[llvm] r200502 - PGO branch weight: update edge weights in SelectionDAGBuilder.
Manman Ren
manman.ren at gmail.com
Thu Jan 30 16:42:45 PST 2014
Author: mren
Date: Thu Jan 30 18:42:44 2014
New Revision: 200502
URL: http://llvm.org/viewvc/llvm-project?rev=200502&view=rev
Log:
PGO branch weight: update edge weights in SelectionDAGBuilder.
When converting from "or + br" to two branches, or converting from
"and + br" to two branches, we correctly update the edge weights of
the two branches.
The previous attempt at r200431 was reverted at r200434 because of
two testing case failures. I modified my patch a little, but forgot
to re-run "make check-all".
Testing case CodeGen/ARM/lsr-unfolded-offset.ll is updated because of
the patch's impact on branch probability which causes changes in
spill placement.
Added:
llvm/trunk/test/CodeGen/X86/MachineBranchProb.ll
Modified:
llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
llvm/trunk/test/CodeGen/ARM/lsr-unfolded-offset.ll
Modified: llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp?rev=200502&r1=200501&r2=200502&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp Thu Jan 30 18:42:44 2014
@@ -1393,7 +1393,9 @@ SelectionDAGBuilder::EmitBranchForMerged
MachineBasicBlock *TBB,
MachineBasicBlock *FBB,
MachineBasicBlock *CurBB,
- MachineBasicBlock *SwitchBB) {
+ MachineBasicBlock *SwitchBB,
+ uint32_t TWeight,
+ uint32_t FWeight) {
const BasicBlock *BB = CurBB->getBasicBlock();
// If the leaf of the tree is a comparison, merge the condition into
@@ -1418,7 +1420,7 @@ SelectionDAGBuilder::EmitBranchForMerged
}
CaseBlock CB(Condition, BOp->getOperand(0),
- BOp->getOperand(1), NULL, TBB, FBB, CurBB);
+ BOp->getOperand(1), NULL, TBB, FBB, CurBB, TWeight, FWeight);
SwitchCases.push_back(CB);
return;
}
@@ -1426,17 +1428,26 @@ SelectionDAGBuilder::EmitBranchForMerged
// Create a CaseBlock record representing this branch.
CaseBlock CB(ISD::SETEQ, Cond, ConstantInt::getTrue(*DAG.getContext()),
- NULL, TBB, FBB, CurBB);
+ NULL, TBB, FBB, CurBB, TWeight, FWeight);
SwitchCases.push_back(CB);
}
+/// Scale down both weights to fit into uint32_t.
+static void ScaleWeights(uint64_t &NewTrue, uint64_t &NewFalse) {
+ uint64_t NewMax = (NewTrue > NewFalse) ? NewTrue : NewFalse;
+ uint32_t Scale = (NewMax / UINT32_MAX) + 1;
+ NewTrue = NewTrue / Scale;
+ NewFalse = NewFalse / Scale;
+}
+
/// FindMergedConditions - If Cond is an expression like
void SelectionDAGBuilder::FindMergedConditions(const Value *Cond,
MachineBasicBlock *TBB,
MachineBasicBlock *FBB,
MachineBasicBlock *CurBB,
MachineBasicBlock *SwitchBB,
- unsigned Opc) {
+ unsigned Opc, uint32_t TWeight,
+ uint32_t FWeight) {
// If this node is not part of the or/and tree, emit it as a branch.
const Instruction *BOp = dyn_cast<Instruction>(Cond);
if (!BOp || !(isa<BinaryOperator>(BOp) || isa<CmpInst>(BOp)) ||
@@ -1444,7 +1455,8 @@ void SelectionDAGBuilder::FindMergedCond
BOp->getParent() != CurBB->getBasicBlock() ||
!InBlock(BOp->getOperand(0), CurBB->getBasicBlock()) ||
!InBlock(BOp->getOperand(1), CurBB->getBasicBlock())) {
- EmitBranchForMergedCondition(Cond, TBB, FBB, CurBB, SwitchBB);
+ EmitBranchForMergedCondition(Cond, TBB, FBB, CurBB, SwitchBB,
+ TWeight, FWeight);
return;
}
@@ -1456,6 +1468,7 @@ void SelectionDAGBuilder::FindMergedCond
if (Opc == Instruction::Or) {
// Codegen X | Y as:
+ // BB1:
// jmp_if_X TBB
// jmp TmpBB
// TmpBB:
@@ -1463,14 +1476,34 @@ void SelectionDAGBuilder::FindMergedCond
// jmp FBB
//
+ // We have flexibility in setting Prob for BB1 and Prob for TmpBB.
