6502/llvm-6502
1
0
Fork 0
mirror of https://github.com/c64scene-ar/llvm-6502.git synced 2025-11-03 14:21:30 +00:00
Code Issues Projects Releases Wiki Activity

[ARM64] Prevent bit extraction to be adjusted by following shift

Browse Source 
For pattern like ((x >> C1) & Mask) << C2, DAG combiner may convert it
into (x >> (C1-C2)) & (Mask << C2), which makes pattern matching of ubfx
more difficult.
For example:
Given
  %shr = lshr i64 %x, 4
  %and = and i64 %shr, 15
  %arrayidx = getelementptr inbounds [8 x [64 x i64]]* @arr, i64 0, %i64 2, i64 %and
  %0 = load i64* %arrayidx
With current shift folding, it takes 3 instrs to compute base address:
  lsr x8, x0, #1
  and x8, x8, #0x78
  add x8, x9, x8

If using ubfx, it only needs 2 instrs:
  ubfx  x8, x0, #4, #4
  add x8, x9, x8, lsl #3

This fixes bug 19589


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207702 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Weiming Zhao
2014-04-30 21:07:24 +00:00
parent 79844fc3d2
commit fa1cf8cd68
5 changed files with 43 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files

15
lib/Target/ARM64/ARM64ISelLowering.cpp
View File

@@ -5931,6 +5931,21 @@ ARM64TargetLowering::getScratchRegisters(CallingConv::ID) const {
return ScratchRegs;
}
bool ARM64TargetLowering::isDesirableToCommuteWithShift(const SDNode *N) const {
EVT VT = N->getValueType(0);
// If N is unsigned bit extraction: ((x >> C) & mask), then do not combine
// it with shift to let it be lowered to UBFX.
if (N->getOpcode() == ISD::AND && (VT == MVT::i32 || VT == MVT::i64) &&
isa<ConstantSDNode>(N->getOperand(1))) {
uint64_t TruncMask = N->getConstantOperandVal(1);
if (isMask_64(TruncMask) &&
N->getOperand(0).getOpcode() == ISD::SRL &&
isa<ConstantSDNode>(N->getOperand(0)->getOperand(1)))
return false;
}
return true;
}
bool ARM64TargetLowering::shouldConvertConstantLoadToIntImm(const APInt &Imm,
Type *Ty) const {
assert(Ty->isIntegerTy());