Fix rare case where APInt divide algorithm applied un-needed transformation.

APInt uses Knuth's D algorithm for long division. In rare cases the
implementation applied a transformation that was not needed.

Added unit tests for long division. KnuthDiv() procedure is fully covered.
There is a case in APInt::divide() that I believe is never used (marked with
a comment) as all users of divide() handle trivial cases earlier.

Patch by Pawel Bylica!

  http://reviews.llvm.org/D8448

llvm-svn: 233312

1 files changed, 200 insertions, 0 deletions

diff --git a/llvm/unittests/ADT/APIntTest.cpp b/llvm/unittests/ADT/APIntTest.cpp
index 96fa0ddbeae..acdc1ecbbde 100644
--- a/llvm/unittests/ADT/APIntTest.cpp
+++ b/llvm/unittests/ADT/APIntTest.cpp
@@ -209,6 +209,206 @@ TEST(APIntTest, i1) {
   }
 }
 
+TEST(APIntTest, divrem_big1) {
+  // Tests KnuthDiv rare step D6
+  APInt a{256, "1ffffffffffffffff", 16};
+  APInt b{256, "1ffffffffffffffff", 16};
+  APInt c{256, 0};
+
+  auto p = a * b + c;
+  auto q = p.udiv(a);
+  auto r = p.urem(a);
+  EXPECT_EQ(q, b);
+  EXPECT_EQ(r, c);
+  APInt::udivrem(p, a, q, r);
+  EXPECT_EQ(q, b);
+  EXPECT_EQ(r, c);
+  q = p.udiv(b);
+  r = p.urem(b);
+  EXPECT_EQ(q, a);
+  EXPECT_EQ(r, c);
+  APInt::udivrem(p, b, q, r);
+  EXPECT_EQ(q, a);
+  EXPECT_EQ(r, c);
+  q = p.sdiv(a);
+  r = p.srem(a);
+  EXPECT_EQ(q, b);
+  EXPECT_EQ(r, c);
+  APInt::sdivrem(p, a, q, r);
+  EXPECT_EQ(q, b);
+  EXPECT_EQ(r, c);
+  q = p.sdiv(b);
+  r = p.srem(b);
+  EXPECT_EQ(q, a);
+  EXPECT_EQ(r, c);
+  APInt::sdivrem(p, b, q, r);
+  EXPECT_EQ(q, a);
+  EXPECT_EQ(r, c);
+}
+
+TEST(APIntTest, divrem_big2) {
+  // Tests KnuthDiv rare step D6
+  APInt a{1024,           "111111ffffffffffffffff"
+                "ffffffffffffffffffffffffffffffff"
+                "fffffffffffffffffffffffffffffccf"
+                "ffffffffffffffffffffffffffffff00", 16};
+  APInt b{1024,                       "112233ceff"
+                "cecece000000ffffffffffffffffffff"
+                "ffffffffffffffffffffffffffffffff"
+                "ffffffffffffffffffffffffffffffff"
+                "ffffffffffffffffffffffffffffff33", 16};
+  APInt c{1024, 7919};
+
+  auto p = a * b + c;
+  auto q = p.udiv(a);
+  auto r = p.urem(a);
+  EXPECT_EQ(q, b);
+  EXPECT_EQ(r, c);
+  APInt::udivrem(p, a, q, r);
+  EXPECT_EQ(q, b);
+  EXPECT_EQ(r, c);
+  q = p.udiv(b);
+  r = p.urem(b);
+  EXPECT_EQ(q, a);
+  EXPECT_EQ(r, c);
+  APInt::udivrem(p, b, q, r);
+  EXPECT_EQ(q, a);
+  EXPECT_EQ(r, c);
+  q = p.sdiv(a);
+  r = p.srem(a);
+  EXPECT_EQ(q, b);
+  EXPECT_EQ(r, c);
+  APInt::sdivrem(p, a, q, r);
+  EXPECT_EQ(q, b);
+  EXPECT_EQ(r, c);
+  q = p.sdiv(b);
+  r = p.srem(b);
+  EXPECT_EQ(q, a);
+  EXPECT_EQ(r, c);
+  APInt::sdivrem(p, b, q, r);
+  EXPECT_EQ(q, a);
+  EXPECT_EQ(r, c);
+}
+
+TEST(APIntTest, divrem_big3) {
