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Handle some non-exit blocks in tail merging.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@36907 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dale Johannesen 2007-05-07 20:57:21 +00:00
parent 4fee7034d5
commit 7d33b4c59b
2 changed files with 146 additions and 11 deletions
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92
lib/CodeGen/BranchFolding.cpp
View File

@ -50,11 +50,14 @@ namespace {
private:
// Tail Merging.
bool TailMergeBlocks(MachineFunction &MF);
bool TryMergeBlocks(MachineBasicBlock* SuccBB,
MachineBasicBlock* PredBB);
void ReplaceTailWithBranchTo(MachineBasicBlock::iterator OldInst,
MachineBasicBlock *NewDest);
MachineBasicBlock *SplitMBBAt(MachineBasicBlock &CurMBB,
MachineBasicBlock::iterator BBI1);
std::vector<std::pair<unsigned,MachineBasicBlock*> > MergePotentials;
const MRegisterInfo *RegInfo;
RegScavenger *RS;
// Branch optzn.
@ -346,18 +349,18 @@ static bool ShouldSplitFirstBlock(MachineBasicBlock *MBB1,
return MBB1Time < MBB2Time;
}
bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
// See if any of the blocks in MergePotentials (which all have a common single
// successor, or all have no successor) can be tail-merged. If there is a
// successor, any blocks in MergePotentials that are not tail-merged and
// are not immediately before Succ must have an unconditional branch to
// Succ added (but the predecessor/successor lists need no adjustment).
// The lone predecessor of Succ that falls through into Succ,
// if any, is given in PredBB.
bool BranchFolder::TryMergeBlocks(MachineBasicBlock *SuccBB,
MachineBasicBlock* PredBB) {
MadeChange = false;
if (!EnableTailMerge) return false;
// Find blocks with no successors.
std::vector<std::pair<unsigned,MachineBasicBlock*> > MergePotentials;
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
if (I->succ_empty())
MergePotentials.push_back(std::make_pair(HashEndOfMBB(I), I));
}
// Sort by hash value so that blocks with identical end sequences sort
// together.
std::stable_sort(MergePotentials.begin(), MergePotentials.end());
@ -371,6 +374,8 @@ bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
// If there is nothing that matches the hash of the current basic block,
// give up.
if (CurHash != PrevHash) {
if (SuccBB && CurMBB != PredBB)
TII->InsertBranch(*CurMBB, SuccBB, NULL, std::vector<MachineOperand>());
MergePotentials.pop_back();
continue;
}
@ -401,6 +406,9 @@ bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
// If we didn't find anything that has at least two instructions matching
// this one, bail out.
if (FoundMatch == ~0U) {
// Put the unconditional branch back, if we need one.
if (SuccBB && CurMBB != PredBB)
TII->InsertBranch(*CurMBB, SuccBB, NULL, std::vector<MachineOperand>());
MergePotentials.pop_back();
continue;
}
@ -445,10 +453,72 @@ bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
}
MadeChange = true;
}
return MadeChange;
}
bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
MadeChange = false;
if (!EnableTailMerge) return false;
// First find blocks with no successors.
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
if (I->succ_empty())
MergePotentials.push_back(std::make_pair(HashEndOfMBB(I), I));
}
// See if we can do any crossjumping on those.
MadeChange |= TryMergeBlocks(NULL, NULL);
MergePotentials.clear();
// Look at blocks with two predecessors, where each predecessor has either:
// - a single successor, or
// - two successors, where successor I is reached either by ubr or fallthrough.
// The two-successor case where successor I is reached by cbr
// from both blocks is handled by the preceding case (when we consider the
// other, fallthough block).
// FIXME: The two-successor case where I is reached by cbr
// from one block, and by fallthrough/ubr from the other, is not handled yet.
// Beware that sometimes blocks are in the predecessor list, but can't really
// jump to the "successor" we're looking at. Tolerate this.
for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
if (!I->succ_empty() && I->pred_size() >= 2) {
MachineBasicBlock *IBB = I;
MachineBasicBlock *PredBB = prior(I);
for (MachineBasicBlock::pred_iterator P = I->pred_begin(), E2 = I->pred_end();
P != E2; ++P) {
MachineBasicBlock* PBB = *P;
MachineBasicBlock *TBB = 0, *FBB = 0;
std::vector<MachineOperand> Cond;
// Remove the unconditional branch at the end, if any.
if (!TII->AnalyzeBranch(*PBB, TBB, FBB, Cond) &&
((!FBB && Cond.size()==0) || // single successor
(!FBB && TBB!=IBB) || // cbr elsewhere, fallthrough to I
(FBB && FBB==IBB))) { // cbr then branch to I
if (TBB) {
TII->RemoveBranch(*PBB);
if (TBB!=IBB)
// reinsert conditional branch only, for now
TII->InsertBranch(*PBB, TBB, 0, Cond);
}
MergePotentials.push_back(std::make_pair(HashEndOfMBB(PBB), *P));
}
}
if (MergePotentials.size() >= 2)
MadeChange |= TryMergeBlocks(I, PredBB);
// Reinsert an unconditional branch if needed.
// The 1 below can be either an original single predecessor, or a result
// of removing blocks in TryMergeBlocks.
if (MergePotentials.size()==1 &&
(MergePotentials.begin())->second != PredBB)
TII->InsertBranch(*((MergePotentials.begin())->second), I, NULL,
std::vector<MachineOperand>());
MergePotentials.clear();
}
}
return MadeChange;
}
//===----------------------------------------------------------------------===//
// Branch Optimization

