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[PM] Use a SmallVector instead of std::vector to avoid heap allocations

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for small switches, and avoid using a complex loop to set up the
weights.

We know what the baseline weights will be so we can just resize the
vector to contain all that value and clobber the one slot that is
likely. This seems much more direct than the previous code that tested
at every iteration, and started off by zeroing the vector.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@226995 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chandler Carruth 2015-01-24 10:47:13 +00:00
parent d491dadacd
commit fa50a1f2d5
1 changed files with 6 additions and 7 deletions
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13
lib/Transforms/Scalar/LowerExpectIntrinsic.cpp
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@ -12,6 +12,7 @@
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Constants.h"
@ -24,7 +25,6 @@
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include <vector>
using namespace llvm;
@ -73,13 +73,12 @@ static bool handleSwitchExpect(SwitchInst &SI) {
SwitchInst::CaseIt Case = SI.findCaseValue(ExpectedValue);
unsigned n = SI.getNumCases(); // +1 for default case.
std::vector<uint32_t> Weights(n + 1);
SmallVector<uint32_t, 16> Weights(n + 1, UnlikelyBranchWeight);
Weights[0] =
Case == SI.case_default() ? LikelyBranchWeight : UnlikelyBranchWeight;
for (unsigned i = 0; i != n; ++i)
Weights[i + 1] =
i == Case.getCaseIndex() ? LikelyBranchWeight : UnlikelyBranchWeight;
if (Case == SI.case_default())
Weights[0] = LikelyBranchWeight;
else
Weights[Case.getCaseIndex() + 1] = LikelyBranchWeight;
SI.setMetadata(LLVMContext::MD_prof,
MDBuilder(CI->getContext()).createBranchWeights(Weights));