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cc65/src/cc65/coptjmp.c

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/*****************************************************************************/
/* */
/* coptjmp.c */
/* */
/* Low level optimizations regarding branches and jumps */
/* */
/* */
/* */
/* (C) 2001-2009, Ullrich von Bassewitz */
/* Roemerstrasse 52 */
/* D-70794 Filderstadt */
/* EMail: uz@cc65.org */
/* */
/* */
/* This software is provided 'as-is', without any expressed or implied */
/* warranty. In no event will the authors be held liable for any damages */
/* arising from the use of this software. */
/* */
/* Permission is granted to anyone to use this software for any purpose, */
/* including commercial applications, and to alter it and redistribute it */
/* freely, subject to the following restrictions: */
/* */
/* 1. The origin of this software must not be misrepresented; you must not */
/* claim that you wrote the original software. If you use this software */
/* in a product, an acknowledgment in the product documentation would be */
/* appreciated but is not required. */
/* 2. Altered source versions must be plainly marked as such, and must not */
/* be misrepresented as being the original software. */
/* 3. This notice may not be removed or altered from any source */
/* distribution. */
/* */
/*****************************************************************************/
/* common */
#include "cpu.h"
/* cc65 */
#include "codeent.h"
#include "coptjmp.h"
#include "codeinfo.h"
#include "codeopt.h"
#include "error.h"
/*****************************************************************************/
/* Helper functions */
/*****************************************************************************/
static int GetBranchDist (CodeSeg* S, unsigned From, CodeEntry* To)
/* Get the branch distance between the two entries and return it. The distance
** will be negative for backward jumps and positive for forward jumps.
*/
{
/* Get the index of the branch target */
unsigned TI = CS_GetEntryIndex (S, To);
/* Determine the branch distance */
int Distance = 0;
if (TI >= From) {
/* Forward branch, do not count the current insn */
unsigned J = From+1;
while (J < TI) {
CodeEntry* N = CS_GetEntry (S, J++);
Distance += N->Size;
}
} else {
/* Backward branch */
unsigned J = TI;
while (J < From) {
CodeEntry* N = CS_GetEntry (S, J++);
Distance -= N->Size;
}
}
/* Return the calculated distance */
return Distance;
}
static int IsShortDist (int Distance)
/* Return true if the given distance is a short branch distance */
{
return (Distance >= -125 && Distance <= 125);
}
static short ZPRegVal (unsigned short Use, const RegContents* RC)
/* Return the contents of the given zeropage register */
{
if ((Use & REG_TMP1) != 0) {
return RC->Tmp1;
} else if ((Use & REG_PTR1_LO) != 0) {
return RC->Ptr1Lo;
} else if ((Use & REG_PTR1_HI) != 0) {
return RC->Ptr1Hi;
} else if ((Use & REG_SREG_LO) != 0) {
return RC->SRegLo;
} else if ((Use & REG_SREG_HI) != 0) {
return RC->SRegHi;
} else {
return UNKNOWN_REGVAL;
}
}
static short RegVal (unsigned short Use, const RegContents* RC)
/* Return the contents of the given register */
{
if ((Use & REG_A) != 0) {
return RC->RegA;
} else if ((Use & REG_X) != 0) {
return RC->RegX;
} else if ((Use & REG_Y) != 0) {
return RC->RegY;
} else {
return ZPRegVal (Use, RC);
}
}
/*****************************************************************************/
/* Optimize branch types */
/*****************************************************************************/
unsigned OptBranchDist (CodeSeg* S)
