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Generate better code for multiplies by negative constants like -4, -1, -9, etc.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@15012 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2004-07-19 23:47:21 +00:00
parent da77c44c2c
commit 596b97f1ab
2 changed files with 84 additions and 8 deletions
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46
lib/Target/X86/InstSelectSimple.cpp
View File

@ -2324,11 +2324,21 @@ void ISel::doMultiplyConst(MachineBasicBlock *MBB,
static const unsigned MOVrrTab[] = {X86::MOV8rr, X86::MOV16rr, X86::MOV32rr};
static const unsigned MOVriTab[] = {X86::MOV8ri, X86::MOV16ri, X86::MOV32ri};
static const unsigned ADDrrTab[] = {X86::ADD8rr, X86::ADD16rr, X86::ADD32rr};
static const unsigned NEGrTab[] = {X86::NEG8r , X86::NEG16r , X86::NEG32r };
unsigned Class = getClass(DestTy);
unsigned TmpReg;
// Handle special cases here.
switch (ConstRHS) {
case -2:
TmpReg = makeAnotherReg(DestTy);
BuildMI(*MBB, IP, NEGrTab[Class], 1, TmpReg).addReg(op0Reg);
BuildMI(*MBB, IP, ADDrrTab[Class], 1,DestReg).addReg(TmpReg).addReg(TmpReg);
return;
case -1:
BuildMI(*MBB, IP, NEGrTab[Class], 1, DestReg).addReg(op0Reg);
return;
case 0:
BuildMI(*MBB, IP, MOVriTab[Class], 1, DestReg).addImm(0);
return;
@ -2342,10 +2352,20 @@ void ISel::doMultiplyConst(MachineBasicBlock *MBB,
case 5:
case 9:
if (Class == cInt) {
addFullAddress(BuildMI(*MBB, IP, X86::LEA32r, 5, DestReg),
addFullAddress(BuildMI(*MBB, IP, X86::LEA32r, 5, TmpReg),
op0Reg, ConstRHS-1, op0Reg, 0);
return;
}
case -3:
case -5:
case -9:
if (Class == cInt) {
TmpReg = makeAnotherReg(DestTy);
addFullAddress(BuildMI(*MBB, IP, X86::LEA32r, 5, TmpReg),
op0Reg, -ConstRHS-1, op0Reg, 0);
BuildMI(*MBB, IP, NEGrTab[Class], 1, DestReg).addReg(TmpReg);
return;
}
}
// If the element size is exactly a power of 2, use a shift to get it.
@ -2353,16 +2373,34 @@ void ISel::doMultiplyConst(MachineBasicBlock *MBB,
switch (Class) {
default: assert(0 && "Unknown class for this function!");
case cByte:
BuildMI(*MBB, IP, X86::SHL32ri,2, DestReg).addReg(op0Reg).addImm(Shift-1);
BuildMI(*MBB, IP, X86::SHL8ri,2, DestReg).addReg(op0Reg).addImm(Shift-1);
return;
case cShort:
BuildMI(*MBB, IP, X86::SHL32ri,2, DestReg).addReg(op0Reg).addImm(Shift-1);
BuildMI(*MBB, IP, X86::SHL16ri,2, DestReg).addReg(op0Reg).addImm(Shift-1);
return;
case cInt:
BuildMI(*MBB, IP, X86::SHL32ri,2, DestReg).addReg(op0Reg).addImm(Shift-1);
return;
}
}
// If the element size is a negative power of 2, use a shift/neg to get it.
if (unsigned Shift = ExactLog2(-ConstRHS)) {
TmpReg = makeAnotherReg(DestTy);
BuildMI(*MBB, IP, NEGrTab[Class], 1, TmpReg).addReg(op0Reg);
switch (Class) {
default: assert(0 && "Unknown class for this function!");
case cByte:
BuildMI(*MBB, IP, X86::SHL8ri,2, DestReg).addReg(TmpReg).addImm(Shift-1);
return;
case cShort:
BuildMI(*MBB, IP, X86::SHL16ri,2, DestReg).addReg(TmpReg).addImm(Shift-1);
return;
case cInt:
BuildMI(*MBB, IP, X86::SHL32ri,2, DestReg).addReg(TmpReg).addImm(Shift-1);
return;
}
}
if (Class == cShort) {
BuildMI(*MBB, IP, X86::IMUL16rri,2,DestReg).addReg(op0Reg).addImm(ConstRHS);
@ -2373,7 +2411,7 @@ void ISel::doMultiplyConst(MachineBasicBlock *MBB,
}
// Most general case, emit a normal multiply...
unsigned TmpReg = makeAnotherReg(DestTy);
TmpReg = makeAnotherReg(DestTy);
BuildMI(*MBB, IP, MOVriTab[Class], 1, TmpReg).addImm(ConstRHS);
// Emit a MUL to multiply the register holding the index by

