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;
}
diff --git a/test/623-checker-loop-regressions/src/Main.java b/test/623-checker-loop-regressions/src/Main.java
index 7509d9b..2a7be2f 100644
--- a/test/623-checker-loop-regressions/src/Main.java
+++ b/test/623-checker-loop-regressions/src/Main.java
@@ -213,6 +213,8 @@
/// CHECK-START: long Main.geoLongDivLastValue(long) instruction_simplifier$after_bce (after)
/// CHECK-DAG: <<Long:j\d+>> LongConstant 0 loop:none
/// CHECK-DAG: Return [<<Long>>] loop:none
+ //
+ // Tests overflow in the divisor (while updating intermediate result).
static long geoLongDivLastValue(long x) {
for (int i = 0; i < 10; i++) {
x /= 1081788608;
@@ -220,6 +222,26 @@
return x;
}
+ /// CHECK-START: long Main.geoLongDivLastValue() loop_optimization (before)
+ /// CHECK-DAG: Phi loop:<<Loop:B\d+>> outer_loop:none
+ /// CHECK-DAG: Phi loop:<<Loop>> outer_loop:none
+ //
+ /// CHECK-START: long Main.geoLongDivLastValue() loop_optimization (after)
+ /// CHECK-NOT: Phi
+ //
+ /// CHECK-START: long Main.geoLongDivLastValue() instruction_simplifier$after_bce (after)
+ /// CHECK-DAG: <<Long:j\d+>> LongConstant 0 loop:none
+ /// CHECK-DAG: Return [<<Long>>] loop:none
+ //
+ // Tests overflow in the divisor (while updating base).
+ static long geoLongDivLastValue() {
+ long x = -1;
+ for (int i2 = 0; i2 < 2; i2++) {
+ x /= (Long.MAX_VALUE);
+ }
+ return x;
+ }
+
/// CHECK-START: long Main.geoLongMulLastValue(long) loop_optimization (before)
/// CHECK-DAG: Phi loop:<<Loop:B\d+>> outer_loop:none
/// CHECK-DAG: Phi loop:<<Loop>> outer_loop:none
@@ -286,6 +308,8 @@
expectEquals(0L, geoLongDivLastValue(9223372036854775807L));
expectEquals(0L, geoLongDivLastValue(-9223372036854775808L));
+ expectEquals(0L, geoLongDivLastValue());
+
expectEquals( 0L, geoLongMulLastValue(0L));
expectEquals(-8070450532247928832L, geoLongMulLastValue(1L));
expectEquals( 2305843009213693952L, geoLongMulLastValue(2L));