Rollup merge of rust-lang#5443 - thiagoarrais:issue-2040, r=flip1995

Some accuracy lints for floating point operations

This will add some lints for accuracy on floating point operations suggested by @clarfon in rust-lang#2040 (fixes rust-lang#2040).

These are the remaining lints:

- [x] x.powi(2) => x * x
- [x] x.logN() / y.logN() => x.logbase(y)
- [x] x.logbase(E) => x.log()
- [x] x.logbase(10) => x.log10()
- [x] x.logbase(2) => x.log2().
- [x] x * PI / 180 => x.to_radians()
- [x] x * 180 / PI => x.to_degrees()
- [x] (x + 1).log() => x.log_1p()
- [x] sqrt(x * x + y * y) => x.hypot(y)

changelog: Included some accuracy lints for floating point operations

clippy_lints/src/floating_point_arithmetic.rs

@@ -1,11 +1,11 @@
 use crate::consts::{
     constant, constant_simple, Constant,
-    Constant::{F32, F64},
+    Constant::{Int, F32, F64},
 };
-use crate::utils::{higher, numeric_literal, span_lint_and_sugg, sugg, SpanlessEq};
+use crate::utils::{get_parent_expr, higher, numeric_literal, span_lint_and_sugg, sugg, SpanlessEq};
 use if_chain::if_chain;
 use rustc_errors::Applicability;
-use rustc_hir::{BinOpKind, Expr, ExprKind, UnOp};
+use rustc_hir::{BinOpKind, Expr, ExprKind, PathSegment, UnOp};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::ty;
 use rustc_session::{declare_lint_pass, declare_tool_lint};
@@ -293,6 +293,121 @@ fn check_powf(cx: &LateContext<'_>, expr: &Expr<'_>, args: &[Expr<'_>]) {
     }
 }
 