/* Change branches for the distance needed. */
{
unsigned Changes = 0;
/* Walk over the entries */
unsigned I = 0;
while (I < CS_GetEntryCount (S)) {
/* Get next entry */
CodeEntry* E = CS_GetEntry (S, I);
/* Check if it's a conditional branch to a local label. */
if (E->Info & OF_CBRA) {
/* Is this a branch to a local symbol? */
if (E->JumpTo != 0) {
/* Check if the branch distance is short */
int IsShort = IsShortDist (GetBranchDist (S, I, E->JumpTo->Owner));
/* Make the branch short/long according to distance */
if ((E->Info & OF_LBRA) == 0 && !IsShort) {
/* Short branch but long distance */
CE_ReplaceOPC (E, MakeLongBranch (E->OPC));
++Changes;
} else if ((E->Info & OF_LBRA) != 0 && IsShort) {
/* Long branch but short distance */
CE_ReplaceOPC (E, MakeShortBranch (E->OPC));
++Changes;
}
} else if ((E->Info & OF_LBRA) == 0) {
/* Short branch to external symbol - make it long */
CE_ReplaceOPC (E, MakeLongBranch (E->OPC));
++Changes;
}
} else if ((CPUIsets[CPU] & (CPU_ISET_65SC02 |CPU_ISET_6502DTV)) != 0 &&
(E->Info & OF_UBRA) != 0 &&
E->JumpTo != 0 &&
IsShortDist (GetBranchDist (S, I, E->JumpTo->Owner))) {
/* The jump is short and may be replaced by a BRA on the 65C02 CPU */
CE_ReplaceOPC (E, OP65_BRA);
++Changes;
}
/* Next entry */
++I;
}
/* Return the number of changes made */
return Changes;
}
unsigned OptBranchDist2 (CodeSeg* S)
/* Change BRA to JMP if target is an external symbol */
{
unsigned Changes = 0;
/* Walk over the entries */
unsigned I = 0;
while (I < CS_GetEntryCount (S)) {
/* Get next entry */
CodeEntry* E = CS_GetEntry (S, I);
if ((CPUIsets[CPU] & (CPU_ISET_65SC02 |CPU_ISET_6502DTV)) != 0 && /* CPU has BRA */
(E->Info & OF_UBRA) != 0 && /* is a unconditional branch */
E->JumpTo == NULL) { /* target is extern */
/* BRA jumps to external symbol and must be replaced by a JMP on the 65C02 CPU */
CE_ReplaceOPC (E, OP65_JMP);
++Changes;
}
/* Next entry */
++I;
}
/* Return the number of changes made */
return Changes;
}
/*****************************************************************************/
/* Replace jumps to RTS by RTS */
/*****************************************************************************/
unsigned OptRTSJumps1 (CodeSeg* S)
/* Replace jumps to RTS by RTS */
{
unsigned Changes = 0;
/* Walk over all entries minus the last one */
unsigned I = 0;
while (I < CS_GetEntryCount (S)) {
/* Get the next entry */
CodeEntry* E = CS_GetEntry (S, I);
/* Check if it's an unconditional branch to a local target */
if ((E->Info & OF_UBRA) != 0 &&
E->JumpTo != 0 &&
E->JumpTo->Owner->OPC == OP65_RTS) {
/* Insert an RTS instruction */
CodeEntry* X = NewCodeEntry (OP65_RTS, AM65_IMP, 0, 0, E->LI);
CS_InsertEntry (S, X, I+1);
/* Delete the jump */
CS_DelEntry (S, I);
/* Remember, we had changes */
++Changes;
}
/* Next entry */
++I;
}
/* Return the number of changes made */
return Changes;
}
unsigned OptRTSJumps2 (CodeSeg* S)
/* Replace long conditional jumps to RTS or to a final target */
{
unsigned Changes = 0;
/* Walk over all entries minus the last one */
unsigned I = 0;
while (I < CS_GetEntryCount (S) - 1) {
/* Get the next entry */
CodeEntry* E = CS_GetEntry (S, I);
/* Check if it's an conditional branch to a local target */
if ((E->Info & OF_CBRA) != 0 && /* Conditional branch */
(E->Info & OF_LBRA) != 0 && /* Long branch */
E->JumpTo != 0) { /* Local label */
/* Get the jump target and the next entry. There's always a next
** entry, because we don't cover the last entry in the loop.
*/
CodeEntry* X = 0;
CodeEntry* T = E->JumpTo->Owner;
CodeEntry* N = CS_GetNextEntry (S, I);
