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PGO: preserve branch-weight metadata when simplifying a switch with a single

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case to a conditional branch and when removing dead cases.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@163942 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Manman Ren 2012-09-14 21:53:06 +00:00
parent 911908dcb8
commit ad2890760f
3 changed files with 82 additions and 3 deletions
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16
lib/Transforms/Utils/Local.cpp
View File

@ -200,8 +200,20 @@ bool llvm::ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions,
"cond");
// Insert the new branch.
Builder.CreateCondBr(Cond, FirstCase.getCaseSuccessor(),
SI->getDefaultDest());
BranchInst *NewBr = Builder.CreateCondBr(Cond,
FirstCase.getCaseSuccessor(),
SI->getDefaultDest());
MDNode* MD = SI->getMetadata(LLVMContext::MD_prof);
if (MD && MD->getNumOperands() == 3) {
ConstantInt *SICase = dyn_cast<ConstantInt>(MD->getOperand(2));
ConstantInt *SIDef = dyn_cast<ConstantInt>(MD->getOperand(1));
assert(SICase && SIDef);
// The TrueWeight should be the weight for the single case of SI.
NewBr->setMetadata(LLVMContext::MD_prof,
MDBuilder(BB->getContext()).
createBranchWeights(SICase->getValue().getZExtValue(),
SIDef->getValue().getZExtValue()));
}
// Delete the old switch.
SI->eraseFromParent();

19
lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -667,13 +667,32 @@ SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
<< "Through successor TI: " << *TI);
// Collect branch weights into a vector.
SmallVector<uint32_t, 8> Weights;
MDNode* MD = SI->getMetadata(LLVMContext::MD_prof);
bool HasWeight = MD && (MD->getNumOperands() == 2 + SI->getNumCases());
if (HasWeight)
for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e;
++MD_i) {
ConstantInt* CI = dyn_cast<ConstantInt>(MD->getOperand(MD_i));
assert(CI);
Weights.push_back(CI->getValue().getZExtValue());
}
for (SwitchInst::CaseIt i = SI->case_end(), e = SI->case_begin(); i != e;) {
--i;
if (DeadCases.count(i.getCaseValue())) {
if (HasWeight) {
std::swap(Weights[i.getCaseIndex()+1], Weights.back());
Weights.pop_back();
}
i.getCaseSuccessor()->removePredecessor(TI->getParent());
SI->removeCase(i);
}
}
if (HasWeight)
SI->setMetadata(LLVMContext::MD_prof,
MDBuilder(SI->getParent()->getContext()).
createBranchWeights(Weights));
DEBUG(dbgs() << "Leaving: " << *TI << "\n");
return true;

50
test/Transforms/SimplifyCFG/preserve-branchweights.ll
View File

@ -109,12 +109,60 @@ sw.epilog:
ret void
}
;; test6 - Some cases of the second switch are pruned during optimization.
;; Then the second switch will be converted to a branch, finally, the first
;; switch and the branch will be merged into a single switch.
define void @test6(i32 %M, i32 %N) nounwind uwtable {
entry:
switch i32 %N, label %sw2 [
i32 1, label %sw2
i32 2, label %sw.bb
i32 3, label %sw.bb1
], !prof !4
; CHECK: test6
; CHECK: switch i32 %N, label %sw.epilog
; CHECK: i32 3, label %sw.bb1
; CHECK: i32 2, label %sw.bb
; CHECK: i32 4, label %sw.bb5
; CHECK: ], !prof !3
sw.bb:
call void @helper(i32 0)
br label %sw.epilog
sw.bb1:
call void @helper(i32 1)
br label %sw.epilog
sw2:
;; Here "case 2" is invalidated since the default case of the first switch
;; does not include "case 2".
switch i32 %N, label %sw.epilog [
i32 2, label %sw.bb4
i32 4, label %sw.bb5
], !prof !5
sw.bb4:
call void @helper(i32 2)
br label %sw.epilog
sw.bb5:
call void @helper(i32 3)
br label %sw.epilog
sw.epilog:
ret void
}
!0 = metadata !{metadata !"branch_weights", i32 3, i32 5}
!1 = metadata !{metadata !"branch_weights", i32 1, i32 1}
!2 = metadata !{metadata !"branch_weights", i32 1, i32 2}
!3 = metadata !{metadata !"branch_weights", i32 4, i32 3, i32 2, i32 1}
!4 = metadata !{metadata !"branch_weights", i32 4, i32 3, i32 2, i32 1}
!5 = metadata !{metadata !"branch_weights", i32 7, i32 6, i32 5}
; CHECK: !0 = metadata !{metadata !"branch_weights", i32 5, i32 11}
; CHECK: !1 = metadata !{metadata !"branch_weights", i32 1, i32 5}
; CHECK: !2 = metadata !{metadata !"branch_weights", i32 7, i32 1, i32 2}
; CHECK-NOT: !3
; CHECK: !3 = metadata !{metadata !"branch_weights", i32 49, i32 12, i32 24, i32 35}
; CHECK-NOT: !4