+fn check_powi(cx: &LateContext<'_>, expr: &Expr<'_>, args: &[Expr<'_>]) {
+    if let Some((value, _)) = constant(cx, cx.tables(), &args[1]) {
+        if value == Int(2) {
+            if let Some(parent) = get_parent_expr(cx, expr) {
+                if let Some(grandparent) = get_parent_expr(cx, parent) {
+                    if let ExprKind::MethodCall(PathSegment { ident: method_name, .. }, _, args, _) = grandparent.kind {
+                        if method_name.as_str() == "sqrt" && detect_hypot(cx, args).is_some() {
+                            return;
+                        }
+                    }
+                }
+
+                if let ExprKind::Binary(
+                    Spanned {
+                        node: BinOpKind::Add, ..
+                    },
+                    ref lhs,
+                    ref rhs,
+                ) = parent.kind
+                {
+                    let other_addend = if lhs.hir_id == expr.hir_id { rhs } else { lhs };
+
+                    span_lint_and_sugg(
+                        cx,
+                        SUBOPTIMAL_FLOPS,
+                        parent.span,
+                        "square can be computed more efficiently",
+                        "consider using",
+                        format!(
+                            "{}.mul_add({}, {})",
+                            Sugg::hir(cx, &args[0], ".."),
+                            Sugg::hir(cx, &args[0], ".."),
+                            Sugg::hir(cx, &other_addend, ".."),
+                        ),
+                        Applicability::MachineApplicable,
+                    );
+
+                    return;
+                }
+            }
+
+            span_lint_and_sugg(
+                cx,
+                SUBOPTIMAL_FLOPS,
+                expr.span,
+                "square can be computed more efficiently",
+                "consider using",
+                format!("{} * {}", Sugg::hir(cx, &args[0], ".."), Sugg::hir(cx, &args[0], "..")),
+                Applicability::MachineApplicable,
+            );
+        }
+    }
+}
+
+fn detect_hypot(cx: &LateContext<'_>, args: &[Expr<'_>]) -> Option<String> {
+    if let ExprKind::Binary(
+        Spanned {
+            node: BinOpKind::Add, ..
+        },
+        ref add_lhs,
+        ref add_rhs,
+    ) = args[0].kind
+    {
+        // check if expression of the form x * x + y * y
+        if_chain! {
+            if let ExprKind::Binary(Spanned { node: BinOpKind::Mul, .. }, ref lmul_lhs, ref lmul_rhs) = add_lhs.kind;
+            if let ExprKind::Binary(Spanned { node: BinOpKind::Mul, .. }, ref rmul_lhs, ref rmul_rhs) = add_rhs.kind;
+            if are_exprs_equal(cx, lmul_lhs, lmul_rhs);
+            if are_exprs_equal(cx, rmul_lhs, rmul_rhs);
+            then {
+                return Some(format!("{}.hypot({})", Sugg::hir(cx, &lmul_lhs, ".."), Sugg::hir(cx, &rmul_lhs, "..")));
+            }
+        }
+
+        // check if expression of the form x.powi(2) + y.powi(2)
+        if_chain! {
+            if let ExprKind::MethodCall(
+                PathSegment { ident: lmethod_name, .. },
+                ref _lspan,
+                ref largs,
+                _
+            ) = add_lhs.kind;
+            if let ExprKind::MethodCall(
+                PathSegment { ident: rmethod_name, .. },
+                ref _rspan,
+                ref rargs,
+                _
+            ) = add_rhs.kind;
+            if lmethod_name.as_str() == "powi" && rmethod_name.as_str() == "powi";
+            if let Some((lvalue, _)) = constant(cx, cx.tables(), &largs[1]);
+            if let Some((rvalue, _)) = constant(cx, cx.tables(), &rargs[1]);
+            if Int(2) == lvalue && Int(2) == rvalue;
+            then {
+                return Some(format!("{}.hypot({})", Sugg::hir(cx, &largs[0], ".."), Sugg::hir(cx, &rargs[0], "..")));
+            }
+        }
+    }
+
+    None
+}
+
+fn check_hypot(cx: &LateContext<'_>, expr: &Expr<'_>, args: &[Expr<'_>]) {
+    if let Some(message) = detect_hypot(cx, args) {
+        span_lint_and_sugg(
+            cx,
+            IMPRECISE_FLOPS,
+            expr.span,
+            "hypotenuse can be computed more accurately",
+            "consider using",
+            message,
+            Applicability::MachineApplicable,
+        );
+    }
+}
+
 // TODO: Lint expressions of the form `x.exp() - y` where y > 1
 // and suggest usage of `x.exp_m1() - (y - 1)` instead
 fn check_expm1(cx: &LateContext<'_>, expr: &Expr<'_>) {
@@ -344,6 +459,14 @@ fn check_mul_add(cx: &LateContext<'_>, expr: &Expr<'_>) {
         rhs,
     ) = &expr.kind
     {
+        if let Some(parent) = get_parent_expr(cx, expr) {
+            if let ExprKind::MethodCall(PathSegment { ident: method_name, .. }, _, args, _) = parent.kind {
+                if method_name.as_str() == "sqrt" && detect_hypot(cx, args).is_some() {
+                    return;
+                }
+            }
+        }
+
         let (recv, arg1, arg2) = if let Some((inner_lhs, inner_rhs)) = is_float_mul_expr(cx, lhs) {
             (inner_lhs, inner_rhs, rhs)
         } else if let Some((inner_lhs, inner_rhs)) = is_float_mul_expr(cx, rhs) {
@@ -479,6 +602,100 @@ fn check_custom_abs(cx: &LateContext<'_>, expr: &Expr<'_>) {
     }
 }
 
