[llvm] r296818 - CodeGen: MachineBlockPlacement: Remove the unused outlining heuristic.
Kyle Butt via llvm-commits
llvm-commits at lists.llvm.org
Thu Mar 2 13:44:25 PST 2017
Author: iteratee
Date: Thu Mar 2 15:44:24 2017
New Revision: 296818
URL: http://llvm.org/viewvc/llvm-project?rev=296818&view=rev
Log:
CodeGen: MachineBlockPlacement: Remove the unused outlining heuristic.
Outlining optional branches isn't a good heuristic, and it's never been
on by default. Remove it to clean things up.
Removed:
llvm/trunk/test/CodeGen/X86/code_placement_outline_optional_branches.ll
Modified:
llvm/trunk/lib/CodeGen/MachineBlockPlacement.cpp
Modified: llvm/trunk/lib/CodeGen/MachineBlockPlacement.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/MachineBlockPlacement.cpp?rev=296818&r1=296817&r2=296818&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/MachineBlockPlacement.cpp (original)
+++ llvm/trunk/lib/CodeGen/MachineBlockPlacement.cpp Thu Mar 2 15:44:24 2017
@@ -36,7 +36,6 @@
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
#include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
-#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
@@ -86,19 +85,6 @@ static cl::opt<unsigned> ExitBlockBias(
// Definition:
// - Outlining: placement of a basic block outside the chain or hot path.
-static cl::opt<bool> OutlineOptionalBranches(
- "outline-optional-branches",
- cl::desc("Outlining optional branches will place blocks that are optional "
- "branches, i.e. branches with a common post dominator, outside "
- "the hot path or chain"),
- cl::init(false), cl::Hidden);
-
-static cl::opt<unsigned> OutlineOptionalThreshold(
- "outline-optional-threshold",
- cl::desc("Don't outline optional branches that are a single block with an "
- "instruction count below this threshold"),
- cl::init(4), cl::Hidden);
-
static cl::opt<unsigned> LoopToColdBlockRatio(
"loop-to-cold-block-ratio",
cl::desc("Outline loop blocks from loop chain if (frequency of loop) / "
@@ -335,9 +321,6 @@ class MachineBlockPlacement : public Mac
/// \brief A handle to the target's lowering info.
const TargetLoweringBase *TLI;
- /// \brief A handle to the dominator tree.
- MachineDominatorTree *MDT;
-
/// \brief A handle to the post dominator tree.
MachinePostDominatorTree *MPDT;
@@ -348,10 +331,6 @@ class MachineBlockPlacement : public Mac
/// must be done inline.
TailDuplicator TailDup;
- /// \brief A set of blocks that are unavoidably execute, i.e. they dominate
- /// all terminators of the MachineFunction.
- SmallPtrSet<const MachineBasicBlock *, 4> UnavoidableBlocks;
-
/// \brief Allocator and owner of BlockChain structures.
///
/// We build BlockChains lazily while processing the loop structure of
@@ -446,7 +425,6 @@ class MachineBlockPlacement : public Mac
void rotateLoopWithProfile(
BlockChain &LoopChain, const MachineLoop &L,
const BlockFilterSet &LoopBlockSet);
- void collectMustExecuteBBs();
void buildCFGChains();
void optimizeBranches();
void alignBlocks();
@@ -490,7 +468,6 @@ public:
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<MachineBranchProbabilityInfo>();
AU.addRequired<MachineBlockFrequencyInfo>();
- AU.addRequired<MachineDominatorTree>();
if (TailDupPlacement)
AU.addRequired<MachinePostDominatorTree>();
AU.addRequired<MachineLoopInfo>();
@@ -506,7 +483,6 @@ INITIALIZE_PASS_BEGIN(MachineBlockPlacem
"Branch Probability Basic Block Placement", false, false)
INITIALIZE_PASS_DEPENDENCY(MachineBranchProbabilityInfo)
INITIALIZE_PASS_DEPENDENCY(MachineBlockFrequencyInfo)
-INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
INITIALIZE_PASS_DEPENDENCY(MachinePostDominatorTree)
INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
INITIALIZE_PASS_END(MachineBlockPlacement, "block-placement",
@@ -1065,42 +1041,6 @@ bool MachineBlockPlacement::canTailDupli
return true;
}
-/// When the option OutlineOptionalBranches is on, this method
-/// checks if the fallthrough candidate block \p Succ (of block
-/// \p BB) also has other unscheduled predecessor blocks which
-/// are also successors of \p BB (forming triangular shape CFG).
