Auto merge of #9581 - ebobrow:mul-add-negative, r=Manishearth

`suboptimal_flops` lint for multiply and subtract

fixes #9526

changelog: [`suboptimal_flops`] lint for multiply and subtract

7 files changed, 81 insertions, 25 deletions

diff --git a/clippy_lints/src/floating_point_arithmetic.rs b/clippy_lints/src/floating_point_arithmetic.rs
index e71afec12a7..0ed30196475 100644
--- a/clippy_lints/src/floating_point_arithmetic.rs
+++ b/clippy_lints/src/floating_point_arithmetic.rs
@@ -311,7 +311,8 @@ fn check_powi(cx: &LateContext<'_>, expr: &Expr<'_>, receiver: &Expr<'_>, args:
 
                 if let ExprKind::Binary(
                     Spanned {
-                        node: BinOpKind::Add, ..
+                        node: op @ (BinOpKind::Add | BinOpKind::Sub),
+                        ..
                     },
                     lhs,
                     rhs,
@@ -319,6 +320,16 @@ fn check_powi(cx: &LateContext<'_>, expr: &Expr<'_>, receiver: &Expr<'_>, args:
                 {
                     let other_addend = if lhs.hir_id == expr.hir_id { rhs } else { lhs };
 
+                    // Negate expr if original code has subtraction and expr is on the right side
+                    let maybe_neg_sugg = |expr, hir_id| {
+                        let sugg = Sugg::hir(cx, expr, "..");
+                        if matches!(op, BinOpKind::Sub) && hir_id == rhs.hir_id {
+                            format!("-{sugg}")
+                        } else {
+                            sugg.to_string()
+                        }
+                    };
+
                     span_lint_and_sugg(
                         cx,
                         SUBOPTIMAL_FLOPS,
@@ -328,8 +339,8 @@ fn check_powi(cx: &LateContext<'_>, expr: &Expr<'_>, receiver: &Expr<'_>, args:
                         format!(
                             "{}.mul_add({}, {})",
                             Sugg::hir(cx, receiver, "..").maybe_par(),
-                            Sugg::hir(cx, receiver, ".."),
-                            Sugg::hir(cx, other_addend, ".."),
+                            maybe_neg_sugg(receiver, expr.hir_id),
+                            maybe_neg_sugg(other_addend, other_addend.hir_id),
                         ),
                         Applicability::MachineApplicable,
                     );
@@ -443,7 +454,8 @@ fn is_float_mul_expr<'a>(cx: &LateContext<'_>, expr: &'a Expr<'a>) -> Option<(&'
 fn check_mul_add(cx: &LateContext<'_>, expr: &Expr<'_>) {
     if let ExprKind::Binary(
         Spanned {
-            node: BinOpKind::Add, ..
+            node: op @ (BinOpKind::Add | BinOpKind::Sub),
+            ..
         },
         lhs,
         rhs,
@@ -457,10 +469,27 @@ fn check_mul_add(cx: &LateContext<'_>, expr: &Expr<'_>) {
             }
         }
 
+        let maybe_neg_sugg = |expr| {
+            let sugg = Sugg::hir(cx, expr, "..");
+            if let BinOpKind::Sub = op {
+                format!("-{sugg}")
+            } else {
+                sugg.to_string()
+            }
+        };
+
         let (recv, arg1, arg2) = if let Some((inner_lhs, inner_rhs)) = is_float_mul_expr(cx, lhs) {
-            (inner_lhs, inner_rhs, rhs)
+            (
+                inner_lhs,
+                Sugg::hir(cx, inner_rhs, "..").to_string(),
+                maybe_neg_sugg(rhs),
+            )
         } else if let Some((inner_lhs, inner_rhs)) = is_float_mul_expr(cx, rhs) {
-            (inner_lhs, inner_rhs, lhs)
+            (
+                inner_lhs,
+                maybe_neg_sugg(inner_rhs),
+                Sugg::hir(cx, lhs, "..").to_string(),
+            )
         } else {
             return;
         };
@@ -471,12 +500,7 @@ fn check_mul_add(cx: &LateContext<'_>, expr: &Expr<'_>) {
             expr.span,
             "multiply and add expressions can be calculated more efficiently and accurately",
             "consider using",
-            format!(
-                "{}.mul_add({}, {})",
-                prepare_receiver_sugg(cx, recv),
-                Sugg::hir(cx, arg1, ".."),
-                Sugg::hir(cx, arg2, ".."),
-            ),
+            format!("{}.mul_add({arg1}, {arg2})", prepare_receiver_sugg(cx, recv)),
             Applicability::MachineApplicable,
         );
     }
diff --git a/tests/ui/floating_point_mul_add.fixed b/tests/ui/floating_point_mul_add.fixed
index 169ec02f82b..d3e536ba350 100644
--- a/tests/ui/floating_point_mul_add.fixed
+++ b/tests/ui/floating_point_mul_add.fixed
@@ -19,7 +19,9 @@ fn main() {
     let d: f64 = 0.0001;
 
