Bug fix in overflow detection on pow. With regression test.
Rationale:
Missed potential overflow in base update.
Test: test-art-host
Bug: 35706963
Change-Id: I117d96c1fa95dde37f5676f9dc750f0a71becafa
diff --git a/compiler/optimizing/induction_var_range.cc b/compiler/optimizing/induction_var_range.cc
index 1cd65c1..3dfe176 100644
--- a/compiler/optimizing/induction_var_range.cc
+++ b/compiler/optimizing/induction_var_range.cc
@@ -57,21 +57,27 @@
return false;
}
-/** Returns b^e for b,e >= 1. Sets overflow if arithmetic wrap-around occurred. */
+/** Computes a * b for a,b > 0 (at least until first overflow happens). */
+static int64_t SafeMul(int64_t a, int64_t b, /*out*/ bool* overflow) {
+ if (a > 0 && b > 0 && a > (std::numeric_limits<int64_t>::max() / b)) {
+ *overflow = true;
+ }
+ return a * b;
+}
+
+/** Returns b^e for b,e > 0. Sets overflow if arithmetic wrap-around occurred. */
static int64_t IntPow(int64_t b, int64_t e, /*out*/ bool* overflow) {
- DCHECK_GE(b, 1);
- DCHECK_GE(e, 1);
+ DCHECK_LT(0, b);
+ DCHECK_LT(0, e);
int64_t pow = 1;
while (e) {
if (e & 1) {
- int64_t oldpow = pow;
- pow *= b;
- if (pow < oldpow) {
- *overflow = true;
- }
+ pow = SafeMul(pow, b, overflow);
}
e >>= 1;
- b *= b;
+ if (e) {
+ b = SafeMul(b, b, overflow);
+ }
}
return pow;
}