-/// If none of such predecessors are small, it returns true.
-/// The caller can choose to select \p Succ as the layout successors
-/// so that \p Succ's predecessors (optional branches) can be
-/// outlined.
-/// FIXME: fold this with more general layout cost analysis.
-bool MachineBlockPlacement::shouldPredBlockBeOutlined(
- const MachineBasicBlock *BB, const MachineBasicBlock *Succ,
- const BlockChain &Chain, const BlockFilterSet *BlockFilter,
- BranchProbability SuccProb, BranchProbability HotProb) {
- if (!OutlineOptionalBranches)
- return false;
- // If we outline optional branches, look whether Succ is unavoidable, i.e.
- // dominates all terminators of the MachineFunction. If it does, other
- // successors must be optional. Don't do this for cold branches.
- if (SuccProb > HotProb.getCompl() && UnavoidableBlocks.count(Succ) > 0) {
- for (MachineBasicBlock *Pred : Succ->predecessors()) {
- // Check whether there is an unplaced optional branch.
- if (Pred == Succ || (BlockFilter && !BlockFilter->count(Pred)) ||
- BlockToChain[Pred] == &Chain)
- continue;
- // Check whether the optional branch has exactly one BB.
- if (Pred->pred_size() > 1 || *Pred->pred_begin() != BB)
- continue;
- // Check whether the optional branch is small.
- if (Pred->size() < OutlineOptionalThreshold)
- return false;
- }
- return true;
- } else
- return false;
-}
-
// When profile is not present, return the StaticLikelyProb.
// When profile is available, we need to handle the triangle-shape CFG.
static BranchProbability getLayoutSuccessorProbThreshold(
@@ -1357,13 +1297,6 @@ MachineBlockPlacement::selectBestSuccess
BranchProbability SuccProb =
getAdjustedProbability(RealSuccProb, AdjustedSumProb);
- // This heuristic is off by default.
- if (shouldPredBlockBeOutlined(BB, Succ, Chain, BlockFilter, SuccProb,
- HotProb)) {
- BestSucc.BB = Succ;
- return BestSucc;
- }
-
BlockChain &SuccChain = *BlockToChain[Succ];
// Skip the edge \c BB->Succ if block \c Succ has a better layout
// predecessor that yields lower global cost.
@@ -2131,31 +2064,6 @@ void MachineBlockPlacement::buildLoopCha
EHPadWorkList.clear();
}
-/// When OutlineOpitonalBranches is on, this method collects BBs that
-/// dominates all terminator blocks of the function \p F.
-void MachineBlockPlacement::collectMustExecuteBBs() {
- if (OutlineOptionalBranches) {
- // Find the nearest common dominator of all of F's terminators.
- MachineBasicBlock *Terminator = nullptr;
- for (MachineBasicBlock &MBB : *F) {
- if (MBB.succ_size() == 0) {
- if (Terminator == nullptr)
- Terminator = &MBB;
- else
- Terminator = MDT->findNearestCommonDominator(Terminator, &MBB);
- }
- }
-
- // MBBs dominating this common dominator are unavoidable.
- UnavoidableBlocks.clear();
- for (MachineBasicBlock &MBB : *F) {
- if (MDT->dominates(&MBB, Terminator)) {
- UnavoidableBlocks.insert(&MBB);
- }
- }
- }
-}
-
void MachineBlockPlacement::buildCFGChains() {
// Ensure that every BB in the function has an associated chain to simplify
// the assumptions of the remaining algorithm.
