BlockFrequency: Use a smarter overflow check.
This trades one 64 bit div for one 64 bit mul and some arithmetic.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@143106 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Support/BlockFrequency.cpp b/lib/Support/BlockFrequency.cpp
index a63bf83..84a993e 100644
--- a/lib/Support/BlockFrequency.cpp
+++ b/lib/Support/BlockFrequency.cpp
@@ -70,8 +70,13 @@
assert(n <= d && "Probability must be less or equal to 1.");
- // If we can overflow use 96-bit operations.
- if (n > 0 && Frequency > UINT64_MAX / n) {
+ // Calculate Frequency * n.
+ uint64_t mulLo = (Frequency & UINT32_MAX) * n;
+ uint64_t mulHi = (Frequency >> 32) * n;
+ uint64_t mulRes = (mulHi << 32) + mulLo;
+
+ // If there was overflow use 96-bit operations.
+ if (mulHi > UINT32_MAX || mulRes < mulLo) {
// 96-bit value represented as W[1]:W[0].
uint64_t W[2];
@@ -82,8 +87,7 @@
return *this;
}
- Frequency *= n;
- Frequency /= d;
+ Frequency = mulRes / d;
return *this;
}