[llvm] r311727 - [Profile] backward propagate profile info in JumpThreading
Xinliang David Li via llvm-commits
llvm-commits at lists.llvm.org
Thu Aug 24 15:54:02 PDT 2017
Author: davidxl
Date: Thu Aug 24 15:54:01 2017
New Revision: 311727
URL: http://llvm.org/viewvc/llvm-project?rev=311727&view=rev
Log:
[Profile] backward propagate profile info in JumpThreading
Take-2 after fixing bugs in the original patch.
Differential Revsion: http://reviews.llvm.org/D36864
Added:
llvm/trunk/test/Transforms/JumpThreading/threading_prof1.ll
llvm/trunk/test/Transforms/JumpThreading/threading_prof2.ll
Modified:
llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp
Modified: llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp?rev=311727&r1=311726&r2=311727&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/JumpThreading.cpp Thu Aug 24 15:54:01 2017
@@ -126,7 +126,116 @@ JumpThreadingPass::JumpThreadingPass(int
BBDupThreshold = (T == -1) ? BBDuplicateThreshold : unsigned(T);
}
-/// runOnFunction - Top level algorithm.
+// Update branch probability information according to conditional
+// branch probablity. This is usually made possible for cloned branches
+// in inline instances by the context specific profile in the caller.
+// For instance,
+//
+// [Block PredBB]
+// [Branch PredBr]
+// if (t) {
+// Block A;
+// } else {
+// Block B;
+// }
+//
+// [Block BB]
+// cond = PN([true, %A], [..., %B]); // PHI node
+// [Branch CondBr]
+// if (cond) {
+// ... // P(cond == true) = 1%
+// }
+//
+// Here we know that when block A is taken, cond must be true, which means
+// P(cond == true | A) = 1
+//
+// Given that P(cond == true) = P(cond == true | A) * P(A) +
+// P(cond == true | B) * P(B)
+// we get
+// P(cond == true ) = P(A) + P(cond == true | B) * P(B)
+//
+// which gives us:
+// P(A) <= P(c == true), i.e.
+// P(t == true) <= P(cond == true)
+//
+// In other words, if we know P(cond == true), we know that P(t == true)
+// can not be greater than 1%.
+static void updatePredecessorProfileMetadata(PHINode *PN, BasicBlock *BB) {
+ BranchInst *CondBr = dyn_cast<BranchInst>(BB->getTerminator());
+ if (!CondBr)
+ return;
+
+ BranchProbability BP;
+ uint64_t TrueWeight, FalseWeight;
+ if (!CondBr->extractProfMetadata(TrueWeight, FalseWeight))
+ return;
+
+ // Returns the outgoing edge of the dominating predecessor block
+ // that leads to the PhiNode's incoming block:
+ auto GetPredOutEdge =
+ [](BasicBlock *IncomingBB,
+ BasicBlock *PhiBB) -> std::pair<BasicBlock *, BasicBlock *> {
+ auto *PredBB = IncomingBB;
+ auto *SuccBB = PhiBB;
+ for (;;) {
+ BranchInst *PredBr = dyn_cast<BranchInst>(PredBB->getTerminator());
+ if (PredBr && PredBr->isConditional())
+ return {PredBB, SuccBB};
+ auto *SinglePredBB = PredBB->getSinglePredecessor();
+ if (!SinglePredBB)
+ return {nullptr, nullptr};
+ SuccBB = PredBB;
+ PredBB = SinglePredBB;
+ }
+ };
+
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
+ Value *PhiOpnd = PN->getIncomingValue(i);
+ ConstantInt *CI = dyn_cast<ConstantInt>(PhiOpnd);
+
+ if (!CI || !CI->getType()->isIntegerTy(1))
+ continue;
+
+ BP = (CI->isOne() ? BranchProbability::getBranchProbability(
+ TrueWeight, TrueWeight + FalseWeight)
+ : BranchProbability::getBranchProbability(
+ FalseWeight, TrueWeight + FalseWeight));
+
+ auto PredOutEdge = GetPredOutEdge(PN->getIncomingBlock(i), BB);
+ if (!PredOutEdge.first)
+ return;
+
+ BasicBlock *PredBB = PredOutEdge.first;
+ BranchInst *PredBr = cast<BranchInst>(PredBB->getTerminator());
+
+ uint64_t PredTrueWeight, PredFalseWeight;
+ // FIXME: We currently only set the profile data when it is missing.