/* Check if it's a jump to an RTS insn */
if (T->OPC == OP65_RTS) {
/* It's a jump to RTS. Create a conditional branch around an
** RTS insn.
*/
X = NewCodeEntry (OP65_RTS, AM65_IMP, 0, 0, T->LI);
} else if (T->OPC == OP65_JMP && T->JumpTo == 0) {
/* It's a jump to a label outside the function. Create a
** conditional branch around a jump to the external label.
*/
X = NewCodeEntry (OP65_JMP, AM65_ABS, T->Arg, T->JumpTo, T->LI);
}
/* If we have a replacement insn, insert it */
if (X) {
CodeLabel* LN;
opc_t NewBranch;
/* Insert the new insn */
CS_InsertEntry (S, X, I+1);
/* Create a conditional branch with the inverse condition
** around the replacement insn
*/
/* Get the new branch opcode */
NewBranch = MakeShortBranch (GetInverseBranch (E->OPC));
/* Get the label attached to N, create a new one if needed */
LN = CS_GenLabel (S, N);
/* Generate the branch */
X = NewCodeEntry (NewBranch, AM65_BRA, LN->Name, LN, E->LI);
CS_InsertEntry (S, X, I+1);
/* Delete the long branch */
CS_DelEntry (S, I);
/* Remember, we had changes */
++Changes;
}
}
/* Next entry */
++I;
}
/* Return the number of changes made */
return Changes;
}
/*****************************************************************************/
/* Remove dead jumps */
/*****************************************************************************/
unsigned OptDeadJumps (CodeSeg* S)
/* Remove dead jumps (jumps to the next instruction) */
{
unsigned Changes = 0;
/* Walk over all entries minus the last one */
unsigned I = 0;
while (I < CS_GetEntryCount (S)) {
/* Get the next entry */
CodeEntry* E = CS_GetEntry (S, I);
/* Check if it's a branch, if it has a local target, and if the target
** is the next instruction.
*/
if (E->AM == AM65_BRA &&
E->JumpTo &&
E->JumpTo->Owner == CS_GetNextEntry (S, I)) {
/* Delete the dead jump */
CS_DelEntry (S, I);
/* Remember, we had changes */
++Changes;
} else {
/* Next entry */
++I;
}
}
/* Return the number of changes made */
return Changes;
}
/*****************************************************************************/
/* Remove dead code */
/*****************************************************************************/
unsigned OptDeadCode (CodeSeg* S)
/* Remove dead code (code that follows an unconditional jump or an rts/rti
** and has no label)
*/
{
unsigned Changes = 0;
/* Walk over all entries */
unsigned I = 0;
while (I < CS_GetEntryCount (S)) {
CodeEntry* N;
CodeLabel* LN;
/* Get this entry */
CodeEntry* E = CS_GetEntry (S, I);
/* Check if it's an unconditional branch, and if the next entry has
** no labels attached, or if the label is just used so that the insn
** can jump to itself.
*/
if ((E->Info & OF_DEAD) != 0 && /* Dead code follows */
(N = CS_GetNextEntry (S, I)) != 0 && /* Has next entry */
(!CE_HasLabel (N) || /* Don't has a label */
((N->Info & OF_UBRA) != 0 && /* Uncond branch */
(LN = N->JumpTo) != 0 && /* Jumps to known label */
LN->Owner == N && /* Attached to insn */
CL_GetRefCount (LN) == 1))) { /* Only reference */
/* Delete the next entry */
CS_DelEntry (S, I+1);
/* Remember, we had changes */
++Changes;
} else {
/* Next entry */
++I;
}
}
/* Return the number of changes made */
return Changes;
}
/*****************************************************************************/
/* Optimize jump cascades */
/*****************************************************************************/
unsigned OptJumpCascades (CodeSeg* S)
/* Optimize jump cascades (jumps to jumps). In such a case, the jump is
** replaced by a jump to the final location. This will in some cases produce
** worse code, because some jump targets are no longer reachable by short
** branches, but this is quite rare, so there are more advantages than
** disadvantages.
*/
{
unsigned Changes = 0;
/* Walk over all entries */
unsigned I = 0;
while (I < CS_GetEntryCount (S)) {
CodeEntry* N;
CodeLabel* OldLabel;
/* Get this entry */
CodeEntry* E = CS_GetEntry (S, I);
/* Check:
