Auto merge of rust-lang#5702 - ebroto:5698_mul_not_comm, r=matthiaskrgr

if_same_then_else: don't assume multiplication is always commutative

changelog: Don't assume multiplication is always commutative in [`if_same_then_else`]

Fixes rust-lang#5698

clippy_lints/src/utils/hir_utils.rs

@@ -309,18 +309,15 @@ fn swap_binop<'a>(
     rhs: &'a Expr<'a>,
 ) -> Option<(BinOpKind, &'a Expr<'a>, &'a Expr<'a>)> {
     match binop {
-        BinOpKind::Add
-        | BinOpKind::Mul
-        | BinOpKind::Eq
-        | BinOpKind::Ne
-        | BinOpKind::BitAnd
-        | BinOpKind::BitXor
-        | BinOpKind::BitOr => Some((binop, rhs, lhs)),
+        BinOpKind::Add | BinOpKind::Eq | BinOpKind::Ne | BinOpKind::BitAnd | BinOpKind::BitXor | BinOpKind::BitOr => {
+            Some((binop, rhs, lhs))
+        },
         BinOpKind::Lt => Some((BinOpKind::Gt, rhs, lhs)),
         BinOpKind::Le => Some((BinOpKind::Ge, rhs, lhs)),
         BinOpKind::Ge => Some((BinOpKind::Le, rhs, lhs)),
         BinOpKind::Gt => Some((BinOpKind::Lt, rhs, lhs)),
-        BinOpKind::Shl
+        BinOpKind::Mul // Not always commutative, e.g. with matrices. See issue #5698
+        | BinOpKind::Shl
         | BinOpKind::Shr
         | BinOpKind::Rem
         | BinOpKind::Sub

tests/ui/if_same_then_else.rs

@@ -142,4 +142,16 @@ fn func() {
 
 fn f(val: &[u8]) {}
 
+mod issue_5698 {
+    fn mul_not_always_commutative(x: i32, y: i32) -> i32 {
+        if x == 42 {
+            x * y
+        } else if x == 21 {
+            y * x
+        } else {
+            0
+        }
+    }
+}
+
 fn main() {}