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author | Hal Finkel <hfinkel@anl.gov> | 2013-11-01 10:58:22 +0000 |
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committer | Hal Finkel <hfinkel@anl.gov> | 2013-11-01 10:58:22 +0000 |
commit | e14fb073574dcb74de05bdeedbfb3fcffbfa1bf6 (patch) | |
tree | 10a5655b64112d33790b371fde46bb0be6693316 /lib/Analysis | |
parent | 0097e155025767c11790912dcf780f82dffaffb1 (diff) | |
download | llvm-e14fb073574dcb74de05bdeedbfb3fcffbfa1bf6.tar.gz llvm-e14fb073574dcb74de05bdeedbfb3fcffbfa1bf6.tar.bz2 llvm-e14fb073574dcb74de05bdeedbfb3fcffbfa1bf6.tar.xz |
Consider (x == -1) unlikely in BranchProbabilityInfo
This adds another heuristic to BPI, similar to the existing heuristic that
considers (x == 0) unlikely to be true. As suggested in the PACT'98 paper by
Deitrich, Cheng, and Hwu, -1 is often used to indicate an invalid index, and
equality comparisons with -1 are also unlikely to succeed. Local
experimentation supports this hypothesis: This yields a 1-2% speedup in the
test-suite sqlite benchmark on the PPC A2 core, with no significant
regressions.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193855 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/Analysis')
-rw-r--r-- | lib/Analysis/BranchProbabilityInfo.cpp | 22 |
1 files changed, 18 insertions, 4 deletions
diff --git a/lib/Analysis/BranchProbabilityInfo.cpp b/lib/Analysis/BranchProbabilityInfo.cpp index 7cdf828c2f..86560ca33d 100644 --- a/lib/Analysis/BranchProbabilityInfo.cpp +++ b/lib/Analysis/BranchProbabilityInfo.cpp @@ -398,10 +398,24 @@ bool BranchProbabilityInfo::calcZeroHeuristics(BasicBlock *BB) { // InstCombine canonicalizes X <= 0 into X < 1. // X <= 0 -> Unlikely isProb = false; - } else if (CV->isAllOnesValue() && CI->getPredicate() == CmpInst::ICMP_SGT) { - // InstCombine canonicalizes X >= 0 into X > -1. - // X >= 0 -> Likely - isProb = true; + } else if (CV->isAllOnesValue()) { + switch (CI->getPredicate()) { + case CmpInst::ICMP_EQ: + // X == -1 -> Unlikely + isProb = false; + break; + case CmpInst::ICMP_NE: + // X != -1 -> Likely + isProb = true; + break; + case CmpInst::ICMP_SGT: + // InstCombine canonicalizes X >= 0 into X > -1. + // X >= 0 -> Likely + isProb = true; + break; + default: + return false; + } } else { return false; } |