     let _ = a.mul_add(b, c);
+    let _ = a.mul_add(b, -c);
     let _ = a.mul_add(b, c);
+    let _ = a.mul_add(-b, c);
     let _ = 2.0f64.mul_add(4.0, a);
     let _ = 2.0f64.mul_add(4., a);
 
diff --git a/tests/ui/floating_point_mul_add.rs b/tests/ui/floating_point_mul_add.rs
index 5338d4fc2b7..5d4a9e35cfc 100644
--- a/tests/ui/floating_point_mul_add.rs
+++ b/tests/ui/floating_point_mul_add.rs
@@ -19,7 +19,9 @@ fn main() {
     let d: f64 = 0.0001;
 
     let _ = a * b + c;
+    let _ = a * b - c;
     let _ = c + a * b;
+    let _ = c - a * b;
     let _ = a + 2.0 * 4.0;
     let _ = a + 2. * 4.;
 
diff --git a/tests/ui/floating_point_mul_add.stderr b/tests/ui/floating_point_mul_add.stderr
index e637bbf90ca..a79ae94e8d4 100644
--- a/tests/ui/floating_point_mul_add.stderr
+++ b/tests/ui/floating_point_mul_add.stderr
@@ -9,56 +9,68 @@ LL |     let _ = a * b + c;
 error: multiply and add expressions can be calculated more efficiently and accurately
   --> $DIR/floating_point_mul_add.rs:22:13
    |
+LL |     let _ = a * b - c;
+   |             ^^^^^^^^^ help: consider using: `a.mul_add(b, -c)`
+
+error: multiply and add expressions can be calculated more efficiently and accurately
+  --> $DIR/floating_point_mul_add.rs:23:13
+   |
 LL |     let _ = c + a * b;
    |             ^^^^^^^^^ help: consider using: `a.mul_add(b, c)`
 
 error: multiply and add expressions can be calculated more efficiently and accurately
-  --> $DIR/floating_point_mul_add.rs:23:13
+  --> $DIR/floating_point_mul_add.rs:24:13
+   |
+LL |     let _ = c - a * b;
+   |             ^^^^^^^^^ help: consider using: `a.mul_add(-b, c)`
+
+error: multiply and add expressions can be calculated more efficiently and accurately
+  --> $DIR/floating_point_mul_add.rs:25:13
    |
 LL |     let _ = a + 2.0 * 4.0;
    |             ^^^^^^^^^^^^^ help: consider using: `2.0f64.mul_add(4.0, a)`
 
 error: multiply and add expressions can be calculated more efficiently and accurately
-  --> $DIR/floating_point_mul_add.rs:24:13
+  --> $DIR/floating_point_mul_add.rs:26:13
    |
 LL |     let _ = a + 2. * 4.;
    |             ^^^^^^^^^^^ help: consider using: `2.0f64.mul_add(4., a)`
 
 error: multiply and add expressions can be calculated more efficiently and accurately
-  --> $DIR/floating_point_mul_add.rs:26:13
+  --> $DIR/floating_point_mul_add.rs:28:13
    |
 LL |     let _ = (a * b) + c;
    |             ^^^^^^^^^^^ help: consider using: `a.mul_add(b, c)`
 
 error: multiply and add expressions can be calculated more efficiently and accurately
-  --> $DIR/floating_point_mul_add.rs:27:13
+  --> $DIR/floating_point_mul_add.rs:29:13
    |
 LL |     let _ = c + (a * b);
    |             ^^^^^^^^^^^ help: consider using: `a.mul_add(b, c)`
 
 error: multiply and add expressions can be calculated more efficiently and accurately
-  --> $DIR/floating_point_mul_add.rs:28:13
+  --> $DIR/floating_point_mul_add.rs:30:13
    |
 LL |     let _ = a * b * c + d;
    |             ^^^^^^^^^^^^^ help: consider using: `(a * b).mul_add(c, d)`
 
 error: multiply and add expressions can be calculated more efficiently and accurately
-  --> $DIR/floating_point_mul_add.rs:30:13
+  --> $DIR/floating_point_mul_add.rs:32:13
    |
 LL |     let _ = a.mul_add(b, c) * a.mul_add(b, c) + a.mul_add(b, c) + c;
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `a.mul_add(b, c).mul_add(a.mul_add(b, c), a.mul_add(b, c))`
 
