Auto merge of rust-lang#89459 - tspiteri:idiv-overflow-bitand, r=kennytm

Use bitand when checking for signed integer division overflow For `self == Self::MIN && rhs == -1`, LLVM does not realize that this is the same check made by `self / rhs`, so the code generated may have some unnecessary duplication. For `(self == Self::MIN) & (rhs == -1)`, LLVM realizes it is the same check.
rust-lang-ci · Oct 3, 2021 · 4479cb8 · 4479cb8
2 parents c24c906 + 1139ee3
commit 4479cb8
Showing 1 changed file with 16 additions and 8 deletions.
diff --git a/library/core/src/num/int_macros.rs b/library/core/src/num/int_macros.rs
@@ -543,7 +543,8 @@ macro_rules! int_impl {
                       without modifying the original"]
         #[inline]
         pub const fn checked_div(self, rhs: Self) -> Option<Self> {
-            if unlikely!(rhs == 0 || (self == Self::MIN && rhs == -1)) {
+            // Using `&` helps LLVM see that it is the same check made in division.
+            if unlikely!(rhs == 0 || ((self == Self::MIN) & (rhs == -1))) {
                 None
             } else {
                 // SAFETY: div by zero and by INT_MIN have been checked above
@@ -569,7 +570,8 @@ macro_rules! int_impl {
                       without modifying the original"]
         #[inline]
         pub const fn checked_div_euclid(self, rhs: Self) -> Option<Self> {
-            if unlikely!(rhs == 0 || (self == Self::MIN && rhs == -1)) {
+            // Using `&` helps LLVM see that it is the same check made in division.
+            if unlikely!(rhs == 0 || ((self == Self::MIN) & (rhs == -1))) {
                 None
             } else {
                 Some(self.div_euclid(rhs))
@@ -595,7 +597,8 @@ macro_rules! int_impl {
                       without modifying the original"]
         #[inline]
         pub const fn checked_rem(self, rhs: Self) -> Option<Self> {
-            if unlikely!(rhs == 0 || (self == Self::MIN && rhs == -1)) {
+            // Using `&` helps LLVM see that it is the same check made in division.
+            if unlikely!(rhs == 0 || ((self == Self::MIN) & (rhs == -1))) {
                 None
             } else {
                 // SAFETY: div by zero and by INT_MIN have been checked above
@@ -621,7 +624,8 @@ macro_rules! int_impl {
                       without modifying the original"]
         #[inline]
         pub const fn checked_rem_euclid(self, rhs: Self) -> Option<Self> {
-            if unlikely!(rhs == 0 || (self == Self::MIN && rhs == -1)) {
+            // Using `&` helps LLVM see that it is the same check made in division.
+            if unlikely!(rhs == 0 || ((self == Self::MIN) & (rhs == -1))) {
                 None
             } else {
                 Some(self.rem_euclid(rhs))
@@ -1466,7 +1470,8 @@ macro_rules! int_impl {
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
         pub const fn overflowing_div(self, rhs: Self) -> (Self, bool) {
-            if unlikely!(self == Self::MIN && rhs == -1) {
+            // Using `&` helps LLVM see that it is the same check made in division.
+            if unlikely!((self == Self::MIN) & (rhs == -1)) {
                 (self, true)
             } else {
                 (self / rhs, false)
@@ -1496,7 +1501,8 @@ macro_rules! int_impl {
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
         pub const fn overflowing_div_euclid(self, rhs: Self) -> (Self, bool) {
-            if unlikely!(self == Self::MIN && rhs == -1) {
+            // Using `&` helps LLVM see that it is the same check made in division.
+            if unlikely!((self == Self::MIN) & (rhs == -1)) {
                 (self, true)
             } else {
                 (self.div_euclid(rhs), false)
@@ -1527,7 +1533,8 @@ macro_rules! int_impl {
         #[must_use = "this returns the result of the operation, \
                       without modifying the original"]
         pub const fn overflowing_rem(self, rhs: Self) -> (Self, bool) {
-            if unlikely!(self == Self::MIN && rhs == -1) {
+            // Using `&` helps LLVM see that it is the same check made in division.
+            if unlikely!((self == Self::MIN) & (rhs == -1)) {
                 (0, true)
             } else {
                 (self % rhs, false)
@@ -1558,7 +1565,8 @@ macro_rules! int_impl {
                       without modifying the original"]
         #[inline]
         pub const fn overflowing_rem_euclid(self, rhs: Self) -> (Self, bool) {
-            if unlikely!(self == Self::MIN && rhs == -1) {
+            // Using `&` helps LLVM see that it is the same check made in division.
+            if unlikely!((self == Self::MIN) & (rhs == -1)) {
                 (0, true)
             } else {
                 (self.rem_euclid(rhs), false)