Change rustc_codegen_ssa's atomic_cmpxchg interface to return a pair of values

Author: Bernd Schmidt

compiler/rustc_codegen_gcc/src/builder.rs

@@ -1296,7 +1296,7 @@ impl<'a, 'gcc, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'gcc, 'tcx> {
     }
 
     // Atomic Operations
-    fn atomic_cmpxchg(&mut self, dst: RValue<'gcc>, cmp: RValue<'gcc>, src: RValue<'gcc>, order: AtomicOrdering, failure_order: AtomicOrdering, weak: bool) -> RValue<'gcc> {
+    fn atomic_cmpxchg(&mut self, dst: RValue<'gcc>, cmp: RValue<'gcc>, src: RValue<'gcc>, order: AtomicOrdering, failure_order: AtomicOrdering, weak: bool) -> (RValue<'gcc>, RValue<'gcc>) {
         let expected = self.current_func().new_local(None, cmp.get_type(), "expected");
         self.llbb().add_assignment(None, expected, cmp);
         // NOTE: gcc doesn't support a failure memory model that is stronger than the success
@@ -1310,20 +1310,12 @@ impl<'a, 'gcc, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'gcc, 'tcx> {
             };
         let success = self.compare_exchange(dst, expected, src, order, failure_order, weak);
 
-        let pair_type = self.cx.type_struct(&[src.get_type(), self.bool_type], false);
-        let result = self.current_func().new_local(None, pair_type, "atomic_cmpxchg_result");
-        let align = Align::from_bits(64).expect("align"); // TODO(antoyo): use good align.
+        // NOTE: since success contains the call to the intrinsic, it must be added to the basic block before
+        // expected so that we store expected after the call.
+        let success_var = self.current_func().new_local(None, self.bool_type, "success");
+        self.llbb().add_assignment(None, success_var, success);
 
-        let value_type = result.to_rvalue().get_type();
-        if let Some(struct_type) = value_type.is_struct() {
-            self.store(success, result.access_field(None, struct_type.get_field(1)).get_address(None), align);
-            // NOTE: since success contains the call to the intrinsic, it must be stored before
-            // expected so that we store expected after the call.
-            self.store(expected.to_rvalue(), result.access_field(None, struct_type.get_field(0)).get_address(None), align);
-        }
-        // TODO(antoyo): handle when value is not a struct.
-
-        result.to_rvalue()
+        (expected.to_rvalue(), success_var.to_rvalue())
     }
 
     fn atomic_rmw(&mut self, op: AtomicRmwBinOp, dst: RValue<'gcc>, src: RValue<'gcc>, order: AtomicOrdering) -> RValue<'gcc> {

compiler/rustc_codegen_llvm/src/builder.rs

@@ -1080,7 +1080,7 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
         order: rustc_codegen_ssa::common::AtomicOrdering,
         failure_order: rustc_codegen_ssa::common::AtomicOrdering,
         weak: bool,
-    ) -> &'ll Value {
+    ) -> (&'ll Value, &'ll Value) {
         let weak = if weak { llvm::True } else { llvm::False };
         unsafe {
             let value = llvm::LLVMBuildAtomicCmpXchg(
@@ -1093,7 +1093,9 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
                 llvm::False, // SingleThreaded
             );
             llvm::LLVMSetWeak(value, weak);
-            value
+            let val = self.extract_value(value, 0);
+            let success = self.extract_value(value, 1);
+            (val, success)
         }
     }
     fn atomic_rmw(

compiler/rustc_codegen_ssa/src/mir/intrinsic.rs

@@ -339,16 +339,14 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                                 cmp = bx.ptrtoint(cmp, bx.type_isize());
                                 src = bx.ptrtoint(src, bx.type_isize());
                             }
-                            let pair = bx.atomic_cmpxchg(
+                            let (val, success) = bx.atomic_cmpxchg(
                                 dst,
                                 cmp,
                                 src,
                                 parse_ordering(bx, success),
                                 parse_ordering(bx, failure),
                                 weak,
                             );
-                            let val = bx.extract_value(pair, 0);
-                            let success = bx.extract_value(pair, 1);
                             let val = bx.from_immediate(val);
                             let success = bx.from_immediate(success);
 

compiler/rustc_codegen_ssa/src/traits/builder.rs

@@ -296,7 +296,7 @@ pub trait BuilderMethods<'a, 'tcx>:
         order: AtomicOrdering,
         failure_order: AtomicOrdering,
         weak: bool,
-    ) -> Self::Value;
+    ) -> (Self::Value, Self::Value);
     fn atomic_rmw(
         &mut self,
         op: AtomicRmwBinOp,