Auto merge of rust-lang#121282 - saethlin:gep-null-means-no-provenance, r=<try>

Lower transmutes from int to pointer type as gep on null

I thought of this while looking at rust-lang#121242

The UI test that's being changed here crashes without changing the transmutes into casts. Based on that, this PR should not be merged without a crater build-and-test run.

Author: bors

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());

tests/codegen/intrinsics/transmute.rs

@@ -296,7 +296,7 @@ pub unsafe fn check_pair_with_bool(x: (u8, bool)) -> (bool, i8) {
 pub unsafe fn check_float_to_pointer(x: f64) -> *const () {
     // CHECK-NOT: alloca
     // CHECK: %0 = bitcast double %x to i64
-    // CHECK: %_0 = inttoptr i64 %0 to ptr
+    // CHECK: %_0 = getelementptr i8, ptr null, i64 %0
     // CHECK: ret ptr %_0
     transmute(x)
 }
@@ -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

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 {

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);
     }
 }