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| author | Benjamin Kramer <benny.kra@googlemail.com> | 2011-10-27 16:38:50 +0000 |
|---|---|---|
| committer | Stephen Hines <srhines@google.com> | 2011-11-14 09:11:21 -0800 |
| commit | 09890f41b6ace75ee6a177de18b9fc1e6100d696 (patch) | |
| tree | 0f3dabaf5b02ea36d4bf55f609923297f47fe320 /lib/Support | |
| parent | 25fffee3077e41a82587c086fe22c4bdc783d659 (diff) | |
| download | external_llvm-09890f41b6ace75ee6a177de18b9fc1e6100d696.zip external_llvm-09890f41b6ace75ee6a177de18b9fc1e6100d696.tar.gz external_llvm-09890f41b6ace75ee6a177de18b9fc1e6100d696.tar.bz2 | |
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
Diffstat (limited to 'lib/Support')
| -rw-r--r-- | lib/Support/BlockFrequency.cpp | 12 |
1 files changed, 8 insertions, 4 deletions
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 @@ 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; } |