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Make CanFallThrough more intelligent (so it can handle blocks with (e.g.) no

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successors), and make island block movement more general.

This compiles CodeGen/X86/2006-04-27-ISelFoldingBug.ll to:

_loadAndRLEsource_no_exit_2E_1_label_2E_0:
        subl $8, %esp
        movl %esi, 4(%esp)
        movl %ebx, (%esp)
        movl 16(%esp), %eax
        movl 12(%esp), %ecx
LBB1_3: #label.0
        movl _last, %edx
        movl %edx, %esi
        incl %esi
        movl %esi, _last
        movl %ecx, %ebx
        # TRUNCATE movb %bl, %bl
        movl _block, %esi
        movb %bl, 1(%esi,%edx)
        cmpl %eax, _last
        jge LBB1_2      #codeRepl5.exitStub
LBB1_4: #label.0
        cmpl $257, %ecx
        je LBB1_2       #codeRepl5.exitStub
LBB1_1: #label.0.no_exit.1_crit_edge.exitStub
        movl $1, %eax
        movl (%esp), %ebx
        movl 4(%esp), %esi
        addl $8, %esp
        ret
LBB1_2: #codeRepl5.exitStub
        xorl %eax, %eax
        movl (%esp), %ebx
        movl 4(%esp), %esi
        addl $8, %esp
        ret

instead of:

_loadAndRLEsource_no_exit_2E_1_label_2E_0:
        subl $8, %esp
        movl %esi, 4(%esp)
        movl %ebx, (%esp)
        movl 16(%esp), %eax
        movl 12(%esp), %ecx
        jmp LBB1_3      #label.0
LBB1_1: #label.0.no_exit.1_crit_edge.exitStub
        movl $1, %eax
        movl (%esp), %ebx
        movl 4(%esp), %esi
        addl $8, %esp
        ret
LBB1_2: #codeRepl5.exitStub
        xorl %eax, %eax
        movl (%esp), %ebx
        movl 4(%esp), %esi
        addl $8, %esp
        ret
LBB1_3: #label.0
        movl _last, %edx
        movl %edx, %esi
        incl %esi
        movl %esi, _last
        movl %ecx, %ebx
        # TRUNCATE movb %bl, %bl
        movl _block, %esi
        movb %bl, 1(%esi,%edx)
        cmpl %eax, _last
        jge LBB1_2      #codeRepl5.exitStub
LBB1_4: #label.0
        cmpl $257, %ecx
        jne LBB1_1      #label.0.no_exit.1_crit_edge.exitStub
        jmp LBB1_2      #codeRepl5.exitStub

... which is much better layout :)


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@31282 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2006-10-29 21:05:41 +00:00
parent 6a586c8d9a
commit 6b0e3f8907
1 changed files with 96 additions and 64 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