+fn are_same_base_logs(cx: &LateContext<'_>, expr_a: &Expr<'_>, expr_b: &Expr<'_>) -> bool {
+    if_chain! {
+        if let ExprKind::MethodCall(PathSegment { ident: method_name_a, .. }, _, ref args_a, _) = expr_a.kind;
+        if let ExprKind::MethodCall(PathSegment { ident: method_name_b, .. }, _, ref args_b, _) = expr_b.kind;
+        then {
+            return method_name_a.as_str() == method_name_b.as_str() &&
+                args_a.len() == args_b.len() &&
+                (
+                    ["ln", "log2", "log10"].contains(&&*method_name_a.as_str()) ||
+                    method_name_a.as_str() == "log" && args_a.len() == 2 && are_exprs_equal(cx, &args_a[1], &args_b[1])
+                );
+        }
+    }
+
+    false
+}
+
+fn check_log_division(cx: &LateContext<'_>, expr: &Expr<'_>) {
+    // check if expression of the form x.logN() / y.logN()
+    if_chain! {
+        if let ExprKind::Binary(
+            Spanned {
+                node: BinOpKind::Div, ..
+            },
+            lhs,
+            rhs,
+        ) = &expr.kind;
+        if are_same_base_logs(cx, lhs, rhs);
+        if let ExprKind::MethodCall(_, _, ref largs, _) = lhs.kind;
+        if let ExprKind::MethodCall(_, _, ref rargs, _) = rhs.kind;
+        then {
+            span_lint_and_sugg(
+                cx,
+                SUBOPTIMAL_FLOPS,
+                expr.span,
+                "log base can be expressed more clearly",
+                "consider using",
+                format!("{}.log({})", Sugg::hir(cx, &largs[0], ".."), Sugg::hir(cx, &rargs[0], ".."),),
+                Applicability::MachineApplicable,
+            );
+        }
+    }
+}
+
+fn check_radians(cx: &LateContext<'_>, expr: &Expr<'_>) {
+    if_chain! {
+        if let ExprKind::Binary(
+            Spanned {
+                node: BinOpKind::Div, ..
+            },
+            div_lhs,
+            div_rhs,
+        ) = &expr.kind;
+        if let ExprKind::Binary(
+            Spanned {
+                node: BinOpKind::Mul, ..
+            },
+            mul_lhs,
+            mul_rhs,
+        ) = &div_lhs.kind;
+        if let Some((rvalue, _)) = constant(cx, cx.tables(), div_rhs);
+        if let Some((lvalue, _)) = constant(cx, cx.tables(), mul_rhs);
+        then {
+            // TODO: also check for constant values near PI/180 or 180/PI
+            if (F32(f32_consts::PI) == rvalue || F64(f64_consts::PI) == rvalue) &&
+               (F32(180_f32) == lvalue || F64(180_f64) == lvalue)
+            {
+                span_lint_and_sugg(
+                    cx,
+                    SUBOPTIMAL_FLOPS,
+                    expr.span,
+                    "conversion to degrees can be done more accurately",
+                    "consider using",
+                    format!("{}.to_degrees()", Sugg::hir(cx, &mul_lhs, "..")),
+                    Applicability::MachineApplicable,
+                );
+            } else if
+                (F32(180_f32) == rvalue || F64(180_f64) == rvalue) &&
+                (F32(f32_consts::PI) == lvalue || F64(f64_consts::PI) == lvalue)
+            {
+                span_lint_and_sugg(
+                    cx,
+                    SUBOPTIMAL_FLOPS,
+                    expr.span,
+                    "conversion to radians can be done more accurately",
+                    "consider using",
+                    format!("{}.to_radians()", Sugg::hir(cx, &mul_lhs, "..")),
+                    Applicability::MachineApplicable,
+                );
+            }
+        }
+    }
+}
+
 impl<'tcx> LateLintPass<'tcx> for FloatingPointArithmetic {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
         if let ExprKind::MethodCall(ref path, _, args, _) = &expr.kind {
@@ -489,13 +706,17 @@ impl<'tcx> LateLintPass<'tcx> for FloatingPointArithmetic {
                     "ln" => check_ln1p(cx, expr, args),
                     "log" => check_log_base(cx, expr, args),
                     "powf" => check_powf(cx, expr, args),
+                    "powi" => check_powi(cx, expr, args),
+                    "sqrt" => check_hypot(cx, expr, args),
                     _ => {},
                 }
             }
         } else {
             check_expm1(cx, expr);
             check_mul_add(cx, expr);
             check_custom_abs(cx, expr);
+            check_log_division(cx, expr);
+            check_radians(cx, expr);
         }
     }
 }

tests/ui/floating_point_hypot.fixed

@@ -0,0 +1,14 @@
+// run-rustfix
+#![warn(clippy::imprecise_flops)]
+
+fn main() {
+    let x = 3f32;
+    let y = 4f32;
+    let _ = x.hypot(y);
+    let _ = (x + 1f32).hypot(y);
+    let _ = x.hypot(y);
+    // Cases where the lint shouldn't be applied
+    // TODO: linting this adds some complexity, but could be done
+    let _ = x.mul_add(x, y * y).sqrt();
+    let _ = (x * 4f32 + y * y).sqrt();
+}

