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Generalize the reading of probability metadata to work for both branches

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and switches, with arbitrary numbers of successors. Still optimized for
the common case of 2 successors for a conditional branch.

Add a test case for switch metadata showing up in the BlockFrequencyInfo pass.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@142493 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chandler Carruth 2011-10-19 10:32:19 +00:00
parent 99d01c54a0
commit 941aa7b1e8
2 changed files with 67 additions and 16 deletions
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40
lib/Analysis/BranchProbabilityInfo.cpp
View File

@ -140,30 +140,38 @@ public:
// Propagate existing explicit probabilities from either profile data or
// 'expect' intrinsic processing.
// FIXME: This doesn't correctly extract probabilities for switches.
bool BranchProbabilityAnalysis::calcMetadataWeights(BasicBlock *BB) {
BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator());
if (!BI || !BI->isConditional())
TerminatorInst *TI = BB->getTerminator();
if (TI->getNumSuccessors() == 1)
return false;
if (!isa<BranchInst>(TI) && !isa<SwitchInst>(TI))
return false;
MDNode *WeightsNode = BI->getMetadata(LLVMContext::MD_prof);
if (!WeightsNode || WeightsNode->getNumOperands() < 3)
MDNode *WeightsNode = TI->getMetadata(LLVMContext::MD_prof);
if (!WeightsNode)
return false;
// Pull the weights out of the metadata. Note that the zero operand is the
// name.
ConstantInt *Weights[] = {
dyn_cast<ConstantInt>(WeightsNode->getOperand(1)),
dyn_cast<ConstantInt>(WeightsNode->getOperand(2))
};
if (!Weights[0] || !Weights[1])
// Ensure there are weights for all of the successors. Note that the first
// operand to the metadata node is a name, not a weight.
if (WeightsNode->getNumOperands() != TI->getNumSuccessors() + 1)
return false;
// Build up the final weights that will be used in a temporary buffer, but
// don't add them until all weihts are present. Each weight value is clamped
// to [1, getMaxWeightFor(BB)].
uint32_t WeightLimit = getMaxWeightFor(BB);
BP->setEdgeWeight(BB, BI->getSuccessor(0),
Weights[0]->getLimitedValue(WeightLimit));
BP->setEdgeWeight(BB, BI->getSuccessor(1),
Weights[1]->getLimitedValue(WeightLimit));
SmallVector<uint32_t, 2> Weights;
Weights.reserve(TI->getNumSuccessors());
for (unsigned i = 1, e = WeightsNode->getNumOperands(); i != e; ++i) {
ConstantInt *Weight = dyn_cast<ConstantInt>(WeightsNode->getOperand(i));
if (!Weight)
return false;
Weights.push_back(
std::max<uint32_t>(1, Weight->getLimitedValue(WeightLimit)));
}
assert(Weights.size() == TI->getNumSuccessors() && "Checked above");
for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
BP->setEdgeWeight(BB, TI->getSuccessor(i), Weights[i]);
return true;
}

43
test/Analysis/BlockFrequencyInfo/basic.ll
View File

@ -47,3 +47,46 @@ exit:
}
!0 = metadata !{metadata !"branch_weights", i32 64, i32 4}
define i32 @test3(i32 %i, i32 %a, i32 %b, i32 %c, i32 %d, i32 %e) {
; CHECK: Printing analysis {{.*}} for function 'test3'
; CHECK: entry = 1024
entry:
switch i32 %i, label %case_a [ i32 1, label %case_b
i32 2, label %case_c
i32 3, label %case_d
i32 4, label %case_e ], !prof !1
; CHECK: case_a = 51
case_a:
br label %exit
; CHECK: case_b = 51
case_b:
br label %exit
; The 'case_c' branch is predicted more likely via branch weight metadata.
; CHECK: case_c = 819
case_c:
br label %exit
; CHECK: case_d = 51
case_d:
br label %exit
; CHECK: case_e = 51
case_e:
br label %exit
; FIXME: It may be a bug that we don't sum back to 1024.
; CHECK: exit = 1023
exit:
%result = phi i32 [ %a, %case_a ],
[ %b, %case_b ],
[ %c, %case_c ],
[ %d, %case_d ],
[ %e, %case_e ]
ret i32 %result
}
!1 = metadata !{metadata !"branch_weights", i32 4, i32 4, i32 64, i32 4, i32 4}