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ARM: use litpools for normal i32 imms when compiling minsize.

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With constant-sharing, litpool loads consume 4 + N*2 bytes of code, but
movw/movt pairs consume 8*N. This means litpools are better than movw/movt even
with just one use. Other materialisation strategies can still be better though,
so the logic is a little odd.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199891 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Tim Northover
2014-01-23 13:43:47 +00:00
parent 37106321f8
commit 1334acd8c6
4 changed files with 70 additions and 11 deletions
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20
lib/Target/ARM/ARMISelDAGToDAG.cpp
View File

@@ -2472,19 +2472,21 @@ SDNode *ARMDAGToDAGISel::Select(SDNode *N) {
case ISD::Constant: {
unsigned Val = cast<ConstantSDNode>(N)->getZExtValue();
bool UseCP = true;
if (Subtarget->hasThumb2())
if (Subtarget->useMovt())
// Thumb2-aware targets have the MOVT instruction, so all immediates can
// be done with MOV + MOVT, at worst.
UseCP = 0;
UseCP = false;
else {
if (Subtarget->isThumb()) {
UseCP = (Val > 255 && // MOV
~Val > 255 && // MOV + MVN
!ARM_AM::isThumbImmShiftedVal(Val)); // MOV + LSL
UseCP = (Val > 255 && // MOV
~Val > 255 && // MOV + MVN
!ARM_AM::isThumbImmShiftedVal(Val) && // MOV + LSL
!(Subtarget->hasV6T2Ops() && Val <= 0xffff)); // MOVW
} else
UseCP = (ARM_AM::getSOImmVal(Val) == -1 && // MOV
ARM_AM::getSOImmVal(~Val) == -1 && // MVN
!ARM_AM::isSOImmTwoPartVal(Val)); // two instrs.
UseCP = (ARM_AM::getSOImmVal(Val) == -1 && // MOV
ARM_AM::getSOImmVal(~Val) == -1 && // MVN
!ARM_AM::isSOImmTwoPartVal(Val) && // two instrs.
!(Subtarget->hasV6T2Ops() && Val <= 0xffff)); // MOVW
}
if (UseCP) {
@@ -2494,7 +2496,7 @@ SDNode *ARMDAGToDAGISel::Select(SDNode *N) {
getTargetLowering()->getPointerTy());
SDNode *ResNode;
if (Subtarget->isThumb1Only()) {
if (Subtarget->isThumb()) {
SDValue Pred = getAL(CurDAG);
SDValue PredReg = CurDAG->getRegister(0, MVT::i32);
SDValue Ops[] = { CPIdx, Pred, PredReg, CurDAG->getEntryNode() };

2
lib/Target/ARM/ARMInstrInfo.td
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@@ -593,7 +593,7 @@ def so_imm2part : PatLeaf<(imm), [{
/// arm_i32imm - True for +V6T2, or true only if so_imm2part is true.
///
def arm_i32imm : PatLeaf<(imm), [{
if (Subtarget->hasV6T2Ops())
if (Subtarget->useMovt())
return true;
return ARM_AM::isSOImmTwoPartVal((unsigned)N->getZExtValue());
}]>;

2
lib/Target/ARM/ARMInstrThumb2.td
View File

@@ -3781,7 +3781,7 @@ def t2SUBS_PC_LR : T2I <(outs), (ins imm0_255:$imm), NoItinerary,
let isReMaterializable = 1, isMoveImm = 1 in
def t2MOVi32imm : PseudoInst<(outs rGPR:$dst), (ins i32imm:$src), IIC_iMOVix2,
[(set rGPR:$dst, (i32 imm:$src))]>,
Requires<[IsThumb, HasV6T2]>;
Requires<[IsThumb, UseMovt]>;
// Pseudo instruction that combines movw + movt + add pc (if pic).
// It also makes it possible to rematerialize the instructions.