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Teach inst combine to merge GEPs through PHIs. This is really 

important because it is sinking the loads using the GEPs, but
not the GEPs themselves.  This triggers 647 times on 403.gcc
and makes the .s file much much nicer.  For example before:

        je      LBB1_87 ## bb78
LBB1_62:        ## bb77
        leal    84(%esi), %eax
LBB1_63:        ## bb79
        movl    (%eax), %eax
...
LBB1_87:        ## bb78
        movl    $0, 4(%esp)
        movl    %esi, (%esp)
        call    L_make_decl_rtl$stub
        jmp     LBB1_62 ## bb77


after:

        jne     LBB1_63 ## bb79
LBB1_62:        ## bb78
        movl    $0, 4(%esp)
        movl    %esi, (%esp)
        call    L_make_decl_rtl$stub
LBB1_63:        ## bb79
        movl    84(%esi), %eax

The input code was (and the GEPs are merged and
the PHI is now eliminated by instcombine):

        br i1 %tmp233, label %bb78, label %bb77
bb77:           
        %tmp234 = getelementptr %struct.tree_node* %t_addr.3, i32 0, i32 0, i32 22              
        br label %bb79
bb78:           
        call void @make_decl_rtl(%struct.tree_node* %t_addr.3, i8* null) nounwind
        %tmp235 = getelementptr %struct.tree_node* %t_addr.3, i32 0, i32 0, i32 22              
        br label %bb79
bb79:           
        %iftmp.12.0.in = phi %struct.rtx_def** [ %tmp235, %bb78 ], [ %tmp234, %bb77 ]           
        %iftmp.12.0 = load %struct.rtx_def** %iftmp.12.0.in             

llvm-svn: 60322
This commit is contained in:
Chris Lattner 2008-12-01 02:34:36 +00:00
parent c9687907c5
commit 9d02a70a7d
2 changed files with 111 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