@@ -2190,9 +2098,6 @@ void MachineBlockPlacement::buildCFGChai
}
}
- // Turned on with OutlineOptionalBranches option
- collectMustExecuteBBs();
-
// Build any loop-based chains.
PreferredLoopExit = nullptr;
for (MachineLoop *L : *MLI)
@@ -2587,7 +2492,6 @@ bool MachineBlockPlacement::runOnMachine
MLI = &getAnalysis<MachineLoopInfo>();
TII = MF.getSubtarget().getInstrInfo();
TLI = MF.getSubtarget().getTargetLowering();
- MDT = &getAnalysis<MachineDominatorTree>();
MPDT = nullptr;
// Initialize PreferredLoopExit to nullptr here since it may never be set if
@@ -2624,8 +2528,7 @@ bool MachineBlockPlacement::runOnMachine
/*AfterBlockPlacement=*/true)) {
// Redo the layout if tail merging creates/removes/moves blocks.
BlockToChain.clear();
- // Must redo the dominator tree if blocks were changed.
- MDT->runOnMachineFunction(MF);
+ // Must redo the post-dominator tree if blocks were changed.
if (MPDT)
MPDT->runOnMachineFunction(MF);
ChainAllocator.DestroyAll();
Removed: llvm/trunk/test/CodeGen/X86/code_placement_outline_optional_branches.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/code_placement_outline_optional_branches.ll?rev=296817&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/X86/code_placement_outline_optional_branches.ll (original)
+++ llvm/trunk/test/CodeGen/X86/code_placement_outline_optional_branches.ll (removed)
@@ -1,77 +0,0 @@
-; RUN: llc -mcpu=corei7 -mtriple=x86_64-linux < %s | FileCheck %s
-; RUN: llc -mcpu=corei7 -mtriple=x86_64-linux -outline-optional-branches < %s | FileCheck %s -check-prefix=CHECK-OUTLINE
-
-define void @foo(i32 %t1, i32 %t2, i32 %t3) {
-; Test that we lift the call to 'c' up to immediately follow the call to 'b'
-; when we disable the cfg conflict check.
-;
-; CHECK-LABEL: foo:
-; CHECK: callq a
-; CHECK: callq a
-; CHECK: callq a
-; CHECK: callq a
-; CHECK: callq b
-; CHECK: callq c
-; CHECK: callq d
-; CHECK: callq e
-; CHECK: callq f
-;
-; CHECK-OUTLINE-LABEL: foo:
-; CHECK-OUTLINE: callq b
-; CHECK-OUTLINE: callq c
-; CHECK-OUTLINE: callq d
-; CHECK-OUTLINE: callq e
-; CHECK-OUTLINE: callq f
-; CHECK-OUTLINE: callq a
-; CHECK-OUTLINE: callq a
-; CHECK-OUTLINE: callq a
-; CHECK-OUTLINE: callq a
-
-entry:
- %cmp = icmp eq i32 %t1, 0
- br i1 %cmp, label %if.then, label %if.end
-
-if.then:
- call void @a()
- call void @a()
- call void @a()
- call void @a()
- br label %if.end
-
-if.end:
- call void @b()
- br label %hotbranch
-
-hotbranch:
- %cmp2 = icmp eq i32 %t2, 0
- br i1 %cmp2, label %if.then2, label %if.end2, !prof !1
-
-if.then2:
- call void @c()
- br label %if.end2
-
-if.end2:
- call void @d()
- br label %shortbranch
-
-shortbranch:
- %cmp3 = icmp eq i32 %t3, 0
- br i1 %cmp3, label %if.then3, label %if.end3
-
-if.then3:
- call void @e()
- br label %if.end3
-
-if.end3:
- call void @f()
- ret void
-}
-
-declare void @a()
-declare void @b()
-declare void @c()
-declare void @d()
-declare void @e()
-declare void @f()
-
-!1 = !{!"branch_weights", i32 64, i32 4}
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