 error: multiply and add expressions can be calculated more efficiently and accurately
-  --> $DIR/floating_point_mul_add.rs:31:13
+  --> $DIR/floating_point_mul_add.rs:33:13
    |
 LL |     let _ = 1234.567_f64 * 45.67834_f64 + 0.0004_f64;
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `1234.567_f64.mul_add(45.67834_f64, 0.0004_f64)`
 
 error: multiply and add expressions can be calculated more efficiently and accurately
-  --> $DIR/floating_point_mul_add.rs:33:13
+  --> $DIR/floating_point_mul_add.rs:35:13
    |
 LL |     let _ = (a * a + b).sqrt();
    |             ^^^^^^^^^^^ help: consider using: `a.mul_add(a, b)`
 
-error: aborting due to 10 previous errors
+error: aborting due to 12 previous errors
 
diff --git a/tests/ui/floating_point_powi.fixed b/tests/ui/floating_point_powi.fixed
index 68c81316930..884d05fed71 100644
--- a/tests/ui/floating_point_powi.fixed
+++ b/tests/ui/floating_point_powi.fixed
@@ -8,7 +8,9 @@ fn main() {
 
     let y = 4f32;
     let _ = x.mul_add(x, y);
+    let _ = x.mul_add(x, -y);
     let _ = y.mul_add(y, x);
+    let _ = y.mul_add(-y, x);
     let _ = (y as f32).mul_add(y as f32, x);
     let _ = x.mul_add(x, y).sqrt();
     let _ = y.mul_add(y, x).sqrt();
diff --git a/tests/ui/floating_point_powi.rs b/tests/ui/floating_point_powi.rs
index 96101a487ee..e6a1c895371 100644
--- a/tests/ui/floating_point_powi.rs
+++ b/tests/ui/floating_point_powi.rs
@@ -8,7 +8,9 @@ fn main() {
 
     let y = 4f32;
     let _ = x.powi(2) + y;
+    let _ = x.powi(2) - y;
     let _ = x + y.powi(2);
+    let _ = x - y.powi(2);
     let _ = x + (y as f32).powi(2);
     let _ = (x.powi(2) + y).sqrt();
     let _ = (x + y.powi(2)).sqrt();
diff --git a/tests/ui/floating_point_powi.stderr b/tests/ui/floating_point_powi.stderr
index a651954a5f8..5df0de1fef2 100644
--- a/tests/ui/floating_point_powi.stderr
+++ b/tests/ui/floating_point_powi.stderr
@@ -9,26 +9,38 @@ LL |     let _ = x.powi(2) + y;
 error: multiply and add expressions can be calculated more efficiently and accurately
   --> $DIR/floating_point_powi.rs:11:13
    |
+LL |     let _ = x.powi(2) - y;
+   |             ^^^^^^^^^^^^^ help: consider using: `x.mul_add(x, -y)`
+
+error: multiply and add expressions can be calculated more efficiently and accurately
+  --> $DIR/floating_point_powi.rs:12:13
+   |
 LL |     let _ = x + y.powi(2);
    |             ^^^^^^^^^^^^^ help: consider using: `y.mul_add(y, x)`
 
 error: multiply and add expressions can be calculated more efficiently and accurately
-  --> $DIR/floating_point_powi.rs:12:13
+  --> $DIR/floating_point_powi.rs:13:13
+   |
+LL |     let _ = x - y.powi(2);
+   |             ^^^^^^^^^^^^^ help: consider using: `y.mul_add(-y, x)`
+
+error: multiply and add expressions can be calculated more efficiently and accurately
+  --> $DIR/floating_point_powi.rs:14:13
    |
 LL |     let _ = x + (y as f32).powi(2);
    |             ^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `(y as f32).mul_add(y as f32, x)`
 
 error: multiply and add expressions can be calculated more efficiently and accurately
-  --> $DIR/floating_point_powi.rs:13:13
+  --> $DIR/floating_point_powi.rs:15:13
    |
 LL |     let _ = (x.powi(2) + y).sqrt();
    |             ^^^^^^^^^^^^^^^ help: consider using: `x.mul_add(x, y)`
 
 error: multiply and add expressions can be calculated more efficiently and accurately
-  --> $DIR/floating_point_powi.rs:14:13
+  --> $DIR/floating_point_powi.rs:16:13
    |
 LL |     let _ = (x + y.powi(2)).sqrt();
    |             ^^^^^^^^^^^^^^^ help: consider using: `y.mul_add(y, x)`
 
-error: aborting due to 5 previous errors
+error: aborting due to 7 previous errors