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Fix a minor code-quality issue. When passing 8 and 16-bit integer constants

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to function calls, we would emit dead code, like this:

int Y(int, short, double);
int X() {
  Y(4, 123, 4);
}

--- Old
X:
        sub %ESP, 20
        mov %EAX, 4
        mov DWORD PTR [%ESP], %EAX
***     mov %AX, 123
        mov %AX, 123
        movsx %EAX, %AX
        mov DWORD PTR [%ESP + 4], %EAX
        fld QWORD PTR [.CPIX_0]
        fstp QWORD PTR [%ESP + 8]
        call Y
        mov %EAX, 0
        # IMPLICIT_USE %EAX %ESP
        add %ESP, 20
        ret

Now we emit:
X:
        sub %ESP, 20
        mov %EAX, 4
        mov DWORD PTR [%ESP], %EAX
        mov %AX, 123
        movsx %EAX, %AX
        mov DWORD PTR [%ESP + 4], %EAX
        fld QWORD PTR [.CPIX_0]
        fstp QWORD PTR [%ESP + 8]
        call Y
        mov %EAX, 0
        # IMPLICIT_USE %EAX %ESP
        add %ESP, 20
        ret

Next up, eliminate the mov AX and movsx entirely!

llvm-svn: 12026
This commit is contained in:
Chris Lattner 2004-03-01 02:34:08 +00:00
parent 176413cedb
commit c686a9ab37
1 changed files with 4 additions and 1 deletions
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5
lib/Target/X86/InstSelectSimple.cpp
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@ -1098,7 +1098,7 @@ void ISel::doCall(const ValueRecord &Ret, MachineInstr *CallMI,
// Arguments go on the stack in reverse order, as specified by the ABI.
unsigned ArgOffset = 0;
for (unsigned i = 0, e = Args.size(); i != e; ++i) {
unsigned ArgReg = Args[i].Val ? getReg(Args[i].Val) : Args[i].Reg;
unsigned ArgReg;
switch (getClassB(Args[i].Ty)) {
case cByte:
case cShort: {
@ -1110,10 +1110,12 @@ void ISel::doCall(const ValueRecord &Ret, MachineInstr *CallMI,
break;
}
case cInt:
ArgReg = Args[i].Val ? getReg(Args[i].Val) : Args[i].Reg;
addRegOffset(BuildMI(BB, X86::MOV32mr, 5),
X86::ESP, ArgOffset).addReg(ArgReg);
break;
case cLong:
ArgReg = Args[i].Val ? getReg(Args[i].Val) : Args[i].Reg;
addRegOffset(BuildMI(BB, X86::MOV32mr, 5),
X86::ESP, ArgOffset).addReg(ArgReg);
addRegOffset(BuildMI(BB, X86::MOV32mr, 5),
@ -1122,6 +1124,7 @@ void ISel::doCall(const ValueRecord &Ret, MachineInstr *CallMI,
break;
case cFP:
ArgReg = Args[i].Val ? getReg(Args[i].Val) : Args[i].Reg;
if (Args[i].Ty == Type::FloatTy) {
addRegOffset(BuildMI(BB, X86::FST32m, 5),
X86::ESP, ArgOffset).addReg(ArgReg);