(data: libc::uintptr_t) {
     unsafe {
-        let data: *const i32 = mem::transmute(data);
+        let data = data as *const i32;
         assert_eq!(*data, 100);
     }
 }