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author | Evan Cheng <evan.cheng@apple.com> | 2008-11-27 00:49:46 +0000 |
---|---|---|
committer | Evan Cheng <evan.cheng@apple.com> | 2008-11-27 00:49:46 +0000 |
commit | 884c70c912b699a4d14d05dcac1ac4f2d47c0f9a (patch) | |
tree | eea845867e8c466b91a3bf184a9c9c1df7049e2e /lib | |
parent | 56eca9103ecbf2293842bfd6067ac26629221eaf (diff) | |
download | external_llvm-884c70c912b699a4d14d05dcac1ac4f2d47c0f9a.zip external_llvm-884c70c912b699a4d14d05dcac1ac4f2d47c0f9a.tar.gz external_llvm-884c70c912b699a4d14d05dcac1ac4f2d47c0f9a.tar.bz2 |
On x86 favors folding short immediate into some arithmetic operations (e.g. add, and, xor, etc.) because materializing an immediate in a register is expensive in turns of code size.
e.g.
movl 4(%esp), %eax
addl $4, %eax
is 2 bytes shorter than
movl $4, %eax
addl 4(%esp), %eax
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@60139 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib')
-rw-r--r-- | lib/Target/X86/X86ISelDAGToDAG.cpp | 45 |
1 files changed, 40 insertions, 5 deletions
diff --git a/lib/Target/X86/X86ISelDAGToDAG.cpp b/lib/Target/X86/X86ISelDAGToDAG.cpp index 4bb9c23..e6c3448 100644 --- a/lib/Target/X86/X86ISelDAGToDAG.cpp +++ b/lib/Target/X86/X86ISelDAGToDAG.cpp @@ -141,7 +141,8 @@ namespace { virtual void EmitFunctionEntryCode(Function &Fn, MachineFunction &MF); - virtual bool CanBeFoldedBy(SDNode *N, SDNode *U, SDNode *Root) const; + virtual + bool IsLegalAndProfitableToFold(SDNode *N, SDNode *U, SDNode *Root) const; // Include the pieces autogenerated from the target description. #include "X86GenDAGISel.inc" @@ -280,7 +281,8 @@ static void findNonImmUse(SDNode *Use, SDNode* Def, SDNode *ImmedUse, /// isNonImmUse - Start searching from Root up the DAG to check is Def can /// be reached. Return true if that's the case. However, ignore direct uses /// by ImmedUse (which would be U in the example illustrated in -/// CanBeFoldedBy) and by Root (which can happen in the store case). +/// IsLegalAndProfitableToFold) and by Root (which can happen in the store +/// case). /// FIXME: to be really generic, we should allow direct use by any node /// that is being folded. But realisticly since we only fold loads which /// have one non-chain use, we only need to watch out for load/op/store @@ -294,9 +296,42 @@ static inline bool isNonImmUse(SDNode *Root, SDNode *Def, SDNode *ImmedUse) { } -bool X86DAGToDAGISel::CanBeFoldedBy(SDNode *N, SDNode *U, SDNode *Root) const { +bool X86DAGToDAGISel::IsLegalAndProfitableToFold(SDNode *N, SDNode *U, + SDNode *Root) const { if (Fast) return false; + if (U == Root) + switch (U->getOpcode()) { + default: break; + case ISD::ADD: + case ISD::ADDC: + case ISD::ADDE: + case ISD::AND: + case ISD::OR: + case ISD::XOR: { + // If the other operand is a 8-bit immediate we should fold the immediate + // instead. This reduces code size. + // e.g. + // movl 4(%esp), %eax + // addl $4, %eax + // vs. + // movl $4, %eax + // addl 4(%esp), %eax + // The former is 2 bytes shorter. In case where the increment is 1, then + // the saving can be 4 bytes (by using incl %eax). + ConstantSDNode *Imm = dyn_cast<ConstantSDNode>(U->getOperand(1)); + if (Imm) { + if (U->getValueType(0) == MVT::i64) { + if ((int32_t)Imm->getZExtValue() == (int64_t)Imm->getZExtValue()) + return false; + } else { + if ((int8_t)Imm->getZExtValue() == (int64_t)Imm->getZExtValue()) + return false; + } + } + } + } + // If Root use can somehow reach N through a path that that doesn't contain // U then folding N would create a cycle. e.g. In the following // diagram, Root can reach N through X. If N is folded into into Root, then @@ -999,7 +1034,7 @@ bool X86DAGToDAGISel::SelectScalarSSELoad(SDValue Op, SDValue Pred, if (ISD::isNON_EXTLoad(InChain.getNode()) && InChain.getValue(0).hasOneUse() && N.hasOneUse() && - CanBeFoldedBy(N.getNode(), Pred.getNode(), Op.getNode())) { + IsLegalAndProfitableToFold(N.getNode(), Pred.getNode(), Op.getNode())) { LoadSDNode *LD = cast<LoadSDNode>(InChain); if (!SelectAddr(Op, LD->getBasePtr(), Base, Scale, Index, Disp)) return false; @@ -1086,7 +1121,7 @@ bool X86DAGToDAGISel::TryFoldLoad(SDValue P, SDValue N, SDValue &Index, SDValue &Disp) { if (ISD::isNON_EXTLoad(N.getNode()) && N.hasOneUse() && - CanBeFoldedBy(N.getNode(), P.getNode(), P.getNode())) + IsLegalAndProfitableToFold(N.getNode(), P.getNode(), P.getNode())) return SelectAddr(P, N.getOperand(1), Base, Scale, Index, Disp); return false; } |