113
llvm/lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -372,7 +372,8 @@ namespace {
// inputs, and do the operation once, to the result of the PHI.
Instruction *FoldPHIArgOpIntoPHI(PHINode &PN);
Instruction *FoldPHIArgBinOpIntoPHI(PHINode &PN);
Instruction *FoldPHIArgGEPIntoPHI(PHINode &PN);
Instruction *OptAndOp(Instruction *Op, ConstantInt *OpRHS,
ConstantInt *AndRHS, BinaryOperator &TheAnd);
@ -9985,7 +9986,7 @@ Instruction *InstCombiner::FoldPHIArgBinOpIntoPHI(PHINode &PN) {
// Scan to see if all operands are the same opcode, all have one use, and all
// kill their operands (i.e. the operands have one use).
for (unsigned i = 0; i != PN.getNumIncomingValues(); ++i) {
for (unsigned i = 1; i != PN.getNumIncomingValues(); ++i) {
Instruction *I = dyn_cast<Instruction>(PN.getIncomingValue(i));
if (!I || I->getOpcode() != Opc || !I->hasOneUse() ||
// Verify type of the LHS matches so we don't fold cmp's of different
@ -10010,6 +10011,7 @@ Instruction *InstCombiner::FoldPHIArgBinOpIntoPHI(PHINode &PN) {
// If this is a GEP, and if the index (not the pointer) needs a PHI, bail out.
// Indexes are often folded into load/store instructions, so we don't want to
// hide them behind a phi.
// URR??
if (isa<GetElementPtrInst>(FirstInst) && RHSVal == 0)
return 0;
@ -10035,28 +10037,101 @@ Instruction *InstCombiner::FoldPHIArgBinOpIntoPHI(PHINode &PN) {
}
// Add all operands to the new PHIs.
for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) {
if (NewLHS) {
Value *NewInLHS =cast<Instruction>(PN.getIncomingValue(i))->getOperand(0);
NewLHS->addIncoming(NewInLHS, PN.getIncomingBlock(i));
}
if (NewRHS) {
Value *NewInRHS =cast<Instruction>(PN.getIncomingValue(i))->getOperand(1);
NewRHS->addIncoming(NewInRHS, PN.getIncomingBlock(i));
if (NewLHS || NewRHS) {
for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) {
Instruction *InInst = cast<Instruction>(PN.getIncomingValue(i));
if (NewLHS) {
Value *NewInLHS = InInst->getOperand(0);
NewLHS->addIncoming(NewInLHS, PN.getIncomingBlock(i));
}
if (NewRHS) {
Value *NewInRHS = InInst->getOperand(1);
NewRHS->addIncoming(NewInRHS, PN.getIncomingBlock(i));
}
}
}
if (BinaryOperator *BinOp = dyn_cast<BinaryOperator>(FirstInst))
return BinaryOperator::Create(BinOp->getOpcode(), LHSVal, RHSVal);
else if (CmpInst *CIOp = dyn_cast<CmpInst>(FirstInst))
if (CmpInst *CIOp = dyn_cast<CmpInst>(FirstInst))
return CmpInst::Create(CIOp->getOpcode(), CIOp->getPredicate(), LHSVal,
RHSVal);
else {
assert(isa<GetElementPtrInst>(FirstInst));
return GetElementPtrInst::Create(LHSVal, RHSVal);
}
assert(isa<GetElementPtrInst>(FirstInst));
return GetElementPtrInst::Create(LHSVal, RHSVal);
}
Instruction *InstCombiner::FoldPHIArgGEPIntoPHI(PHINode &PN) {
GetElementPtrInst *FirstInst =cast<GetElementPtrInst>(PN.getIncomingValue(0));
SmallVector<Value*, 16> FixedOperands(FirstInst->op_begin(),
FirstInst->op_end());
// Scan to see if all operands are the same opcode, all have one use, and all
// kill their operands (i.e. the operands have one use).
for (unsigned i = 1; i != PN.getNumIncomingValues(); ++i) {
GetElementPtrInst *GEP= dyn_cast<GetElementPtrInst>(PN.getIncomingValue(i));
if (!GEP || !GEP->hasOneUse() || GEP->getType() != FirstInst->getType() ||
GEP->getNumOperands() != FirstInst->getNumOperands())
return 0;
// Compare the operand lists.
for (unsigned op = 0, e = FirstInst->getNumOperands(); op != e; ++op) {
if (FirstInst->getOperand(op) == GEP->getOperand(op))
continue;
// Don't merge two GEPs when two operands differ (introducing phi nodes)
// if one of the PHIs has a constant for the index. The index may be
// substantially cheaper to compute for the constants, so making it a
// variable index could pessimize the path. This also handles the case
// for struct indices, which must always be constant.
if (isa<ConstantInt>(FirstInst->getOperand(op)) ||
isa<ConstantInt>(GEP->getOperand(op)))
return 0;
if (FirstInst->getOperand(op)->getType() !=GEP->getOperand(op)->getType())
return 0;
FixedOperands[op] = 0; // Needs a PHI.
}
}
// Otherwise, this is safe to transform. Insert PHI nodes for each operand
// that is variable.
SmallVector<PHINode*, 16> OperandPhis(FixedOperands.size());
bool HasAnyPHIs = false;
for (unsigned i = 0, e = FixedOperands.size(); i != e; ++i) {
if (FixedOperands[i]) continue; // operand doesn't need a phi.
Value *FirstOp = FirstInst->getOperand(i);
PHINode *NewPN = PHINode::Create(FirstOp->getType(),
FirstOp->getName()+".pn");
InsertNewInstBefore(NewPN, PN);
NewPN->reserveOperandSpace(e);
NewPN->addIncoming(FirstOp, PN.getIncomingBlock(0));
OperandPhis[i] = NewPN;
FixedOperands[i] = NewPN;
HasAnyPHIs = true;
}
// Add all operands to the new PHIs.
if (HasAnyPHIs) {
for (unsigned i = 1, e = PN.getNumIncomingValues(); i != e; ++i) {
GetElementPtrInst *InGEP =cast<GetElementPtrInst>(PN.getIncomingValue(i));
BasicBlock *InBB = PN.getIncomingBlock(i);
for (unsigned op = 0, e = OperandPhis.size(); op != e; ++op)
if (PHINode *OpPhi = OperandPhis[op])
OpPhi->addIncoming(InGEP->getOperand(op), InBB);
}
}
Value *Base = FixedOperands[0];
return GetElementPtrInst::Create(Base, FixedOperands.begin()+1,
FixedOperands.end());
}
/// isSafeToSinkLoad - Return true if we know that it is safe sink the load out
/// of the block that defines it. This means that it must be obvious the value
/// of the load is not changed from the point of the load to the end of the
@ -10134,8 +10209,7 @@ Instruction *InstCombiner::FoldPHIArgOpIntoPHI(PHINode &PN) {
} else if (isa<GetElementPtrInst>(FirstInst)) {
if (FirstInst->getNumOperands() == 2)
return FoldPHIArgBinOpIntoPHI(PN);
// Can't handle general GEPs yet.
return 0;
return FoldPHIArgGEPIntoPHI(PN);
} else {
return 0; // Cannot fold this operation.
}
@ -10279,6 +10353,11 @@ Instruction *InstCombiner::visitPHINode(PHINode &PN) {
// If all PHI operands are the same operation, pull them through the PHI,
// reducing code size.
if (isa<Instruction>(PN.getIncomingValue(0)) &&
isa<Instruction>(PN.getIncomingValue(1)) &&
cast<Instruction>(PN.getIncomingValue(0))->getOpcode() ==
cast<Instruction>(PN.getIncomingValue(1))->getOpcode() &&
// FIXME: The hasOneUse check will fail for PHIs that use the value more
// than themselves more than once.
PN.getIncomingValue(0)->hasOneUse())
if (Instruction *Result = FoldPHIArgOpIntoPHI(PN))
return Result;

16
llvm/test/Transforms/InstCombine/phi.ll
View File

@ -1,7 +1,6 @@
; This test makes sure that these instructions are properly eliminated.
;
; RUN: llvm-as < %s | opt -instcombine | llvm-dis | not grep phi
; END.
define i32 @test1(i32 %A, i1 %b) {
BB0:
@ -98,4 +97,19 @@ Exit: ; preds = %Loop
ret i32 0
}
define i32* @test8({ i32, i32 } *%A, i1 %b) {
BB0:
%X = getelementptr { i32, i32 } *%A, i32 0, i32 1
br i1 %b, label %BB1, label %BB2
BB1:
%Y = getelementptr { i32, i32 } *%A, i32 0, i32 1
br label %BB2
BB2:
;; Suck GEPs into phi
%B = phi i32* [ %X, %BB0 ], [ %Y, %BB1 ]
ret i32* %B
}