Rollup merge of #136543 - RalfJung:round-ties-even, r=tgross35

intrinsics: unify rint, roundeven, nearbyint in a single round_ties_even intrinsic

LLVM has three intrinsics here that all do the same thing (when used in the default FP environment). There's no reason Rust needs to copy that historically-grown mess -- let's just have one intrinsic and leave it up to the LLVM backend to decide how to lower that.

Suggested by `@hanna-kruppe` in rust-lang/rust#136459; Cc `@tgross35`

try-job: test-various

Author: tgross35

src/intrinsics/mod.rs

@@ -145,60 +145,60 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 this.write_scalar(Scalar::from_bool(branch), dest)?;
             }
 
-            "floorf16" | "ceilf16" | "truncf16" | "roundf16" | "rintf16" => {
+            "floorf16" | "ceilf16" | "truncf16" | "roundf16" | "round_ties_even_f16" => {
                 let [f] = check_arg_count(args)?;
                 let f = this.read_scalar(f)?.to_f16()?;
                 let mode = match intrinsic_name {
                     "floorf16" => Round::TowardNegative,
                     "ceilf16" => Round::TowardPositive,
                     "truncf16" => Round::TowardZero,
                     "roundf16" => Round::NearestTiesToAway,
-                    "rintf16" => Round::NearestTiesToEven,
+                    "round_ties_even_f16" => Round::NearestTiesToEven,
                     _ => bug!(),
                 };
                 let res = f.round_to_integral(mode).value;
                 let res = this.adjust_nan(res, &[f]);
                 this.write_scalar(res, dest)?;
             }
-            "floorf32" | "ceilf32" | "truncf32" | "roundf32" | "rintf32" => {
+            "floorf32" | "ceilf32" | "truncf32" | "roundf32" | "round_ties_even_f32" => {
                 let [f] = check_arg_count(args)?;
                 let f = this.read_scalar(f)?.to_f32()?;
                 let mode = match intrinsic_name {
                     "floorf32" => Round::TowardNegative,
                     "ceilf32" => Round::TowardPositive,
                     "truncf32" => Round::TowardZero,
                     "roundf32" => Round::NearestTiesToAway,
-                    "rintf32" => Round::NearestTiesToEven,
+                    "round_ties_even_f32" => Round::NearestTiesToEven,
                     _ => bug!(),
                 };
                 let res = f.round_to_integral(mode).value;
                 let res = this.adjust_nan(res, &[f]);
                 this.write_scalar(res, dest)?;
             }
-            "floorf64" | "ceilf64" | "truncf64" | "roundf64" | "rintf64" => {
+            "floorf64" | "ceilf64" | "truncf64" | "roundf64" | "round_ties_even_f64" => {
                 let [f] = check_arg_count(args)?;
                 let f = this.read_scalar(f)?.to_f64()?;
                 let mode = match intrinsic_name {
                     "floorf64" => Round::TowardNegative,
                     "ceilf64" => Round::TowardPositive,
                     "truncf64" => Round::TowardZero,
                     "roundf64" => Round::NearestTiesToAway,
-                    "rintf64" => Round::NearestTiesToEven,
+                    "round_ties_even_f64" => Round::NearestTiesToEven,
                     _ => bug!(),
                 };
                 let res = f.round_to_integral(mode).value;
                 let res = this.adjust_nan(res, &[f]);
                 this.write_scalar(res, dest)?;
             }
-            "floorf128" | "ceilf128" | "truncf128" | "roundf128" | "rintf128" => {
+            "floorf128" | "ceilf128" | "truncf128" | "roundf128" | "round_ties_even_f128" => {
                 let [f] = check_arg_count(args)?;
                 let f = this.read_scalar(f)?.to_f128()?;
                 let mode = match intrinsic_name {
                     "floorf128" => Round::TowardNegative,
                     "ceilf128" => Round::TowardPositive,
                     "truncf128" => Round::TowardZero,
                     "roundf128" => Round::NearestTiesToAway,
-                    "rintf128" => Round::NearestTiesToEven,
+                    "round_ties_even_f128" => Round::NearestTiesToEven,
                     _ => bug!(),
                 };
                 let res = f.round_to_integral(mode).value;