** - if it's a branch,
** - if it has a jump label,
** - if this jump label is not attached to the instruction itself,
** - if the target instruction is itself a branch,
** - if either the first branch is unconditional or the target of
** the second branch is internal to the function.
** The latter condition will avoid conditional branches to targets
** outside of the function (usually incspx), which won't simplify the
** code, since conditional far branches are emulated by a short branch
** around a jump.
*/
if ((E->Info & OF_BRA) != 0 &&
(OldLabel = E->JumpTo) != 0 &&
(N = OldLabel->Owner) != E &&
(N->Info & OF_BRA) != 0 &&
((E->Info & OF_CBRA) == 0 ||
N->JumpTo != 0)) {
/* Check if we can use the final target label. That is the case,
** if the target branch is an absolute branch; or, if it is a
** conditional branch checking the same condition as the first one.
*/
if ((N->Info & OF_UBRA) != 0 ||
((E->Info & OF_CBRA) != 0 &&
GetBranchCond (E->OPC) == GetBranchCond (N->OPC))) {
/* This is a jump cascade and we may jump to the final target,
** provided that the other insn does not jump to itself. If
** this is the case, we can also jump to ourselves, otherwise
** insert a jump to the new instruction and remove the old one.
*/
CodeEntry* X;
CodeLabel* LN = N->JumpTo;
if (LN != 0 && LN->Owner == N) {
/* We found a jump to a jump to itself. Replace our jump
** by a jump to itself.
*/
CodeLabel* LE = CS_GenLabel (S, E);
X = NewCodeEntry (E->OPC, E->AM, LE->Name, LE, E->LI);
} else {
/* Jump to the final jump target */
X = NewCodeEntry (E->OPC, E->AM, N->Arg, N->JumpTo, E->LI);
}
/* Insert it behind E */
CS_InsertEntry (S, X, I+1);
/* Remove E */
CS_DelEntry (S, I);
/* Remember, we had changes */
++Changes;
/* Check if both are conditional branches, and the condition of
** the second is the inverse of that of the first. In this case,
** the second branch will never be taken, and we may jump directly
** to the instruction behind this one.
*/
} else if ((E->Info & OF_CBRA) != 0 && (N->Info & OF_CBRA) != 0) {
CodeEntry* X; /* Instruction behind N */
CodeLabel* LX; /* Label attached to X */
/* Get the branch conditions of both branches */
bc_t BC1 = GetBranchCond (E->OPC);
bc_t BC2 = GetBranchCond (N->OPC);
/* Check the branch conditions */
if (BC1 != GetInverseCond (BC2)) {
/* Condition not met */
goto NextEntry;
}
/* We may jump behind this conditional branch. Get the
** pointer to the next instruction
*/
if ((X = CS_GetNextEntry (S, CS_GetEntryIndex (S, N))) == 0) {
/* N is the last entry, bail out */
goto NextEntry;
}
/* Get the label attached to X, create a new one if needed */
LX = CS_GenLabel (S, X);
/* Move the reference from E to the new label */
CS_MoveLabelRef (S, E, LX);
/* Remember, we had changes */
++Changes;
}
}
NextEntry:
/* Next entry */
++I;
}
/* Return the number of changes made */
return Changes;
}
/*****************************************************************************/
/* Optimize jsr/rts */
/*****************************************************************************/
unsigned OptRTS (CodeSeg* S)
