commit b603a5cdff7c1fb300b83175bfb3cd990fdd6265
author Aart Bik <ajcbik@google.com> Mon Mar 06 18:29:39 2017 -0800
committer Aart Bik <ajcbik@google.com> Tue Mar 07 08:59:08 2017 -0800
tree 523f82d02727bd095c650463e0087af3853f59df
parent d88663823f75dbd68cace178ddca4767775d97a1

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

compiler/optimizing/induction_var_range.cc

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;
 }

test/623-checker-loop-regressions/src/Main.java

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));