+ // With PGO, this can be used to refine even existing profile data with
+ // context information. This needs to be done after more performance
+ // testing.
+ if (PredBr->extractProfMetadata(PredTrueWeight, PredFalseWeight))
+ continue;
+
+ // We can not infer anything useful when BP >= 50%, because BP is the
+ // upper bound probability value.
+ if (BP >= BranchProbability(50, 100))
+ continue;
+
+ SmallVector<uint32_t, 2> Weights;
+ if (PredBr->getSuccessor(0) == PredOutEdge.second) {
+ Weights.push_back(BP.getNumerator());
+ Weights.push_back(BP.getCompl().getNumerator());
+ } else {
+ Weights.push_back(BP.getCompl().getNumerator());
+ Weights.push_back(BP.getNumerator());
+ }
+ PredBr->setMetadata(LLVMContext::MD_prof,
+ MDBuilder(PredBr->getParent()->getContext())
+ .createBranchWeights(Weights));
+ }
+}
+
+/// runOnFunction - Toplevel algorithm.
///
bool JumpThreading::runOnFunction(Function &F) {
if (skipFunction(F))
@@ -991,6 +1100,11 @@ bool JumpThreadingPass::ProcessBlock(Bas
if (SimplifyPartiallyRedundantLoad(LI))
return true;
+ // Before threading, try to propagate profile data backwards:
+ if (PHINode *PN = dyn_cast<PHINode>(CondInst))
+ if (PN->getParent() == BB && isa<BranchInst>(BB->getTerminator()))
+ updatePredecessorProfileMetadata(PN, BB);
+
// Handle a variety of cases where we are branching on something derived from
// a PHI node in the current block. If we can prove that any predecessors
// compute a predictable value based on a PHI node, thread those predecessors.
Added: llvm/trunk/test/Transforms/JumpThreading/threading_prof1.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/JumpThreading/threading_prof1.ll?rev=311727&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/JumpThreading/threading_prof1.ll (added)
+++ llvm/trunk/test/Transforms/JumpThreading/threading_prof1.ll Thu Aug 24 15:54:01 2017
@@ -0,0 +1,99 @@
+; RUN: opt -jump-threading -S < %s | FileCheck %s
+; RUN: opt -passes=jump-threading -S < %s | FileCheck %s
+
+define void @test() {
+; CHECK-LABEL: @test()
+bb:
+ %tmp = call i32 @a()
+ %tmp1 = icmp eq i32 %tmp, 1
+ br i1 %tmp1, label %bb5, label %bb2
+; CHECK: br i1 %tmp1,{{.*}} !prof ![[PROF1:[0-9]+]]
+
+bb2: ; preds = %bb
+ %tmp3 = call i32 @b()
+ %tmp4 = icmp ne i32 %tmp3, 1
+ br label %bb5
+; CHECK: br i1 %tmp4, {{.*}} !prof ![[PROF2:[0-9]+]]
+
+bb5: ; preds = %bb2, %bb
+ %tmp6 = phi i1 [ false, %bb ], [ %tmp4, %bb2 ]
+ br i1 %tmp6, label %bb8, label %bb7, !prof !0
+
+bb7: ; preds = %bb5
+ call void @bar()
+ br label %bb8
+
+bb8: ; preds = %bb7, %bb5
+ ret void
+}
+
+define void @test_single_pred1() {
+; CHECK-LABEL: @test_single_pred1()
+bb:
+ %tmp = call i32 @a()
