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Basic "in frame" alias analysis. 

llvm-svn: 30568
This commit is contained in:
Jim Laskey 2006-09-21 16:28:59 +00:00
parent 7b700e517a
commit 5d19d59017
1 changed files with 49 additions and 1 deletions
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50
llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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@ -35,6 +35,7 @@
#include "llvm/Support/MathExtras.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/CommandLine.h"
#include <algorithm>
#include <cmath>
#include <iostream>
@ -43,8 +44,17 @@ using namespace llvm;
namespace {
static Statistic<> NodesCombined ("dagcombiner",
"Number of dag nodes combined");
class VISIBILITY_HIDDEN DAGCombiner {
#ifndef NDEBUG
static cl::opt<bool>
CombinerAA("combiner-alias-analysis", cl::Hidden,
cl::desc("Turn on alias analysis turning testing"));
#else
static const bool CombinerAA = 0;
#endif
class VISIBILITY_HIDDEN DAGCombiner {
SelectionDAG &DAG;
TargetLowering &TLI;
bool AfterLegalize;
@ -231,6 +241,7 @@ namespace {
SDOperand BuildSDIV(SDNode *N);
SDOperand BuildUDIV(SDNode *N);
SDNode *MatchRotate(SDOperand LHS, SDOperand RHS);
bool isNotAlias(SDOperand Ptr1, SDOperand Ptr2);
public:
DAGCombiner(SelectionDAG &D)
: DAG(D), TLI(D.getTargetLoweringInfo()), AfterLegalize(false) {}
@ -2577,6 +2588,27 @@ SDOperand DAGCombiner::visitXEXTLOAD(SDNode *N) {
return SDOperand();
}
/// isNotAlias - Return true if we have definitive knowlege that the two
/// addresses don't overlap.
bool DAGCombiner::isNotAlias(SDOperand Ptr1, SDOperand Ptr2) {
// Mind the flag.
if (!CombinerAA) return false;
// If they are the same then they are simple aliases.
if (Ptr1 == Ptr2) return false;
// If either operand is a frame value (not the same location from above test)
// then they can't alias.
FrameIndexSDNode *FI1 = dyn_cast<FrameIndexSDNode>(Ptr1);
FrameIndexSDNode *FI2 = dyn_cast<FrameIndexSDNode>(Ptr2);
if (FI1 || FI2) {
return true;
}
// Otherwise we don't know and have to play it safe.
return false;
}
SDOperand DAGCombiner::visitSTORE(SDNode *N) {
SDOperand Chain = N->getOperand(0);
SDOperand Value = N->getOperand(1);
@ -2607,6 +2639,22 @@ SDOperand DAGCombiner::visitSTORE(SDNode *N) {
if (0 && Value.getOpcode() == ISD::BIT_CONVERT)
return DAG.getNode(ISD::STORE, MVT::Other, Chain, Value.getOperand(0),
Ptr, SrcValue);
// If the previous store is not an alias then break artificial chain.
if (Chain.getOpcode() == ISD::STORE && isNotAlias(Ptr, Chain.getOperand(2))) {
// Replace the chain to void dependency.
SDNode *PrevStore = Chain.Val;
SDOperand ReplStore = DAG.getNode(ISD::STORE, MVT::Other,
PrevStore->getOperand(0), Value, Ptr,
SrcValue);
// Create token to keep both stores around.
SDOperand Token = DAG.getNode(ISD::TokenFactor, MVT::Other,
Chain, ReplStore);
// Replace uses with token.
CombineTo(N, Token);
// Don't recombine on token.
return SDOperand(N, 0);
}
return SDOperand();
}