82
lib/CodeGen/BranchFolding.cpp
View File

@ -48,6 +48,11 @@ namespace {
bool OptimizeBranches(MachineFunction &MF);
void OptimizeBlock(MachineBasicBlock *MBB);
void RemoveDeadBlock(MachineBasicBlock *MBB);
bool CanFallThrough(MachineBasicBlock *CurBB);
bool CanFallThrough(MachineBasicBlock *CurBB, bool BranchUnAnalyzable,
MachineBasicBlock *TBB, MachineBasicBlock *FBB,
const std::vector<MachineOperand> &Cond);
};
}
@ -443,19 +448,37 @@ static void ReplaceUsesOfBlockWith(MachineBasicBlock *BB,
}
}
/// CanFallThrough - Return true of the specified branch condition can transfer
/// control to FallthroughBlock, the block immediately after the branch.
static bool CanFallThrough(MachineBasicBlock *TBB,
MachineBasicBlock *FBB,
const std::vector<MachineOperand> &Cond,
MachineFunction::iterator FallthroughBlock) {
/// CanFallThrough - Return true if the specified block (with the specified
/// branch condition) can implicitly transfer control to the block after it by
/// falling off the end of it. This should return false if it can reach the
/// block after it, but it uses an explicit branch to do so (e.g. a table jump).
///
/// True is a conservative answer.
///
bool BranchFolder::CanFallThrough(MachineBasicBlock *CurBB,
bool BranchUnAnalyzable,
MachineBasicBlock *TBB, MachineBasicBlock *FBB,
const std::vector<MachineOperand> &Cond) {
MachineFunction::iterator Fallthrough = CurBB;
++Fallthrough;
// If FallthroughBlock is off the end of the function, it can't fall through.
if (Fallthrough == CurBB->getParent()->end())
return false;
// If FallthroughBlock isn't a successor of CurBB, no fallthrough is possible.
if (!CurBB->isSuccessor(Fallthrough))
return false;
// If we couldn't analyze the branch, assume it could fall through.
if (BranchUnAnalyzable) return true;
// If there is no branch, control always falls through.
if (TBB == 0) return true;
// If there is some explicit branch to the fallthrough block, it can obviously
// reach, even though the branch should get folded to fall through implicitly.
if (MachineFunction::iterator(TBB) == FallthroughBlock ||
MachineFunction::iterator(FBB) == FallthroughBlock)
if (MachineFunction::iterator(TBB) == Fallthrough ||
MachineFunction::iterator(FBB) == Fallthrough)
return true;
// If it's an unconditional branch to some block not the fall through, it
@ -467,6 +490,20 @@ static bool CanFallThrough(MachineBasicBlock *TBB,
return FBB == 0;
}
/// CanFallThrough - Return true if the specified can implicitly transfer
/// control to the block after it by falling off the end of it. This should
/// return false if it can reach the block after it, but it uses an explicit
/// branch to do so (e.g. a table jump).
///
/// True is a conservative answer.
///
bool BranchFolder::CanFallThrough(MachineBasicBlock *CurBB) {
MachineBasicBlock *TBB = 0, *FBB = 0;
std::vector<MachineOperand> Cond;
bool CurUnAnalyzable = TII->AnalyzeBranch(*CurBB, TBB, FBB, Cond);
return CanFallThrough(CurBB, CurUnAnalyzable, TBB, FBB, Cond);
}
/// OptimizeBlock - Analyze and optimize control flow related to the specified
/// block. This is never called on the entry block.
void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) {
@ -504,8 +541,8 @@ void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) {
MachineBasicBlock *PriorTBB = 0, *PriorFBB = 0;
std::vector<MachineOperand> PriorCond;
bool PriorUnAnalyzable = false;
PriorUnAnalyzable = TII->AnalyzeBranch(PrevBB, PriorTBB, PriorFBB, PriorCond);
bool PriorUnAnalyzable =
TII->AnalyzeBranch(PrevBB, PriorTBB, PriorFBB, PriorCond);
if (!PriorUnAnalyzable) {
// If the CFG for the prior block has extra edges, remove them.
MadeChange |= CorrectExtraCFGEdges(PrevBB, PriorTBB, PriorFBB,
@ -561,7 +598,8 @@ void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) {
// Analyze the branch in the current block.
MachineBasicBlock *CurTBB = 0, *CurFBB = 0;
std::vector<MachineOperand> CurCond;
if (!TII->AnalyzeBranch(*MBB, CurTBB, CurFBB, CurCond)) {
bool CurUnAnalyzable = TII->AnalyzeBranch(*MBB, CurTBB, CurFBB, CurCond);
if (!CurUnAnalyzable) {
// If the CFG for the prior block has extra edges, remove them.
MadeChange |= CorrectExtraCFGEdges(*MBB, CurTBB, CurFBB,
!CurCond.empty(),
@ -630,16 +668,16 @@ void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) {
// Add the branch back if the block is more than just an uncond branch.
TII->InsertBranch(*MBB, CurTBB, 0, CurCond);
}
}
// If the prior block doesn't fall through into this block, and if this
// block doesn't fall through into some other block, see if we can find a
// place to move this block where a fall-through will happen.
if (!PriorUnAnalyzable && !CanFallThrough(PriorTBB, PriorFBB,
PriorCond, MBB)) {
if (!CanFallThrough(&PrevBB, PriorUnAnalyzable,
PriorTBB, PriorFBB, PriorCond)) {
// Now we know that there was no fall-through into this block, check to
// see if it has fall-throughs.
if (!CanFallThrough(CurTBB, CurFBB, CurCond, FallThrough)) {
// see if it has a fall-through into its successor.
if (!CanFallThrough(MBB, CurUnAnalyzable, CurTBB, CurFBB, CurCond)) {
// Check all the predecessors of this block. If one of them has no fall
// throughs, move this block right after it.
for (MachineBasicBlock::pred_iterator PI = MBB->pred_begin(),
@ -649,9 +687,7 @@ void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) {
MachineFunction::iterator PredFallthrough = PredBB; ++PredFallthrough;
MachineBasicBlock *PredTBB = 0, *PredFBB = 0;
std::vector<MachineOperand> PredCond;
if (PredBB != MBB &&
!TII->AnalyzeBranch(*PredBB, PredTBB, PredFBB, PredCond) &&
!CanFallThrough(PredTBB, PredFBB, PredCond, PredFallthrough)) {
if (PredBB != MBB && !CanFallThrough(PredBB)) {
MBB->moveAfter(PredBB);
MadeChange = true;
return OptimizeBlock(MBB);
@ -666,10 +702,7 @@ void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) {
MachineFunction::iterator SuccPrev = SuccBB; --SuccPrev;
MachineBasicBlock *SuccPrevTBB = 0, *SuccPrevFBB = 0;
std::vector<MachineOperand> SuccPrevCond;
if (SuccBB != MBB &&
!TII->AnalyzeBranch(*SuccPrev, SuccPrevTBB, SuccPrevFBB,
SuccPrevCond) &&
!CanFallThrough(SuccPrevTBB, SuccPrevFBB, SuccPrevCond, SuccBB)) {
if (SuccBB != MBB && !CanFallThrough(SuccPrev)) {
MBB->moveBefore(SuccBB);
MadeChange = true;
return OptimizeBlock(MBB);
@ -680,12 +713,11 @@ void BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) {
// the block before this one would be a fall-through if this block were
// removed, move this block to the end of the function.
if (FallThrough != MBB->getParent()->end() &&
CanFallThrough(PriorTBB, PriorFBB, PriorCond, FallThrough)) {
PrevBB.isSuccessor(FallThrough)) {
MBB->moveAfter(--MBB->getParent()->end());
MadeChange = true;
return;
}
}
}
}
}