+  // Tests KnuthDiv case without shift
+  APInt a{256, "ffffffffffffff0000000", 16};
+  APInt b{256, "80000001ffffffffffffffff", 16};
+  APInt c{256, 4219};
+
+  auto p = a * b + c;
+  auto q = p.udiv(a);
+  auto r = p.urem(a);
+  EXPECT_EQ(q, b);
+  EXPECT_EQ(r, c);
+  APInt::udivrem(p, a, q, r);
+  EXPECT_EQ(q, b);
+  EXPECT_EQ(r, c);
+  q = p.udiv(b);
+  r = p.urem(b);
+  EXPECT_EQ(q, a);
+  EXPECT_EQ(r, c);
+  APInt::udivrem(p, b, q, r);
+  EXPECT_EQ(q, a);
+  EXPECT_EQ(r, c);
+  q = p.sdiv(a);
+  r = p.srem(a);
+  EXPECT_EQ(q, b);
+  EXPECT_EQ(r, c);
+  APInt::sdivrem(p, a, q, r);
+  EXPECT_EQ(q, b);
+  EXPECT_EQ(r, c);
+  q = p.sdiv(b);
+  r = p.srem(b);
+  EXPECT_EQ(q, a);
+  EXPECT_EQ(r, c);
+  APInt::sdivrem(p, b, q, r);
+  EXPECT_EQ(q, a);
+  EXPECT_EQ(r, c);
+}
+
+TEST(APIntTest, divrem_big4) {
+  // Tests heap allocation in divide() enfoced by huge numbers
+  auto a = APInt{4096, 1}.shl(2000);
+  auto b = APInt{4096, 5}.shl(2001);
+  auto c = APInt{4096, 4219*13};
+
+  auto p = a * b + c;
+  auto q = p.udiv(a);
+  auto r = p.urem(a);
+  EXPECT_EQ(q, b);
+  EXPECT_EQ(r, c);
+  q = APInt{1024, 0}; // test non-single word APInt conversion in divide()
+  r = APInt{1024, 0};
+  APInt::udivrem(p, a, q, r);
+  EXPECT_EQ(q, b);
+  EXPECT_EQ(r, c);
+  q = p.udiv(b);
+  r = p.urem(b);
+  EXPECT_EQ(q, a);
+  EXPECT_EQ(r, c);
+  q = APInt{1024, 0};
+  r = APInt{1024, 0};
+  APInt::udivrem(p, b, q, r);
+  EXPECT_EQ(q, a);
+  EXPECT_EQ(r, c);
+  q = p.sdiv(a);
+  r = p.srem(a);
+  EXPECT_EQ(q, b);
+  EXPECT_EQ(r, c);
+  q = APInt{1024, 0};
+  r = APInt{1024, 0};
+  APInt::sdivrem(p, a, q, r);
+  EXPECT_EQ(q, b);
+  EXPECT_EQ(r, c);
+  q = p.sdiv(b);
+  r = p.srem(b);
+  EXPECT_EQ(q, a);
+  EXPECT_EQ(r, c);
+  q = APInt{1024, 0};
+  r = APInt{1024, 0};
+  APInt::sdivrem(p, b, q, r);
+  EXPECT_EQ(q, a);
+  EXPECT_EQ(r, c);
+}
+
+TEST(APIntTest, divrem_big5) {
+  // Tests one word divisor case of divide()
+  auto a = APInt{1024, 19}.shl(811);
+  auto b = APInt{1024, 4356013}; // one word
+  auto c = APInt{1024, 1};
+
+  auto p = a * b + c;
+  auto q = p.udiv(a);
+  auto r = p.urem(a);
+  EXPECT_EQ(q, b);
+  EXPECT_EQ(r, c);
+  APInt::udivrem(p, a, q, r);
+  EXPECT_EQ(q, b);
+  EXPECT_EQ(r, c);
+  q = p.udiv(b);
+  r = p.urem(b);
+  EXPECT_EQ(q, a);
+  EXPECT_EQ(r, c);
+  APInt::udivrem(p, b, q, r);
+  EXPECT_EQ(q, a);
+  EXPECT_EQ(r, c);
+  q = p.sdiv(a);
+  r = p.srem(a);
+  EXPECT_EQ(q, b);
+  EXPECT_EQ(r, c);
+  APInt::sdivrem(p, a, q, r);
+  EXPECT_EQ(q, b);
+  EXPECT_EQ(r, c);
+  q = p.sdiv(b);
+  r = p.srem(b);
+  EXPECT_EQ(q, a);
+  EXPECT_EQ(r, c);
+  APInt::sdivrem(p, b, q, r);
+  EXPECT_EQ(q, a);
+  EXPECT_EQ(r, c);
+}
+
 TEST(APIntTest, fromString) {
   EXPECT_EQ(APInt(32, 0), APInt(32,   "0", 2));
   EXPECT_EQ(APInt(32, 1), APInt(32,   "1", 2));