46
lib/Target/X86/X86ISelSimple.cpp
View File

@ -2324,11 +2324,21 @@ void ISel::doMultiplyConst(MachineBasicBlock *MBB,
static const unsigned MOVrrTab[] = {X86::MOV8rr, X86::MOV16rr, X86::MOV32rr};
static const unsigned MOVriTab[] = {X86::MOV8ri, X86::MOV16ri, X86::MOV32ri};
static const unsigned ADDrrTab[] = {X86::ADD8rr, X86::ADD16rr, X86::ADD32rr};
static const unsigned NEGrTab[] = {X86::NEG8r , X86::NEG16r , X86::NEG32r };
unsigned Class = getClass(DestTy);
unsigned TmpReg;
// Handle special cases here.
switch (ConstRHS) {
case -2:
TmpReg = makeAnotherReg(DestTy);
BuildMI(*MBB, IP, NEGrTab[Class], 1, TmpReg).addReg(op0Reg);
BuildMI(*MBB, IP, ADDrrTab[Class], 1,DestReg).addReg(TmpReg).addReg(TmpReg);
return;
case -1:
BuildMI(*MBB, IP, NEGrTab[Class], 1, DestReg).addReg(op0Reg);
return;
case 0:
BuildMI(*MBB, IP, MOVriTab[Class], 1, DestReg).addImm(0);
return;
@ -2342,10 +2352,20 @@ void ISel::doMultiplyConst(MachineBasicBlock *MBB,
case 5:
case 9:
if (Class == cInt) {
addFullAddress(BuildMI(*MBB, IP, X86::LEA32r, 5, DestReg),
addFullAddress(BuildMI(*MBB, IP, X86::LEA32r, 5, TmpReg),
op0Reg, ConstRHS-1, op0Reg, 0);
return;
}
case -3:
case -5:
case -9:
if (Class == cInt) {
TmpReg = makeAnotherReg(DestTy);
addFullAddress(BuildMI(*MBB, IP, X86::LEA32r, 5, TmpReg),
op0Reg, -ConstRHS-1, op0Reg, 0);
BuildMI(*MBB, IP, NEGrTab[Class], 1, DestReg).addReg(TmpReg);
return;
}
}
// If the element size is exactly a power of 2, use a shift to get it.
@ -2353,16 +2373,34 @@ void ISel::doMultiplyConst(MachineBasicBlock *MBB,
switch (Class) {
default: assert(0 && "Unknown class for this function!");
case cByte:
BuildMI(*MBB, IP, X86::SHL32ri,2, DestReg).addReg(op0Reg).addImm(Shift-1);
BuildMI(*MBB, IP, X86::SHL8ri,2, DestReg).addReg(op0Reg).addImm(Shift-1);
return;
case cShort:
BuildMI(*MBB, IP, X86::SHL32ri,2, DestReg).addReg(op0Reg).addImm(Shift-1);
BuildMI(*MBB, IP, X86::SHL16ri,2, DestReg).addReg(op0Reg).addImm(Shift-1);
return;
case cInt:
BuildMI(*MBB, IP, X86::SHL32ri,2, DestReg).addReg(op0Reg).addImm(Shift-1);
return;
}
}
// If the element size is a negative power of 2, use a shift/neg to get it.
if (unsigned Shift = ExactLog2(-ConstRHS)) {
TmpReg = makeAnotherReg(DestTy);
BuildMI(*MBB, IP, NEGrTab[Class], 1, TmpReg).addReg(op0Reg);
switch (Class) {
default: assert(0 && "Unknown class for this function!");
case cByte:
BuildMI(*MBB, IP, X86::SHL8ri,2, DestReg).addReg(TmpReg).addImm(Shift-1);
return;
case cShort:
BuildMI(*MBB, IP, X86::SHL16ri,2, DestReg).addReg(TmpReg).addImm(Shift-1);
return;
case cInt:
BuildMI(*MBB, IP, X86::SHL32ri,2, DestReg).addReg(TmpReg).addImm(Shift-1);
return;
}
}
if (Class == cShort) {
BuildMI(*MBB, IP, X86::IMUL16rri,2,DestReg).addReg(op0Reg).addImm(ConstRHS);
@ -2373,7 +2411,7 @@ void ISel::doMultiplyConst(MachineBasicBlock *MBB,
}
// Most general case, emit a normal multiply...
unsigned TmpReg = makeAnotherReg(DestTy);
TmpReg = makeAnotherReg(DestTy);
BuildMI(*MBB, IP, MOVriTab[Class], 1, TmpReg).addImm(ConstRHS);
// Emit a MUL to multiply the register holding the index by