65
test/CodeGen/Generic/2007-05-07-tailmerge-1.c Normal file
View File

@ -0,0 +1,65 @@
; RUN: llvm-as < %s | llc -march=arm -enable-tail-merge | grep bl.*baz | wc -l | grep 1
; RUN: llvm-as < %s | llc -march=arm -enable-tail-merge | grep bl.*quux | wc -l | grep 1
; Check that calls to baz and quux are tail-merged.
; ModuleID = 'tail.c'
target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64"
target triple = "i686-apple-darwin8"
define i32 @f(i32 %i, i32 %q) {
entry:
%i_addr = alloca i32 ; <i32*> [#uses=2]
%q_addr = alloca i32 ; <i32*> [#uses=2]
%retval = alloca i32, align 4 ; <i32*> [#uses=1]
"alloca point" = bitcast i32 0 to i32 ; <i32> [#uses=0]
store i32 %i, i32* %i_addr
store i32 %q, i32* %q_addr
%tmp = load i32* %i_addr ; <i32> [#uses=1]
%tmp1 = icmp ne i32 %tmp, 0 ; <i1> [#uses=1]
%tmp12 = zext i1 %tmp1 to i8 ; <i8> [#uses=1]
%toBool = icmp ne i8 %tmp12, 0 ; <i1> [#uses=1]
br i1 %toBool, label %cond_true, label %cond_false
cond_true: ; preds = %entry
%tmp3 = call i32 (...)* @bar( ) ; <i32> [#uses=0]
%tmp4 = call i32 (...)* @baz( i32 5, i32 6 ) ; <i32> [#uses=0]
br label %cond_next
cond_false: ; preds = %entry
%tmp5 = call i32 (...)* @foo( ) ; <i32> [#uses=0]
%tmp6 = call i32 (...)* @baz( i32 5, i32 6 ) ; <i32> [#uses=0]
br label %cond_next
cond_next: ; preds = %cond_false, %cond_true
%tmp7 = load i32* %q_addr ; <i32> [#uses=1]
%tmp8 = icmp ne i32 %tmp7, 0 ; <i1> [#uses=1]
%tmp89 = zext i1 %tmp8 to i8 ; <i8> [#uses=1]
%toBool10 = icmp ne i8 %tmp89, 0 ; <i1> [#uses=1]
br i1 %toBool10, label %cond_true11, label %cond_false15
cond_true11: ; preds = %cond_next
%tmp13 = call i32 (...)* @foo( ) ; <i32> [#uses=0]
%tmp14 = call i32 (...)* @quux( i32 3, i32 4 ) ; <i32> [#uses=0]
br label %cond_next18
cond_false15: ; preds = %cond_next
%tmp16 = call i32 (...)* @bar( ) ; <i32> [#uses=0]
%tmp17 = call i32 (...)* @quux( i32 3, i32 4 ) ; <i32> [#uses=0]
br label %cond_next18
cond_next18: ; preds = %cond_false15, %cond_true11
%tmp19 = call i32 (...)* @bar( ) ; <i32> [#uses=0]
br label %return
return: ; preds = %cond_next18
%retval20 = load i32* %retval ; <i32> [#uses=1]
ret i32 %retval20
}
declare i32 @bar(...)
declare i32 @baz(...)
declare i32 @foo(...)
declare i32 @quux(...)