Rollup merge of #83916 - Amanieu:asm_anonconst, r=petrochenkov

Use AnonConst for asm! constants

This replaces the old system which used explicit promotion. See #83169 for more background.

The syntax for `const` operands is still the same as before: `const <expr>`.

Fixes #83169

Because the implementation is heavily based on inline consts, we suffer from the same issues:
- We lose the ability to use expressions derived from generics. See the deleted tests in `src/test/ui/asm/const.rs`.
- We are hitting the same ICEs as inline consts, for example #78174. It is unlikely that we will be able to stabilize this before inline consts are stabilized.

compiler/rustc_passes/src/intrinsicck.rs

@@ -347,7 +347,7 @@ impl ExprVisitor<'tcx> {
     }
 
     fn check_asm(&self, asm: &hir::InlineAsm<'tcx>) {
-        for (idx, (op, _op_sp)) in asm.operands.iter().enumerate() {
+        for (idx, (op, op_sp)) in asm.operands.iter().enumerate() {
             match *op {
                 hir::InlineAsmOperand::In { reg, ref expr } => {
                     self.check_asm_operand_type(idx, reg, expr, asm.template, None);
@@ -372,14 +372,15 @@ impl ExprVisitor<'tcx> {
                         );
                     }
                 }
-                hir::InlineAsmOperand::Const { ref expr } => {
-                    let ty = self.typeck_results.expr_ty_adjusted(expr);
-                    match ty.kind() {
+                hir::InlineAsmOperand::Const { ref anon_const } => {
+                    let anon_const_def_id = self.tcx.hir().local_def_id(anon_const.hir_id);
+                    let value = ty::Const::from_anon_const(self.tcx, anon_const_def_id);
+                    match value.ty.kind() {
                         ty::Int(_) | ty::Uint(_) | ty::Float(_) => {}
                         _ => {
                             let msg =
                                 "asm `const` arguments must be integer or floating-point values";
-                            self.tcx.sess.span_err(expr.span, msg);
+                            self.tcx.sess.span_err(*op_sp, msg);
                         }
                     }
                 }

compiler/rustc_passes/src/liveness.rs

@@ -1067,7 +1067,6 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
                 for (op, _op_sp) in asm.operands.iter().rev() {
                     match op {
                         hir::InlineAsmOperand::In { expr, .. }
-                        | hir::InlineAsmOperand::Const { expr, .. }
                         | hir::InlineAsmOperand::Sym { expr, .. } => {
                             succ = self.propagate_through_expr(expr, succ)
                         }
@@ -1085,6 +1084,7 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
                             }
                             succ = self.propagate_through_expr(in_expr, succ);
                         }
+                        hir::InlineAsmOperand::Const { .. } => {}
                     }
                 }
                 succ