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author | Sameer AbuAsal <sabuasal@codeaurora.org> | 2018-05-17 18:14:53 +0000 |
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committer | Sameer AbuAsal <sabuasal@codeaurora.org> | 2018-05-17 18:14:53 +0000 |
commit | 6c8d8d769f5f81a512133877ad06681c46be1d2d (patch) | |
tree | d4d672b00696525ffb6d8ab6a7effdd8afce5037 /lib/Target/RISCV | |
parent | 03da9798c111f46d726e5ac6873403330d53da27 (diff) |
[RISCV] Separate base from offset in lowerGlobalAddress
Summary:
When lowering global address, lower the base as a TargetGlobal first then
create an SDNode for the offset separately and chain it to the address calculation
This optimization will create a DAG where the base address of a global access will
be reused between different access. The offset can later be folded into the immediate
part of the memory access instruction.
With this optimization we generate:
lui a0, %hi(s)
addi a0, a0, %lo(s) ; shared base address.
addi a1, zero, 20 ; 2 instructions per access.
sw a1, 44(a0)
addi a1, zero, 10
sw a1, 8(a0)
addi a1, zero, 30
sw a1, 80(a0)
Instead of:
lui a0, %hi(s+44) ; 3 instructions per access.
addi a1, zero, 20
sw a1, %lo(s+44)(a0)
lui a0, %hi(s+8)
addi a1, zero, 10
sw a1, %lo(s+8)(a0)
lui a0, %hi(s+80)
addi a1, zero, 30
sw a1, %lo(s+80)(a0)
Which will save one instruction per access.
Reviewers: asb, apazos
Reviewed By: asb
Subscribers: rbar, johnrusso, simoncook, jordy.potman.lists, niosHD, kito-cheng, shiva0217, zzheng, edward-jones, mgrang, apazos, asb, llvm-commits
Differential Revision: https://reviews.llvm.org/D46989
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@332641 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/Target/RISCV')
-rw-r--r-- | lib/Target/RISCV/RISCVISelLowering.cpp | 15 |
1 files changed, 10 insertions, 5 deletions
diff --git a/lib/Target/RISCV/RISCVISelLowering.cpp b/lib/Target/RISCV/RISCVISelLowering.cpp index 52c027ba314..d3d0d0370b9 100644 --- a/lib/Target/RISCV/RISCVISelLowering.cpp +++ b/lib/Target/RISCV/RISCVISelLowering.cpp @@ -293,17 +293,22 @@ SDValue RISCVTargetLowering::lowerGlobalAddress(SDValue Op, GlobalAddressSDNode *N = cast<GlobalAddressSDNode>(Op); const GlobalValue *GV = N->getGlobal(); int64_t Offset = N->getOffset(); + MVT XLenVT = Subtarget.getXLenVT(); if (isPositionIndependent() || Subtarget.is64Bit()) report_fatal_error("Unable to lowerGlobalAddress"); - - SDValue GAHi = - DAG.getTargetGlobalAddress(GV, DL, Ty, Offset, RISCVII::MO_HI); - SDValue GALo = - DAG.getTargetGlobalAddress(GV, DL, Ty, Offset, RISCVII::MO_LO); + // In order to maximise the opportunity for common subexpression elimination, + // emit a separate ADD node for the global address offset instead of folding + // it in the global address node. Later peephole optimisations may choose to + // fold it back in when profitable. + SDValue GAHi = DAG.getTargetGlobalAddress(GV, DL, Ty, 0, RISCVII::MO_HI); + SDValue GALo = DAG.getTargetGlobalAddress(GV, DL, Ty, 0, RISCVII::MO_LO); SDValue MNHi = SDValue(DAG.getMachineNode(RISCV::LUI, DL, Ty, GAHi), 0); SDValue MNLo = SDValue(DAG.getMachineNode(RISCV::ADDI, DL, Ty, MNHi, GALo), 0); + if (Offset != 0) + return DAG.getNode(ISD::ADD, DL, Ty, MNLo, + DAG.getConstant(Offset, DL, XLenVT)); return MNLo; } |