[llvm-commits] [llvm] r132974 - in /llvm/trunk: lib/CodeGen/BranchFolding.cpp lib/CodeGen/BranchFolding.h test/CodeGen/X86/tail-threshold.ll
Rafael Espindola
rafael.espindola at gmail.com
Mon Jun 13 21:41:17 PDT 2011
Author: rafael
Date: Mon Jun 13 23:41:17 2011
New Revision: 132974
URL: http://llvm.org/viewvc/llvm-project?rev=132974&view=rev
Log:
Make the threshold used by branch folding softer. Before we would get a
sharp all or nothing transition when one extra predecessor was added. Now
we still test first ones for merging.
Added:
llvm/trunk/test/CodeGen/X86/tail-threshold.ll
Modified:
llvm/trunk/lib/CodeGen/BranchFolding.cpp
llvm/trunk/lib/CodeGen/BranchFolding.h
Modified: llvm/trunk/lib/CodeGen/BranchFolding.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/BranchFolding.cpp?rev=132974&r1=132973&r2=132974&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/BranchFolding.cpp (original)
+++ llvm/trunk/lib/CodeGen/BranchFolding.cpp Mon Jun 13 23:41:17 2011
@@ -799,14 +799,22 @@
// First find blocks with no successors.
MergePotentials.clear();
- for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
+ for (MachineFunction::iterator I = MF.begin(), E = MF.end();
+ I != E && MergePotentials.size() < TailMergeThreshold; ++I) {
+ if (TriedMerging.count(I))
+ continue;
if (I->succ_empty())
MergePotentials.push_back(MergePotentialsElt(HashEndOfMBB(I), I));
}
+ // If this is a large problem, avoid visiting the same basic blocks
+ // multiple times.
+ if (MergePotentials.size() == TailMergeThreshold)
+ for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i)
+ TriedMerging.insert(MergePotentials[i].getBlock());
+
// See if we can do any tail merging on those.
- if (MergePotentials.size() < TailMergeThreshold &&
- MergePotentials.size() >= 2)
+ if (MergePotentials.size() >= 2)
MadeChange |= TryTailMergeBlocks(NULL, NULL);
// Look at blocks (IBB) with multiple predecessors (PBB).
@@ -830,15 +838,17 @@
for (MachineFunction::iterator I = llvm::next(MF.begin()), E = MF.end();
I != E; ++I) {
- if (I->pred_size() >= 2 && I->pred_size() < TailMergeThreshold) {
+ if (I->pred_size() >= 2) {
SmallPtrSet<MachineBasicBlock *, 8> UniquePreds;
MachineBasicBlock *IBB = I;
MachineBasicBlock *PredBB = prior(I);
MergePotentials.clear();
for (MachineBasicBlock::pred_iterator P = I->pred_begin(),
E2 = I->pred_end();
- P != E2; ++P) {
+ P != E2 && MergePotentials.size() < TailMergeThreshold; ++P) {
MachineBasicBlock *PBB = *P;
+ if (TriedMerging.count(PBB))
+ continue;
// Skip blocks that loop to themselves, can't tail merge these.
if (PBB == IBB)
continue;
@@ -891,6 +901,12 @@
MergePotentials.push_back(MergePotentialsElt(HashEndOfMBB(PBB), *P));
}
}
+ // If this is a large problem, avoid visiting the same basic blocks
+ // multiple times.
+ if (MergePotentials.size() == TailMergeThreshold)
+ for (unsigned i = 0, e = MergePotentials.size(); i != e; ++i)
+ TriedMerging.insert(MergePotentials[i].getBlock());
+
if (MergePotentials.size() >= 2)
MadeChange |= TryTailMergeBlocks(IBB, PredBB);
// Reinsert an unconditional branch if needed.
Modified: llvm/trunk/lib/CodeGen/BranchFolding.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/BranchFolding.h?rev=132974&r1=132973&r2=132974&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/BranchFolding.h (original)
+++ llvm/trunk/lib/CodeGen/BranchFolding.h Mon Jun 13 23:41:17 2011
@@ -10,6 +10,7 @@
#ifndef LLVM_CODEGEN_BRANCHFOLDING_HPP
#define LLVM_CODEGEN_BRANCHFOLDING_HPP
+#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include <vector>
@@ -47,6 +48,7 @@
};
typedef std::vector<MergePotentialsElt>::iterator MPIterator;
std::vector<MergePotentialsElt> MergePotentials;
+ SmallPtrSet<const MachineBasicBlock*, 2> TriedMerging;
class SameTailElt {
MPIterator MPIter;
Added: llvm/trunk/test/CodeGen/X86/tail-threshold.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/tail-threshold.ll?rev=132974&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/X86/tail-threshold.ll (added)
+++ llvm/trunk/test/CodeGen/X86/tail-threshold.ll Mon Jun 13 23:41:17 2011
@@ -0,0 +1,41 @@
+; RUN: llc %s -stats -tail-merge-threshold 2 -o /dev/null |& FileCheck %s
+
+; Test that we still do some merging if a block has more than
+; tail-merge-threshold predecessors.
+
+; CHECK: 2 branchfolding - Number of block tails merged
+
+declare void @bar()
+
+define void @foo(i32 %xxx) {
+entry:
+ switch i32 %xxx, label %bb4 [
+ i32 0, label %bb0
+ i32 1, label %bb1
+ i32 2, label %bb2
+ i32 3, label %bb3
+ ]
+
+bb0:
+ call void @bar()
+ br label %bb5
+
+bb1:
+ call void @bar()
+ br label %bb5
+
+bb2:
+ call void @bar()
+ br label %bb5
+
+bb3:
+ call void @bar()
+ br label %bb5
+
+bb4:
+ call void @bar()
+ br label %bb5
+
+bb5:
+ ret void
+}
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