/* Optimize subroutine calls followed by an RTS. The subroutine call will get
** replaced by a jump. Don't bother to delete the RTS if it does not have a
** label, the dead code elimination should take care of it.
*/
{
unsigned Changes = 0;
/* Walk over all entries minus the last one */
unsigned I = 0;
while (I < CS_GetEntryCount (S)) {
CodeEntry* N;
/* Get this entry */
CodeEntry* E = CS_GetEntry (S, I);
/* Check if it's a subroutine call and if the following insn is RTS */
if (E->OPC == OP65_JSR &&
(N = CS_GetNextEntry (S, I)) != 0 &&
N->OPC == OP65_RTS) {
/* Change the jsr to a jmp and use the additional info for a jump */
E->AM = AM65_BRA;
CE_ReplaceOPC (E, OP65_JMP);
/* Remember, we had changes */
++Changes;
}
/* Next entry */
++I;
}
/* Return the number of changes made */
return Changes;
}
/*****************************************************************************/
/* Optimize jump targets */
/*****************************************************************************/
unsigned OptJumpTarget1 (CodeSeg* S)
/* If the instruction preceeding an unconditional branch is the same as the
** instruction preceeding the jump target, the jump target may be moved
** one entry back. This is a size optimization, since the instruction before
** the branch gets removed.
*/
{
unsigned Changes = 0;
CodeEntry* E1; /* Entry 1 */
CodeEntry* E2; /* Entry 2 */
CodeEntry* T1; /* Jump target entry 1 */
CodeLabel* TL1; /* Target label 1 */
/* Walk over the entries */
unsigned I = 0;
while (I < CS_GetEntryCount (S)) {
/* Get next entry */
E2 = CS_GetNextEntry (S, I);
/* Check if we have a jump or branch without a label attached, and
** a jump target, which is not attached to the jump itself
*/
if (E2 != 0 &&
(E2->Info & OF_UBRA) != 0 &&
!CE_HasLabel (E2) &&
E2->JumpTo &&
E2->JumpTo->Owner != E2) {
/* Get the entry preceeding the branch target */
T1 = CS_GetPrevEntry (S, CS_GetEntryIndex (S, E2->JumpTo->Owner));
if (T1 == 0) {
/* There is no such entry */
goto NextEntry;
}
/* The entry preceeding the branch target may not be the branch
** insn.
*/
if (T1 == E2) {
goto NextEntry;
}
/* Get the entry preceeding the jump */
E1 = CS_GetEntry (S, I);
/* Check if both preceeding instructions are identical */
if (!CodeEntriesAreEqual (E1, T1)) {
/* Not equal, try next */
goto NextEntry;
}
/* Get the label for the instruction preceeding the jump target.
** This routine will create a new label if the instruction does
** not already have one.
*/
TL1 = CS_GenLabel (S, T1);
/* Change the jump target to point to this new label */
CS_MoveLabelRef (S, E2, TL1);
/* If the instruction preceeding the jump has labels attached,
** move references to this label to the new label.
*/
if (CE_HasLabel (E1)) {
CS_MoveLabels (S, E1, T1);
}
/* Remove the entry preceeding the jump */
CS_DelEntry (S, I);
/* Remember, we had changes */
++Changes;
} else {
NextEntry:
/* Next entry */
++I;
}
}
/* Return the number of changes made */
return Changes;
}
unsigned OptJumpTarget2 (CodeSeg* S)
/* If a bcs jumps to a sec insn or a bcc jumps to clc, skip this insn, since
** it's job is already done.
*/
{
unsigned Changes = 0;
/* Walk over the entries */
unsigned I = 0;
while (I < CS_GetEntryCount (S)) {
/* OP that may be skipped */
opc_t OPC;
/* Jump target insn, old and new */
CodeEntry* T;
CodeEntry* N;
/* New jump label */
CodeLabel* L;
/* Get next entry */
CodeEntry* E = CS_GetEntry (S, I);
/* Check if this is a bcc insn */
if (E->OPC == OP65_BCC || E->OPC == OP65_JCC) {
OPC = OP65_CLC;
} else if (E->OPC == OP65_BCS || E->OPC == OP65_JCS) {
OPC = OP65_SEC;
} else {
/* Not what we're looking for */
goto NextEntry;
}
/* Must have a jump target */
if (E->JumpTo == 0) {
goto NextEntry;
}
/* Get the owner insn of the jump target and check if it's the one, we
** will skip if present.
*/
T = E->JumpTo->Owner;
if (T->OPC != OPC) {
goto NextEntry;
}
/* Get the entry following the branch target */
N = CS_GetNextEntry (S, CS_GetEntryIndex (S, T));
if (N == 0) {
/* There is no such entry */
goto NextEntry;
}
/* Get the label for the instruction following the jump target.
