Dont suggest suboptimal_flops unavailable in nostd

Fixes #10634

Author: lukaslueg

clippy_lints/src/floating_point_arithmetic.rs

@@ -2,9 +2,10 @@ use clippy_utils::consts::{
     constant, constant_simple, Constant,
     Constant::{Int, F32, F64},
 };
-use clippy_utils::diagnostics::span_lint_and_sugg;
-use clippy_utils::higher;
-use clippy_utils::{eq_expr_value, get_parent_expr, in_constant, numeric_literal, peel_blocks, sugg};
+use clippy_utils::{
+    diagnostics::span_lint_and_sugg, eq_expr_value, get_parent_expr, higher, in_constant, is_no_std_crate,
+    numeric_literal, peel_blocks, sugg,
+};
 use if_chain::if_chain;
 use rustc_errors::Applicability;
 use rustc_hir::{BinOpKind, Expr, ExprKind, PathSegment, UnOp};
@@ -452,6 +453,9 @@ fn is_float_mul_expr<'a>(cx: &LateContext<'_>, expr: &'a Expr<'a>) -> Option<(&'
 
 // TODO: Fix rust-lang/rust-clippy#4735
 fn check_mul_add(cx: &LateContext<'_>, expr: &Expr<'_>) {
+    if is_no_std_crate(cx) {
+        return; // The suggested methods are not available in core
+    }
     if let ExprKind::Binary(
         Spanned {
             node: op @ (BinOpKind::Add | BinOpKind::Sub),
@@ -566,6 +570,9 @@ fn are_negated<'a>(cx: &LateContext<'_>, expr1: &'a Expr<'a>, expr2: &'a Expr<'a
 }
 
 fn check_custom_abs(cx: &LateContext<'_>, expr: &Expr<'_>) {
+    if is_no_std_crate(cx) {
+        return; // The suggested methods are not available in core
+    }
     if_chain! {
         if let Some(higher::If { cond, then, r#else: Some(r#else) }) = higher::If::hir(expr);
         let if_body_expr = peel_blocks(then);

tests/ui/floating_point_arithmetic_nostd.rs

@@ -0,0 +1,31 @@
+#![feature(lang_items, start)]
+#![warn(clippy::imprecise_flops)]
+#![warn(clippy::suboptimal_flops)]
+#![no_std]
+
+// The following should not lint, as the suggested methods {f32,f64}.mul_add()
+// and {f32,f64}::abs() are not available in no_std
+
+pub fn mul_add() {
+    let a: f64 = 1234.567;
+    let b: f64 = 45.67834;
+    let c: f64 = 0.0004;
+    let _ = a * b + c;
+}
+
+fn fake_abs1(num: f64) -> f64 {
+    if num >= 0.0 { num } else { -num }
+}
+
+#[start]
+fn main(_argc: isize, _argv: *const *const u8) -> isize {
+    0
+}
+
+#[panic_handler]
+fn panic(_info: &core::panic::PanicInfo) -> ! {
+    loop {}
+}
+
+#[lang = "eh_personality"]
+extern "C" fn eh_personality() {}