maxjhandsome
/
llvm-project
forked from OSchip/llvm-project
1
0
Fork 0
Code Issues Pull Requests Packages Releases Wiki Activity

SimplifyCFG: preserve branch-weight metadata when creating a new switch from 

a pair of switch/branch where both depend on the value of the same variable and
the default case of the first switch/branch goes to the second switch/branch.

Code clean up and fixed a few issues:
1> handling the case where some cases of the 2nd switch are invalidated
2> correctly calculate the weight for the 2nd switch when it is a conditional eq

Testing case is modified from Alastair's original patch.

llvm-svn: 163635
This commit is contained in:
Manman Ren 2012-09-11 17:43:35 +00:00
parent 66d2e88799
commit 571d9e4b80
2 changed files with 137 additions and 81 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

126
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -752,38 +752,27 @@ static inline bool HasBranchWeights(const Instruction* I) {
return false;
}
/// Tries to get a branch weight for the given instruction, returns NULL if it
/// can't. Pos starts at 0.
static ConstantInt* GetWeight(Instruction* I, int Pos) {
MDNode* ProfMD = I->getMetadata(LLVMContext::MD_prof);
if (ProfMD && ProfMD->getOperand(0)) {
if (MDString* MDS = dyn_cast<MDString>(ProfMD->getOperand(0))) {
if (MDS->getString().equals("branch_weights")) {
assert(ProfMD->getNumOperands() >= 3);
return dyn_cast<ConstantInt>(ProfMD->getOperand(1 + Pos));
}
}
}
return 0;
}
/// Scale the given weights based on the successor TI's metadata. Scaling is
/// done by multiplying every weight by the sum of the successor's weights.
static void ScaleWeights(Instruction* STI, MutableArrayRef<uint64_t> Weights) {
// Sum the successor's weights
assert(HasBranchWeights(STI));
unsigned Scale = 0;
MDNode* ProfMD = STI->getMetadata(LLVMContext::MD_prof);
for (unsigned i = 1; i < ProfMD->getNumOperands(); ++i) {
ConstantInt* CI = dyn_cast<ConstantInt>(ProfMD->getOperand(i));
/// Get Weights of a given TerminatorInst, the default weight is at the front
/// of the vector. If TI is a conditional eq, we need to swap the branch-weight
/// metadata.
static void GetBranchWeights(TerminatorInst *TI,
SmallVectorImpl<uint64_t> &Weights) {
MDNode* MD = TI->getMetadata(LLVMContext::MD_prof);
assert(MD);
for (unsigned i = 1, e = MD->getNumOperands(); i < e; ++i) {
ConstantInt* CI = dyn_cast<ConstantInt>(MD->getOperand(i));
assert(CI);
Scale += CI->getValue().getZExtValue();
Weights.push_back(CI->getValue().getZExtValue());
}
// Skip default, as it's replaced during the folding
for (unsigned i = 1; i < Weights.size(); ++i) {
Weights[i] *= Scale;
// If TI is a conditional eq, the default case is the false case,
// and the corresponding branch-weight data is at index 2. We swap the
// default weight to be the first entry.
if (BranchInst* BI = dyn_cast<BranchInst>(TI)) {
assert(Weights.size() == 2);
ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
std::swap(Weights.front(), Weights.back());
}
}
@ -838,52 +827,22 @@ bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
// Update the branch weight metadata along the way
SmallVector<uint64_t, 8> Weights;
uint64_t PredDefaultWeight = 0;
bool PredHasWeights = HasBranchWeights(PTI);
bool SuccHasWeights = HasBranchWeights(TI);
if (PredHasWeights) {
MDNode* MD = PTI->getMetadata(LLVMContext::MD_prof);
assert(MD);
for (unsigned i = 1, e = MD->getNumOperands(); i < e; ++i) {
ConstantInt* CI = dyn_cast<ConstantInt>(MD->getOperand(i));
assert(CI);
Weights.push_back(CI->getValue().getZExtValue());
}
// If the predecessor is a conditional eq, then swap the default weight
// to be the first entry.
if (BranchInst* BI = dyn_cast<BranchInst>(PTI)) {
assert(Weights.size() == 2);
ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
if (ICI->getPredicate() == ICmpInst::ICMP_EQ) {
std::swap(Weights.front(), Weights.back());
}
}
PredDefaultWeight = Weights.front();
} else if (SuccHasWeights) {
if (PredHasWeights)
GetBranchWeights(PTI, Weights);
else if (SuccHasWeights)
// If there are no predecessor weights but there are successor weights,
// populate Weights with 1, which will later be scaled to the sum of
// successor's weights
Weights.assign(1 + PredCases.size(), 1);
PredDefaultWeight = 1;
}
uint64_t SuccDefaultWeight = 0;
if (SuccHasWeights) {
int Index = 0;
if (BranchInst* BI = dyn_cast<BranchInst>(TI)) {
ICmpInst* ICI = dyn_cast<ICmpInst>(BI->getCondition());
assert(ICI);
if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
Index = 1;
}
SuccDefaultWeight = GetWeight(TI, Index)->getValue().getZExtValue();
}
SmallVector<uint64_t, 8> SuccWeights;
if (SuccHasWeights)
GetBranchWeights(TI, SuccWeights);
else if (PredHasWeights)
SuccWeights.assign(1 + BBCases.size(), 1);
if (PredDefault == BB) {
// If this is the default destination from PTI, only the edges in TI
@ -896,7 +855,9 @@ bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
// The default destination is BB, we don't need explicit targets.
std::swap(PredCases[i], PredCases.back());
if (PredHasWeights) {
if (PredHasWeights || SuccHasWeights) {
// Increase weight for the default case.
Weights[0] += Weights[i+1];
std::swap(Weights[i+1], Weights.back());
Weights.pop_back();
}
@ -912,27 +873,30 @@ bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
NewSuccessors.push_back(BBDefault);
}
if (SuccHasWeights) {
ScaleWeights(TI, Weights);
Weights.front() *= SuccDefaultWeight;
} else if (PredHasWeights) {
Weights.front() /= (1 + BBCases.size());
}
unsigned CasesFromPred = Weights.size();
uint64_t ValidTotalSuccWeight = 0;
for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
if (!PTIHandled.count(BBCases[i].Value) &&
BBCases[i].Dest != BBDefault) {
PredCases.push_back(BBCases[i]);
NewSuccessors.push_back(BBCases[i].Dest);
if (SuccHasWeights) {
Weights.push_back(PredDefaultWeight *
GetWeight(TI, i)->getValue().getZExtValue());
} else if (PredHasWeights) {
// Split the old default's weight amongst the children
Weights.push_back(PredDefaultWeight / (1 + BBCases.size()));
if (SuccHasWeights || PredHasWeights) {
// The default weight is at index 0, so weight for the ith case
// should be at index i+1. Scale the cases from successor by
// PredDefaultWeight (Weights[0]).
Weights.push_back(Weights[0] * SuccWeights[i+1]);
ValidTotalSuccWeight += SuccWeights[i+1];
}
}
if (SuccHasWeights || PredHasWeights) {
ValidTotalSuccWeight += SuccWeights[0];
// Scale the cases from predecessor by ValidTotalSuccWeight.
for (unsigned i = 1; i < CasesFromPred; ++i)
Weights[i] *= ValidTotalSuccWeight;
// Scale the default weight by SuccDefaultWeight (SuccWeights[0]).
Weights[0] *= SuccWeights[0];
}
} else {
// FIXME: preserve branch weight metadata, similarly to the 'then'
// above. For now, drop it.

