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Emit x86 instructions for: A = B op C, where A and B are 16-bit registers,

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C is a constant which can be sign-extended from 8 bits without value loss,
and op is one of: add, sub, imul, and, or, xor.

This allows the JIT to emit the one byte version of the constant instead of
the two or 4 byte version.  Because these instructions are very common, this
can save a LOT of code space.  For example, I sampled two benchmarks, 176.gcc
and 254.gap.

BM        Old     New    Reduction
176.gcc 2673621 2548962  4.89%
254.gap  498261  475104  4.87%

Note that while the percentage is not spectacular, this did eliminate
124.6 _KILOBYTES_ of codespace from gcc.  Not bad.

Note that this doesn't effect the llc version at all, because the assembler
already does this optimization.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@9284 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
2003-10-20 05:53:31 +00:00
parent e738656c0b
commit 43a5ff8d40
3 changed files with 94 additions and 0 deletions
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40
lib/Target/X86/PeepholeOptimizer.cpp
View File

@@ -51,6 +51,46 @@ bool PH::PeepholeOptimize(MachineBasicBlock &MBB,
}
return false;
// A large number of X86 instructions have forms which take an 8-bit
// immediate despite the fact that the operands are 16 or 32 bits. Because
// this can save three bytes of code size (and icache space), we want to
// shrink them if possible.
case X86::ADDri16: case X86::ADDri32:
case X86::SUBri16: case X86::SUBri32:
case X86::IMULri16: case X86::IMULri32:
case X86::ANDri16: case X86::ANDri32:
case X86::ORri16: case X86::ORri32:
case X86::XORri16: case X86::XORri32:
assert(MI->getNumOperands() == 3 && "These should all have 3 operands!");
if (MI->getOperand(2).isImmediate()) {
int Val = MI->getOperand(2).getImmedValue();
// If the value is the same when signed extended from 8 bits...
if (Val == (signed int)(signed char)Val) {
unsigned Opcode;
switch (MI->getOpcode()) {
default: assert(0 && "Unknown opcode value!");
case X86::ADDri16: Opcode = X86::ADDri16b; break;
case X86::ADDri32: Opcode = X86::ADDri32b; break;
case X86::SUBri16: Opcode = X86::SUBri16b; break;
case X86::SUBri32: Opcode = X86::SUBri32b; break;
case X86::IMULri16: Opcode = X86::IMULri16b; break;
case X86::IMULri32: Opcode = X86::IMULri32b; break;
case X86::ANDri16: Opcode = X86::ANDri16b; break;
case X86::ANDri32: Opcode = X86::ANDri32b; break;
case X86::ORri16: Opcode = X86::ORri16b; break;
case X86::ORri32: Opcode = X86::ORri32b; break;
case X86::XORri16: Opcode = X86::XORri16b; break;
case X86::XORri32: Opcode = X86::XORri32b; break;
}
unsigned R0 = MI->getOperand(0).getReg();
unsigned R1 = MI->getOperand(1).getReg();
*I = BuildMI(Opcode, 2, R0).addReg(R1).addZImm((char)Val);
delete MI;
return true;
}
}
return false;
#if 0
case X86::MOVir32: Size++;
case X86::MOVir16: Size++;