** This routine will create a new label if the instruction does
** not already have one.
*/
L = CS_GenLabel (S, N);
/* Change the jump target to point to this new label */
CS_MoveLabelRef (S, E, L);
/* Remember that we had changes */
++Changes;
NextEntry:
/* Next entry */
++I;
}
/* Return the number of changes made */
return Changes;
}
unsigned OptJumpTarget3 (CodeSeg* S)
/* Jumps to load instructions of a register, that do already have the matching
** register contents may skip the load instruction, since it's job is already
** done.
*/
{
unsigned Changes = 0;
unsigned I;
/* Walk over the entries */
I = 0;
while (I < CS_GetEntryCount (S)) {
CodeEntry* N;
/* Get next entry */
CodeEntry* E = CS_GetEntry (S, I);
/* Check if this is a load insn with a label and the next insn is not
** a conditional branch that needs the flags from the load.
*/
if ((E->Info & OF_LOAD) != 0 &&
CE_IsConstImm (E) &&
CE_HasLabel (E) &&
(N = CS_GetNextEntry (S, I)) != 0 &&
!CE_UseLoadFlags (N)) {
unsigned J;
int K;
/* New jump label */
CodeLabel* LN = 0;
/* Walk over all insn that jump here */
for (J = 0; J < CE_GetLabelCount (E); ++J) {
/* Get the label */
CodeLabel* L = CE_GetLabel (E, J);
/* Loop over all insn that reference this label. Since we may
** eventually remove a reference in the loop, we must loop
** from end down to start.
*/
for (K = CL_GetRefCount (L) - 1; K >= 0; --K) {
/* Get the entry that jumps here */
CodeEntry* Jump = CL_GetRef (L, K);
/* Get the register info from this insn */
short Val = RegVal (E->Chg, &Jump->RI->Out2);
/* Check if the outgoing value is the one thats's loaded */
if (Val == (unsigned char) E->Num) {
/* OK, skip the insn. First, generate a label for the
** next insn after E.
*/
if (LN == 0) {
LN = CS_GenLabel (S, N);
}
/* Change the jump target to point to this new label */
CS_MoveLabelRef (S, Jump, LN);
/* Remember that we had changes */
++Changes;
}
}
}
}
/* Next entry */
++I;
}
/* Return the number of changes made */
return Changes;
}
/*****************************************************************************/
/* Optimize conditional branches */
/*****************************************************************************/
unsigned OptCondBranch1 (CodeSeg* S)
/* Performs some optimization steps:
** - If an immediate load of a register is followed by a conditional jump that
** is never taken because the load of the register sets the flags in such a
** manner, remove the conditional branch.
** - If the conditional branch is always taken because of the register load,
** replace it by a jmp.
*/
{
unsigned Changes = 0;
/* Walk over the entries */
unsigned I = 0;
while (I < CS_GetEntryCount (S)) {
CodeEntry* N;
/* Get next entry */
CodeEntry* E = CS_GetEntry (S, I);
/* Check if it's a register load */
if ((E->Info & OF_LOAD) != 0 && /* It's a load instruction */
E->AM == AM65_IMM && /* ..with immidiate addressing */
CE_HasNumArg (E) && /* ..and a numeric argument. */
(N = CS_GetNextEntry (S, I)) != 0 && /* There is a following entry */
(N->Info & OF_CBRA) != 0 && /* ..which is a conditional branch */
!CE_HasLabel (N)) { /* ..and does not have a label */
/* Get the branch condition */
bc_t BC = GetBranchCond (N->OPC);
/* Check the argument against the branch condition */
if ((BC == BC_EQ && E->Num != 0) ||
(BC == BC_NE && E->Num == 0) ||
(BC == BC_PL && (E->Num & 0x80) != 0) ||
(BC == BC_MI && (E->Num & 0x80) == 0)) {
/* Remove the conditional branch */
CS_DelEntry (S, I+1);
/* Remember, we had changes */
++Changes;
} else if ((BC == BC_EQ && E->Num == 0) ||
(BC == BC_NE && E->Num != 0) ||
(BC == BC_PL && (E->Num & 0x80) == 0) ||
(BC == BC_MI && (E->Num & 0x80) != 0)) {
/* The branch is always taken, replace it by a jump */
CE_ReplaceOPC (N, OP65_JMP);
/* Remember, we had changes */
++Changes;
}
}
/* Next entry */
++I;
}
/* Return the number of changes made */
return Changes;
}
unsigned OptCondBranch2 (CodeSeg* S)