tests/ui/floating_point_hypot.rs

@@ -0,0 +1,14 @@
+// run-rustfix
+#![warn(clippy::imprecise_flops)]
+
+fn main() {
+    let x = 3f32;
+    let y = 4f32;
+    let _ = (x * x + y * y).sqrt();
+    let _ = ((x + 1f32) * (x + 1f32) + y * y).sqrt();
+    let _ = (x.powi(2) + y.powi(2)).sqrt();
+    // Cases where the lint shouldn't be applied
+    // TODO: linting this adds some complexity, but could be done
+    let _ = x.mul_add(x, y * y).sqrt();
+    let _ = (x * 4f32 + y * y).sqrt();
+}

tests/ui/floating_point_hypot.stderr

@@ -0,0 +1,22 @@
+error: hypotenuse can be computed more accurately
+  --> $DIR/floating_point_hypot.rs:7:13
+   |
+LL |     let _ = (x * x + y * y).sqrt();
+   |             ^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `x.hypot(y)`
+   |
+   = note: `-D clippy::imprecise-flops` implied by `-D warnings`
+
+error: hypotenuse can be computed more accurately
+  --> $DIR/floating_point_hypot.rs:8:13
+   |
+LL |     let _ = ((x + 1f32) * (x + 1f32) + y * y).sqrt();
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `(x + 1f32).hypot(y)`
+
+error: hypotenuse can be computed more accurately
+  --> $DIR/floating_point_hypot.rs:9:13
+   |
+LL |     let _ = (x.powi(2) + y.powi(2)).sqrt();
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `x.hypot(y)`
+
+error: aborting due to 3 previous errors
+

tests/ui/floating_point_log.fixed

@@ -25,11 +25,11 @@ fn check_ln1p() {
     let _ = 2.0f32.ln_1p();
     let _ = x.ln_1p();
     let _ = (x / 2.0).ln_1p();
-    let _ = x.powi(2).ln_1p();
-    let _ = (x.powi(2) / 2.0).ln_1p();
+    let _ = x.powi(3).ln_1p();
+    let _ = (x.powi(3) / 2.0).ln_1p();
     let _ = ((std::f32::consts::E - 1.0)).ln_1p();
     let _ = x.ln_1p();
-    let _ = x.powi(2).ln_1p();
+    let _ = x.powi(3).ln_1p();
     let _ = (x + 2.0).ln_1p();
     let _ = (x / 2.0).ln_1p();
     // Cases where the lint shouldn't be applied
@@ -43,9 +43,9 @@ fn check_ln1p() {
     let _ = 2.0f64.ln_1p();
     let _ = x.ln_1p();
     let _ = (x / 2.0).ln_1p();
-    let _ = x.powi(2).ln_1p();
+    let _ = x.powi(3).ln_1p();
     let _ = x.ln_1p();
-    let _ = x.powi(2).ln_1p();
+    let _ = x.powi(3).ln_1p();
     let _ = (x + 2.0).ln_1p();
     let _ = (x / 2.0).ln_1p();
     // Cases where the lint shouldn't be applied

tests/ui/floating_point_log.rs

@@ -25,11 +25,11 @@ fn check_ln1p() {
     let _ = (1f32 + 2.0).ln();
     let _ = (1.0 + x).ln();
     let _ = (1.0 + x / 2.0).ln();
-    let _ = (1.0 + x.powi(2)).ln();
-    let _ = (1.0 + x.powi(2) / 2.0).ln();
+    let _ = (1.0 + x.powi(3)).ln();
+    let _ = (1.0 + x.powi(3) / 2.0).ln();
     let _ = (1.0 + (std::f32::consts::E - 1.0)).ln();
     let _ = (x + 1.0).ln();
-    let _ = (x.powi(2) + 1.0).ln();
+    let _ = (x.powi(3) + 1.0).ln();
     let _ = (x + 2.0 + 1.0).ln();
     let _ = (x / 2.0 + 1.0).ln();
     // Cases where the lint shouldn't be applied
@@ -43,9 +43,9 @@ fn check_ln1p() {
     let _ = (1f64 + 2.0).ln();
     let _ = (1.0 + x).ln();
     let _ = (1.0 + x / 2.0).ln();
-    let _ = (1.0 + x.powi(2)).ln();
+    let _ = (1.0 + x.powi(3)).ln();
     let _ = (x + 1.0).ln();
-    let _ = (x.powi(2) + 1.0).ln();
+    let _ = (x.powi(3) + 1.0).ln();
     let _ = (x + 2.0 + 1.0).ln();
     let _ = (x / 2.0 + 1.0).ln();
     // Cases where the lint shouldn't be applied