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Correct overflow check; signed integer overflow is undefined in C++.

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BUG=
R=fschneider@google.com

Review URL: https://codereview.chromium.org/1490853002 .
This commit is contained in:
Srdjan Mitrovic
2015-12-02 08:45:41 -08:00
parent 1328c98cc2
commit abef5cb3ed
1 changed files with 2 additions and 13 deletions
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runtime/vm/object.cc
+2 -13
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@@ -17293,24 +17293,13 @@ RawInteger* Integer::ArithmeticOp(Token::Kind operation,
const int64_t right_value = other.AsInt64Value();
switch (operation) {
case Token::kADD: {
if (((left_value < 0) != (right_value < 0)) ||
((left_value + right_value) < 0) == (left_value < 0)) {
if (!Utils::WillAddOverflow(left_value, right_value)) {
return Integer::New(left_value + right_value, space);
}
break;
}
case Token::kSUB: {
// TODO(srdjan): XCode 7 produces different code in -O0 than in -O2 for
// following code when 'left_value - right_value' overflows into a
// positive number (left negative, right positive):
// if (((left_value < 0) == (right_value < 0)) ||
// ((left_value - right_value) < 0) == (left_value < 0)) {
//
// Restructuring code using temporary variables is a workaround.
const bool both_same_sign = (left_value < 0) == (right_value < 0);
const bool result_same_sign_as_left =
((left_value - right_value) < 0) == (left_value < 0);
if (both_same_sign || result_same_sign_as_left) {
if (!Utils::WillSubOverflow(left_value, right_value)) {
return Integer::New(left_value - right_value, space);
}
break;