/* If a conditional branch jumps around an unconditional branch, remove the
** conditional branch and make the jump a conditional branch with the inverse
** condition of the first one.
*/
{
unsigned Changes = 0;
/* Walk over the entries */
unsigned I = 0;
while (I < CS_GetEntryCount (S)) {
CodeEntry* N;
CodeLabel* L;
/* Get next entry */
CodeEntry* E = CS_GetEntry (S, I);
if ((E->Info & OF_CBRA) != 0 && /* It's a conditional branch */
(L = E->JumpTo) != 0 && /* ..referencing a local label */
(N = CS_GetNextEntry (S, I)) != 0 && /* There is a following entry */
(N->Info & OF_UBRA) != 0 && /* ..which is an uncond branch, */
!CE_HasLabel (N) && /* ..has no label attached */
L->Owner == CS_GetNextEntry (S, I+1)) { /* ..and jump target follows */
/* Replace the jump by a conditional branch with the inverse branch
** condition than the branch around it.
*/
CE_ReplaceOPC (N, GetInverseBranch (E->OPC));
/* Remove the conditional branch */
CS_DelEntry (S, I);
/* Remember, we had changes */
++Changes;
}
/* Next entry */
++I;
}
/* Return the number of changes made */
return Changes;
}
unsigned OptCondBranch3 (CodeSeg* S)
/* If the conditional branch is always taken because it follows an inverse
** conditional branch, replace it by a jmp.
*/
{
unsigned Changes = 0;
/* Walk over the entries */
unsigned I = 0;
while (I < CS_GetEntryCount (S)) {
CodeEntry* N;
/* Get next entry */
CodeEntry* E = CS_GetEntry (S, I);
/* Check if it's a conditional branch */
if ((E->Info & OF_CBRA) != 0 && /* It's a conditional branch */
(N = CS_GetNextEntry (S, I)) != 0 && /* There is a following entry */
(N->Info & OF_CBRA) != 0 && /* ..which is a conditional branch */
!CE_HasLabel (N)) { /* ..and does not have a label */
/* Check if the branches conditions are inverse of each other */
if (GetInverseCond (GetBranchCond (N->OPC)) == GetBranchCond (E->OPC)) {
/* The branch is always taken, replace it by a jump */
CE_ReplaceOPC (N, OP65_JMP);
/* Remember, we had changes */
++Changes;
}
}
/* Next entry */
++I;
}
/* Return the number of changes made */
return Changes;
}
unsigned OptCondBranchC (CodeSeg* S)
/* If on entry to a "rol a" instruction the accu is zero, and a beq/bne follows,
** we can remove the rol and branch on the state of the carry flag.
*/
{
unsigned Changes = 0;
unsigned I;
/* Walk over the entries */
I = 0;
while (I < CS_GetEntryCount (S)) {
CodeEntry* N;
/* Get next entry */
CodeEntry* E = CS_GetEntry (S, I);
/* Check if it's a rol insn with A in accu and a branch follows */
if (E->OPC == OP65_ROL &&
E->AM == AM65_ACC &&
E->RI->In.RegA == 0 &&
!CE_HasLabel (E) &&
(N = CS_GetNextEntry (S, I)) != 0 &&
(N->Info & OF_ZBRA) != 0 &&
!RegAUsed (S, I+1)) {
/* Replace the branch condition */
switch (GetBranchCond (N->OPC)) {
case BC_EQ: CE_ReplaceOPC (N, OP65_JCC); break;
case BC_NE: CE_ReplaceOPC (N, OP65_JCS); break;
default: Internal ("Unknown branch condition in OptCondBranches2");
}
/* Delete the rol insn */
CS_DelEntry (S, I);
/* Remember, we had changes */
++Changes;
}
/* Next entry */
++I;
}
/* Return the number of changes made */
return Changes;
}
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