From 2db04f4efc7f0866906015d08b70855687878b7a Mon Sep 17 00:00:00 2001
From: clc5q <clc5q@git.zephyr-software.com>
Date: Sat, 17 May 2008 03:12:12 +0000
Subject: [PATCH] Treat xor reg,reg as mov reg,0.
---
SMPInstr.cpp | 61 ++++++++++++++++++++++++++++++++++++++++------------
SMPInstr.h | 7 ++++--
2 files changed, 52 insertions(+), 16 deletions(-)
diff --git a/SMPInstr.cpp b/SMPInstr.cpp
index 6085406d..64bed3c2 100644
--- a/SMPInstr.cpp
+++ b/SMPInstr.cpp
@@ -198,6 +198,7 @@ SMPInstr::SMPInstr(ea_t addr) {
this->BlockTerm = false;
this->TailCall = false;
this->Interrupt = false;
+ this->RegClearIdiom = false;
this->DeadRegsString[0] = '\0';
this->DefsFlags = false;
this->UsesFlags = false;
@@ -710,6 +711,16 @@ void SMPInstr::Analyze(void) {
this->Interrupt = ((NN_int == cmd.itype) || (NN_into == cmd.itype) || (NN_int3 == cmd.itype));
+ // See if instruction is an ASM idiom for clearing a register.
+ if (NN_xor == this->SMPcmd.itype) {
+ ushort FirstReg;
+ if (o_reg == this->SMPcmd.Operands[0].type) {
+ FirstReg = this->SMPcmd.Operands[0].reg;
+ if (this->SMPcmd.Operands[1].is_reg(FirstReg))
+ this->RegClearIdiom = true;
+ }
+ }
+
// Build the DEF and USE lists for the instruction.
this->BuildSMPDefUseLists();
// Fix up machine dependent quirks in the def and use lists.
@@ -781,6 +792,19 @@ void SMPInstr::BuildSMPDefUseLists(void) {
}
} // end for (OpNum = 0; ...)
+ if (this->RegClearIdiom) {
+ // Something like xor eax,eax clears eax but does not really
+ // use eax. It is the same as mov eax,0 and we don't want to
+ // extend the prior def-use chain for eax to this instruction
+ // by treating the instruction as xor eax,eax. Instead, we
+ // build the DEF and USE lists and RTL as if it were mov eax,0.
+ op_t ImmOp;
+ ImmOp.type = o_imm;
+ ImmOp.value = 0;
+ this->Uses.SetRef(ImmOp, NUMERIC);
+ return;
+ }
+
// Now, do the Uses. Uses have special case operations, because
// any memory operand could have register uses in the addressing
// expression, and we must create Uses for those registers. For
@@ -816,7 +840,7 @@ void SMPInstr::BuildSMPDefUseLists(void) {
} // end of SMPInstr::BuildSMPDefUseLists()
// If DefReg is not already in the DEF list, add a DEF for it.
-void SMPInstr::MDAddRegDef(ushort DefReg, bool Shown) {
+void SMPInstr::MDAddRegDef(ushort DefReg, bool Shown, SMPOperandType Type) {
op_t TempDef;
TempDef.type = o_reg;
TempDef.reg = DefReg;
@@ -824,12 +848,12 @@ void SMPInstr::MDAddRegDef(ushort DefReg, bool Shown) {
TempDef.set_showed();
else
TempDef.clr_showed();
- this->Defs.SetRef(TempDef);
+ this->Defs.SetRef(TempDef, Type);
return;
} // end of SMPInstr::MDAddRegDef()
// If UseReg is not already in the USE list, add a USE for it.