92
llvm/test/Transforms/SimplifyCFG/preserve-branchweights-switch-create.ll Normal file
View File

@ -0,0 +1,92 @@
; RUN: opt -simplifycfg -S -o - < %s | FileCheck %s
declare void @func2(i32)
declare void @func4(i32)
declare void @func6(i32)
declare void @func8(i32)
;; test1 - create a switch with case 2 and case 4 from two branches: N == 2
;; and N == 4.
define void @test1(i32 %N) nounwind uwtable {
entry:
%cmp = icmp eq i32 %N, 2
br i1 %cmp, label %if.then, label %if.else, !prof !0
; CHECK: test1
; CHECK: switch i32 %N
; CHECK: ], !prof !0
if.then:
call void @func2(i32 %N) nounwind
br label %if.end9
if.else:
%cmp2 = icmp eq i32 %N, 4
br i1 %cmp2, label %if.then7, label %if.else8, !prof !1
if.then7:
call void @func4(i32 %N) nounwind
br label %if.end
if.else8:
call void @func8(i32 %N) nounwind
br label %if.end
if.end:
br label %if.end9
if.end9:
ret void
}
;; test2 - Merge two switches where PredDefault == BB.
define void @test2(i32 %M, i32 %N) nounwind uwtable {
entry:
%cmp = icmp sgt i32 %M, 2
br i1 %cmp, label %sw1, label %sw2
sw1:
switch i32 %N, label %sw2 [
i32 2, label %sw.bb
i32 3, label %sw.bb1
], !prof !2
; CHECK: test2
; CHECK: switch i32 %N, label %sw.epilog
; CHECK: i32 2, label %sw.bb
; CHECK: i32 3, label %sw.bb1
; CHECK: i32 4, label %sw.bb5
; CHECK: ], !prof !1
sw.bb:
call void @func2(i32 %N) nounwind
br label %sw.epilog
sw.bb1:
call void @func4(i32 %N) nounwind
br label %sw.epilog
sw2:
;; Here "case 2" is invalidated if control is transferred through default case
;; of the first switch.
switch i32 %N, label %sw.epilog [
i32 2, label %sw.bb4
i32 4, label %sw.bb5
], !prof !3
sw.bb4:
call void @func6(i32 %N) nounwind
br label %sw.epilog
sw.bb5:
call void @func8(i32 %N) nounwind
br label %sw.epilog
sw.epilog:
ret void
}
!0 = metadata !{metadata !"branch_weights", i32 64, i32 4}
!1 = metadata !{metadata !"branch_weights", i32 4, i32 64}
; CHECK: !0 = metadata !{metadata !"branch_weights", i32 256, i32 4352, i32 16}
!2 = metadata !{metadata !"branch_weights", i32 4, i32 4, i32 8}
!3 = metadata !{metadata !"branch_weights", i32 8, i32 8, i32 4}
; CHECK: !1 = metadata !{metadata !"branch_weights", i32 32, i32 48, i32 96, i32 16}