+ // The requirement is that
+ // TrueProb for BB1 + (FalseProb for BB1 * TrueProb for TmpBB)
+ // = TrueProb for orignal BB.
+ // Assuming the orignal weights are A and B, one choice is to set BB1's
+ // weights to A and A+2B, and set TmpBB's weights to A and 2B. This choice
+ // assumes that
+ // TrueProb for BB1 == FalseProb for BB1 * TrueProb for TmpBB.
+ // Another choice is to assume TrueProb for BB1 equals to TrueProb for
+ // TmpBB, but the math is more complicated.
+
+ uint64_t NewTrueWeight = TWeight;
+ uint64_t NewFalseWeight = (uint64_t)TWeight + 2 * (uint64_t)FWeight;
+ ScaleWeights(NewTrueWeight, NewFalseWeight);
// Emit the LHS condition.
- FindMergedConditions(BOp->getOperand(0), TBB, TmpBB, CurBB, SwitchBB, Opc);
+ FindMergedConditions(BOp->getOperand(0), TBB, TmpBB, CurBB, SwitchBB, Opc,
+ NewTrueWeight, NewFalseWeight);
+ NewTrueWeight = TWeight;
+ NewFalseWeight = 2 * (uint64_t)FWeight;
+ ScaleWeights(NewTrueWeight, NewFalseWeight);
// Emit the RHS condition into TmpBB.
- FindMergedConditions(BOp->getOperand(1), TBB, FBB, TmpBB, SwitchBB, Opc);
+ FindMergedConditions(BOp->getOperand(1), TBB, FBB, TmpBB, SwitchBB, Opc,
+ NewTrueWeight, NewFalseWeight);
} else {
assert(Opc == Instruction::And && "Unknown merge op!");
// Codegen X & Y as:
+ // BB1:
// jmp_if_X TmpBB
// jmp FBB
// TmpBB:
@@ -1479,11 +1512,28 @@ void SelectionDAGBuilder::FindMergedCond
//
// This requires creation of TmpBB after CurBB.
+ // We have flexibility in setting Prob for BB1 and Prob for TmpBB.
+ // The requirement is that
+ // FalseProb for BB1 + (TrueProb for BB1 * FalseProb for TmpBB)
+ // = FalseProb for orignal BB.
+ // Assuming the orignal weights are A and B, one choice is to set BB1's
+ // weights to 2A+B and B, and set TmpBB's weights to 2A and B. This choice
+ // assumes that
+ // FalseProb for BB1 == TrueProb for BB1 * FalseProb for TmpBB.
+
+ uint64_t NewTrueWeight = 2 * (uint64_t)TWeight + (uint64_t)FWeight;
+ uint64_t NewFalseWeight = FWeight;
+ ScaleWeights(NewTrueWeight, NewFalseWeight);
// Emit the LHS condition.
- FindMergedConditions(BOp->getOperand(0), TmpBB, FBB, CurBB, SwitchBB, Opc);
+ FindMergedConditions(BOp->getOperand(0), TmpBB, FBB, CurBB, SwitchBB, Opc,
+ NewTrueWeight, NewFalseWeight);
+ NewTrueWeight = 2 * (uint64_t)TWeight;
+ NewFalseWeight = FWeight;
+ ScaleWeights(NewTrueWeight, NewFalseWeight);
// Emit the RHS condition into TmpBB.
- FindMergedConditions(BOp->getOperand(1), TBB, FBB, TmpBB, SwitchBB, Opc);
+ FindMergedConditions(BOp->getOperand(1), TBB, FBB, TmpBB, SwitchBB, Opc,
+ NewTrueWeight, NewFalseWeight);
}
}
@@ -1570,7 +1620,8 @@ void SelectionDAGBuilder::visitBr(const
(BOp->getOpcode() == Instruction::And ||
BOp->getOpcode() == Instruction::Or)) {
FindMergedConditions(BOp, Succ0MBB, Succ1MBB, BrMBB, BrMBB,
- BOp->getOpcode());
+ BOp->getOpcode(), getEdgeWeight(BrMBB, Succ0MBB),
+ getEdgeWeight(BrMBB, Succ1MBB));
// If the compares in later blocks need to use values not currently
// exported from this block, export them now. This block should always
// be the first entry.