+ %tmp1 = icmp eq i32 %tmp, 1
+ br i1 %tmp1, label %bb5_1, label %bb2
+; CHECK: br i1 %tmp1,{{.*}} !prof ![[PROF1:[0-9]+]]
+
+bb5_1:
+ br label %bb5;
+
+bb2:
+ %tmp3 = call i32 @b()
+ %tmp4 = icmp ne i32 %tmp3, 1
+ br label %bb5
+; CHECK: br i1 %tmp4, {{.*}} !prof ![[PROF2:[0-9]+]]
+
+bb5:
+ %tmp6 = phi i1 [ false, %bb5_1 ], [ %tmp4, %bb2 ]
+ br i1 %tmp6, label %bb8, label %bb7, !prof !0
+
+bb7:
+ call void @bar()
+ br label %bb8
+
+bb8:
+ ret void
+}
+
+define void @test_single_pred2() {
+; CHECK-LABEL: @test_single_pred2()
+bb:
+ %tmp = call i32 @a()
+ %tmp1 = icmp eq i32 %tmp, 1
+ br i1 %tmp1, label %bb5_1, label %bb2
+; CHECK: br i1 %tmp1,{{.*}} !prof ![[PROF1:[0-9]+]]
+
+bb5_1:
+ br label %bb5_2;
+
+bb5_2:
+ br label %bb5;
+
+bb2:
+ %tmp3 = call i32 @b()
+ %tmp4 = icmp ne i32 %tmp3, 1
+ br label %bb5
+; CHECK: br i1 %tmp4, {{.*}} !prof ![[PROF2:[0-9]+]]
+
+bb5:
+ %tmp6 = phi i1 [ false, %bb5_2 ], [ %tmp4, %bb2 ]
+ br i1 %tmp6, label %bb8, label %bb7, !prof !0
+
+bb7:
+ call void @bar()
+ br label %bb8
+
+bb8:
+ ret void
+}
+
+declare void @bar()
+
+declare i32 @a()
+
+declare i32 @b()
+
+!0 = !{!"branch_weights", i32 2146410443, i32 1073205}
+;CHECK: ![[PROF1]] = !{!"branch_weights", i32 1073205, i32 2146410443}
+;CHECK: ![[PROF2]] = !{!"branch_weights", i32 2146410443, i32 1073205}
Added: llvm/trunk/test/Transforms/JumpThreading/threading_prof2.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/JumpThreading/threading_prof2.ll?rev=311727&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/JumpThreading/threading_prof2.ll (added)
+++ llvm/trunk/test/Transforms/JumpThreading/threading_prof2.ll Thu Aug 24 15:54:01 2017
@@ -0,0 +1,42 @@
+; RUN: opt -jump-threading -S < %s | FileCheck %s
+; RUN: opt -passes=jump-threading -S < %s | FileCheck %s
+define void @test() {
+bb:
+ %tmp = call i32 @a()
+ %tmp1 = icmp eq i32 %tmp, 1
+ br i1 %tmp1, label %bb5, label %bb2
+; CHECK: br i1 %tmp1,{{.*}} !prof ![[PROF1:[0-9]+]]
+
+bb2:
+ %tmp3 = call i32 @b()
+ %tmp4 = icmp ne i32 %tmp3, 1
+ br label %bb5
+; CHECK: br i1 %tmp4, {{.*}} !prof ![[PROF2:[0-9]+]]
+
+bb5:
+ %tmp6 = phi i1 [ false, %bb ], [ %tmp4, %bb2 ]
+ br i1 %tmp6, label %bb8, label %bb7, !prof !0
+
+bb7:
+ call void @bar()
+ br label %bb9
+
+bb8:
+ call void @foo()
+ br label %bb9
+
+bb9:
+ ret void
+}
+
+declare void @bar()
+
+declare void @foo()
+
+declare i32 @a()
+
+declare i32 @b()
+
+!0 = !{!"branch_weights", i32 2146410443, i32 1073205}
+;CHECK: ![[PROF1]] = !{!"branch_weights", i32 1073205, i32 2146410443}
+;CHECK: ![[PROF2]] = !{!"branch_weights", i32 2146410443, i32 1073205}
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