-void SMPInstr::MDAddRegUse(ushort UseReg, bool Shown) {
+void SMPInstr::MDAddRegUse(ushort UseReg, bool Shown, SMPOperandType Type) {
op_t TempUse;
TempUse.type = o_reg;
TempUse.reg = UseReg;
@@ -837,7 +861,7 @@ void SMPInstr::MDAddRegUse(ushort UseReg, bool Shown) {
TempUse.set_showed();
else
TempUse.clr_showed();
- this->Uses.SetRef(TempUse);
+ this->Uses.SetRef(TempUse, Type);
return;
} // end of SMPInstr::MDAddRegUse()
@@ -948,8 +972,8 @@ void SMPInstr::MDFixupDefUseLists(void) {
BaseOpnd.reg = R_cx;
BaseOpnd.hasSIB = 0;
BaseOpnd.clr_showed();
- this->Defs.SetRef(BaseOpnd);
- this->Uses.SetRef(BaseOpnd);
+ this->Defs.SetRef(BaseOpnd, NUMERIC);
+ this->Uses.SetRef(BaseOpnd, NUMERIC);
}
if ((this->SMPcmd.itype == NN_cmps) || (this->SMPcmd.itype == NN_scas)
|| (this->SMPcmd.itype == NN_movs) || (this->SMPcmd.itype == NN_stos)) {
@@ -961,12 +985,12 @@ void SMPInstr::MDFixupDefUseLists(void) {
BaseOpnd.clr_showed();
if ((this->SMPcmd.itype == NN_cmps) || (this->SMPcmd.itype == NN_movs)) {
BaseOpnd.reg = R_si;
- this->Defs.SetRef(BaseOpnd);
- this->Uses.SetRef(BaseOpnd);
+ this->Defs.SetRef(BaseOpnd, POINTER);
+ this->Uses.SetRef(BaseOpnd, POINTER);
}
BaseOpnd.reg = R_di;
- this->Defs.SetRef(BaseOpnd);
- this->Uses.SetRef(BaseOpnd);
+ this->Defs.SetRef(BaseOpnd, POINTER);
+ this->Uses.SetRef(BaseOpnd, POINTER);
}
// Now, handle special instruction categories that have implicit operands.
@@ -1017,7 +1041,7 @@ void SMPInstr::MDFixupDefUseLists(void) {
this->MDAddRegUse(R_bp, false);
}
else if (this->SMPcmd.itype == NN_maskmovq) {
- this->MDAddRegUse(R_di, false);
+ this->MDAddRegUse(R_di, false, POINTER);
}
else if (8 == this->GetOptType()) {
// This category implicitly writes to EDX:EAX.
@@ -2753,9 +2777,18 @@ bool SMPInstr::BuildBinaryRTL(SMPoperator BinaryOp) {
TempRT = new SMPRegTransfer;
TempRT->SetLeftOperand(TempOp);
TempRT->SetOperator(SMP_ASSIGN);
- RightRT->SetLeftOperand(TempOp);
- RightRT->SetOperator(BinaryOp);
- TempRT->SetRightTree(RightRT);
+ if (this->RegClearIdiom) {
+ op_t ImmOp;
+ ImmOp.type = o_imm;
+ ImmOp.value = 0;
+ TempRT->SetRightOperand(ImmOp);
+ SourceFound = true; // cause loop exit
+ }
+ else {
+ RightRT->SetLeftOperand(TempOp);
+ RightRT->SetOperator(BinaryOp);
+ TempRT->SetRightTree(RightRT);
+ }
}
else {
;
diff --git a/SMPInstr.h b/SMPInstr.h
index ab661a2f..63e213ba 100644
--- a/SMPInstr.h
+++ b/SMPInstr.h
@@ -250,6 +250,7 @@ private:
bool TailCall; // This instruction is a tail call (jump to far chunk with stack restored).
bool CondTailCall; // Tail call is conditional branch.
bool Interrupt; // Instruction is a software interrupt call.
+ bool RegClearIdiom; // ASM idiom for move zero into register?
char DeadRegsString[MAXSTR]; // Registers that are dead at this instruction
bool DefsFlags; // Instr DEFs the flags
bool UsesFlags; // Instr USEs the flags
@@ -264,8 +265,10 @@ private:
bool AllDefsNumeric(void); // true if all DEFs are NUMERIC or CODEPTR
void BuildSMPDefUseLists(void); // Build DEF and USE lists for instruction
void MDFixupDefUseLists(void); // Machine-dependent ad hoc fixes
- void MDAddRegDef(ushort, bool); // Add DEF of register if not already a DEF
- void MDAddRegUse(ushort, bool); // Add USE of register if not already a USE
+ void MDAddRegDef(ushort DefReg, bool Shown, SMPOperandType Type = UNINIT);
+ // Add DEF of register if not already a DEF
+ void MDAddRegUse(ushort UseReg, bool Shown, SMPOperandType Type = UNINIT);
+ // Add USE of register if not already a USE
void MDAnnotateSIBStackConstants(FILE *, op_t, ea_t, bool); // Handle x86 opcode SIB byte
bool MDFindPointerUse(op_t MemOp, bool UseFP); // Set base reg to POINTER
op_t MDGetMemUseOp(void);
--
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