Modified: llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h?rev=200502&r1=200501&r2=200502&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.h Thu Jan 30 18:42:44 2014
@@ -612,11 +612,13 @@ public:
void FindMergedConditions(const Value *Cond, MachineBasicBlock *TBB,
MachineBasicBlock *FBB, MachineBasicBlock *CurBB,
- MachineBasicBlock *SwitchBB, unsigned Opc);
+ MachineBasicBlock *SwitchBB, unsigned Opc,
+ uint32_t TW, uint32_t FW);
void EmitBranchForMergedCondition(const Value *Cond, MachineBasicBlock *TBB,
MachineBasicBlock *FBB,
MachineBasicBlock *CurBB,
- MachineBasicBlock *SwitchBB);
+ MachineBasicBlock *SwitchBB,
+ uint32_t TW, uint32_t FW);
bool ShouldEmitAsBranches(const std::vector<CaseBlock> &Cases);
bool isExportableFromCurrentBlock(const Value *V, const BasicBlock *FromBB);
void CopyToExportRegsIfNeeded(const Value *V);
Modified: llvm/trunk/test/CodeGen/ARM/lsr-unfolded-offset.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/ARM/lsr-unfolded-offset.ll?rev=200502&r1=200501&r2=200502&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/ARM/lsr-unfolded-offset.ll (original)
+++ llvm/trunk/test/CodeGen/ARM/lsr-unfolded-offset.ll Thu Jan 30 18:42:44 2014
@@ -4,7 +4,7 @@
; register pressure and therefore spilling. There is more room for improvement
; here.
-; CHECK: sub sp, #{{40|32|28|24}}
+; CHECK: sub sp, #{{40|36|32|28|24}}
; CHECK: %for.inc
; CHECK-NOT: ldr
Added: llvm/trunk/test/CodeGen/X86/MachineBranchProb.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/MachineBranchProb.ll?rev=200502&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/X86/MachineBranchProb.ll (added)
+++ llvm/trunk/test/CodeGen/X86/MachineBranchProb.ll Thu Jan 30 18:42:44 2014
@@ -0,0 +1,34 @@
+; RUN: llc < %s -mtriple=x86_64-apple-darwin -print-machineinstrs=expand-isel-pseudos -o /dev/null 2>&1 | FileCheck %s
+
+;; Make sure a transformation in SelectionDAGBuilder that converts "or + br" to
+;; two branches correctly updates the branch probability.
+
+ at max_regno = common global i32 0, align 4
+
+define void @test(i32* %old, i32 %final) {
+for.cond:
+ br label %for.cond2
+
+for.cond2: ; preds = %for.inc, %for.cond
+ %i.1 = phi i32 [ %inc19, %for.inc ], [ 0, %for.cond ]
+ %bit.0 = phi i32 [ %shl, %for.inc ], [ 1, %for.cond ]
+ %tobool = icmp eq i32 %bit.0, 0
+ %v3 = load i32* @max_regno, align 4
+ %cmp4 = icmp eq i32 %i.1, %v3
+ %or.cond = or i1 %tobool, %cmp4
+ br i1 %or.cond, label %for.inc20, label %for.inc, !prof !0
+; CHECK: BB#1: derived from LLVM BB %for.cond2
+; CHECK: Successors according to CFG: BB#3(56008718) BB#4(2203492365)
+; CHECK: BB#4: derived from LLVM BB %for.cond2
+; CHECK: Successors according to CFG: BB#3(112017436) BB#2(4294967294)
+
+for.inc: ; preds = %for.cond2
+ %shl = shl i32 %bit.0, 1
+ %inc19 = add nsw i32 %i.1, 1
+ br label %for.cond2
+
+for.inc20: ; preds = %for.cond2
+ ret void
+}
+
+!0 = metadata !{metadata !"branch_weights", i32 112017436, i32 -735157296}
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