[llvm-commits] [llvm] r163635 - in /llvm/trunk: lib/Transforms/Utils/SimplifyCFG.cpp test/Transforms/SimplifyCFG/preserve-branchweights-switch-create.ll
Manman Ren
mren at apple.com
Tue Sep 11 10:43:35 PDT 2012
Author: mren
Date: Tue Sep 11 12:43:35 2012
New Revision: 163635
URL: http://llvm.org/viewvc/llvm-project?rev=163635&view=rev
Log:
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.
Added:
llvm/trunk/test/Transforms/SimplifyCFG/preserve-branchweights-switch-create.ll
Modified:
llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
Modified: llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp?rev=163635&r1=163634&r2=163635&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp Tue Sep 11 12:43:35 2012
@@ -752,38 +752,27 @@
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 @@
// 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 @@
// 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 @@
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.
Added: llvm/trunk/test/Transforms/SimplifyCFG/preserve-branchweights-switch-create.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SimplifyCFG/preserve-branchweights-switch-create.ll?rev=163635&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/SimplifyCFG/preserve-branchweights-switch-create.ll (added)
+++ llvm/trunk/test/Transforms/SimplifyCFG/preserve-branchweights-switch-create.ll Tue Sep 11 12:43:35 2012
@@ -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}
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