From bc1430a0a0b3f97b86039950e57d832cb01f1cf6 Mon Sep 17 00:00:00 2001 From: Benjamin Kramer Date: Thu, 27 Oct 2011 16:38:50 +0000 Subject: [PATCH] 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 --- lib/Support/BlockFrequency.cpp | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/lib/Support/BlockFrequency.cpp b/lib/Support/BlockFrequency.cpp index a63bf83f203..84a993e3e5b 100644 --- a/lib/Support/BlockFrequency.cpp +++ b/lib/Support/BlockFrequency.cpp @@ -70,8 +70,13 @@ BlockFrequency &BlockFrequency::operator*=(const BranchProbability &Prob) { 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 @@ BlockFrequency &BlockFrequency::operator*=(const BranchProbability &Prob) { return *this; } - Frequency *= n; - Frequency /= d; + Frequency = mulRes / d; return *this; } -- 2.34.1