Fix a bad overflow check pointed out by Ben.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185226 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Support/BlockFrequency.cpp

@@ -47,9 +47,7 @@ static uint64_t div96bit(uint64_t W[2], uint32_t D) {
   uint64_t x = W[1];
   unsigned i;
 
-  // This is really a 64-bit division.
-  if (!x)
-    return y / D;
+  assert(x != 0 && "This is really a 64-bit division");
 
   // This long division algorithm automatically saturates on overflow.
   for (i = 0; i < 64 && x; ++i) {
@@ -75,7 +73,7 @@ void BlockFrequency::scale(uint32_t N, uint32_t D) {
   uint64_t MulRes = (MulHi << 32) + MulLo;
 
   // If the product fits in 64 bits, just use built-in division.
-  if (MulHi <= UINT32_MAX && MulRes <= MulLo) {
+  if (MulHi <= UINT32_MAX && MulRes >= MulLo) {
     Frequency = MulRes / D;
     return;
   }

unittests/Support/BlockFrequencyTest.cpp

@@ -68,6 +68,11 @@ TEST(BlockFrequencyTest, Saturate) {
   Freq = 0x1000000000000000ULL;
   Freq /= BranchProbability(10000, 160000);
   EXPECT_EQ(Freq.getFrequency(), UINT64_MAX);
+
+  // Try to cheat the multiplication overflow check.
+  Freq = 0x00000001f0000001ull;
+  Freq /= BranchProbability(1000, 0xf000000f);
+  EXPECT_EQ(33506781356485509ULL, Freq.getFrequency());
 }
 
 TEST(BlockFrequencyTest, ProbabilityCompare) {