[llvm-dev] [SelectionDAG] Assertion due to MachineMemOperand flags difference.

Sean Fertile via llvm-dev llvm-dev at lists.llvm.org
Fri Oct 13 16:05:39 PDT 2017 

Hello,

I've hit an assertion in SelectionDAG where we try to merge 2 loads
that have the same operands but their MMO flags differ. One is
dereferenceable and one is not. I'm not sure what the underlying issue
here is:

1) MDSDNode with the same operands should have the same flags set on
their respective MMO. The fact the flags differ when the
opcode,types,operands and address-space are the same is the problem.

2) Having MDSDnodes with the same operands but different MMO flags is
possible, so the Flags should be added to the FoldingSetNodeID.

3) Something else I haven't considered.

I have a patch posted implementing 2, but don't know if I should look
at fixing 1 as well (or perhaps instead). The loads that trigger the
assertion are:

t47: v4i32,ch = load<LD16[%0+80](align=8)(dereferenceable)> t20, t46, undef:i64
t69: v4i32,ch = load<LD16[FixedStack1+80](align=8)> t50, t46, undef:i64

I would expect the the second load should also be marked
dereferenceable since its loading from one of the TargetFrames. Am I
on the right track here?

Thanks
Sean
-------------- next part --------------
Initial selection DAG: BB#0 '_Z3fn2v:entry'
SelectionDAG has 122 nodes:
  t4: i64 = GlobalAddress<void (%class.F*)* @_Z10EmitLValuev> 0
  t10: i64 = add Register:i64 %X1, Constant:i64<32>
        t0: ch = EntryToken
      t3: ch = lifetime.start t0, TargetFrameIndex:i64<1>
    t7: ch,glue = callseq_start t3, TargetConstant:i64<32>, TargetConstant:i64<0>
  t12: ch,glue = CopyToReg t7, Register:i64 %X3, FrameIndex:i64<1>
  t16: ch,glue = PPCISD::CALL_NOP t12, TargetGlobalAddress:i64<void (%class.F*)* @_Z10EmitLValuev> 0, Register:i64 %X3, Register:i64 %X2, RegisterMask:Untyped, t12:1
    t17: ch,glue = callseq_end t16, TargetConstant:i64<32>, TargetConstant:i64<0>, t16:1
  t20: ch = lifetime.start t17, TargetFrameIndex:i64<0>
  t21: i64 = Constant<96>
  t22: i64 = Constant<0>
  t24: v4i32,ch = load<LD16[%0](align=8)(dereferenceable)> t20, FrameIndex:i64<1>, undef:i64
  t27: i64 = add FrameIndex:i64<1>, Constant:i64<16>
  t28: v4i32,ch = load<LD16[%0+16](align=8)(dereferenceable)> t20, t27, undef:i64
  t31: i64 = add FrameIndex:i64<1>, Constant:i64<32>
  t32: v4i32,ch = load<LD16[%0+32](align=8)(dereferenceable)> t20, t31, undef:i64
  t36: i64 = add FrameIndex:i64<1>, Constant:i64<48>
  t37: v4i32,ch = load<LD16[%0+48](align=8)(dereferenceable)> t20, t36, undef:i64
  t41: i64 = add FrameIndex:i64<1>, Constant:i64<64>
  t42: v4i32,ch = load<LD16[%0+64](align=8)(dereferenceable)> t20, t41, undef:i64
  t46: i64 = add FrameIndex:i64<1>, Constant:i64<80>
  t47: v4i32,ch = load<LD16[%0+80](align=8)(dereferenceable)> t20, t46, undef:i64
    t25: ch = store<ST16[%1]> t20, t24, FrameIndex:i64<0>, undef:i64
      t29: i64 = add FrameIndex:i64<0>, Constant:i64<16>
    t30: ch = store<ST16[%1+16]> t20, t28, t29, undef:i64
      t33: i64 = add FrameIndex:i64<0>, Constant:i64<32>
    t34: ch = store<ST16[%1+32]> t20, t32, t33, undef:i64
      t38: i64 = add FrameIndex:i64<0>, Constant:i64<48>
    t39: ch = store<ST16[%1+48]> t20, t37, t38, undef:i64
      t43: i64 = add FrameIndex:i64<0>, Constant:i64<64>
    t44: ch = store<ST16[%1+64]> t20, t42, t43, undef:i64
      t48: i64 = add FrameIndex:i64<0>, Constant:i64<80>
    t49: ch = store<ST16[%1+80]> t20, t47, t48, undef:i64
  t50: ch = TokenFactor t24:1, t25, t28:1, t30, t32:1, t34, t37:1, t39, t42:1, t44, t47:1, t49
  t51: i64 = GlobalAddress<void (%class.F*)* @_Z3fn11F> 0
  t53: ch,glue = callseq_start t50, TargetConstant:i64<128>, TargetConstant:i64<0>
  t54: i32 = Constant<96>
  t55: v4i32,ch = load<LD16[FixedStack1](align=8)> t50, FrameIndex:i64<1>, undef:i64
  t57: v4i32,ch = load<LD16[FixedStack1+16](align=8)> t50, t27, undef:i64
  t60: v4i32,ch = load<LD16[FixedStack1+32](align=8)> t50, t31, undef:i64
  t63: v4i32,ch = load<LD16[FixedStack1+48](align=8)> t50, t36, undef:i64
  t66: v4i32,ch = load<LD16[FixedStack1+64](align=8)> t50, t41, undef:i64
  t69: v4i32,ch = load<LD16[FixedStack1+80](align=8)> t50, t46, undef:i64
      t56: ch = store<ST16[<unknown>](align=8)> t50, t55, t10, undef:i64
        t58: i64 = add t10, Constant:i64<16>
      t59: ch = store<ST16[<unknown>](align=8)> t50, t57, t58, undef:i64
        t61: i64 = add t10, Constant:i64<32>
      t62: ch = store<ST16[<unknown>](align=8)> t50, t60, t61, undef:i64
        t64: i64 = add t10, Constant:i64<48>
      t65: ch = store<ST16[<unknown>](align=8)> t50, t63, t64, undef:i64
        t67: i64 = add t10, Constant:i64<64>
      t68: ch = store<ST16[<unknown>](align=8)> t50, t66, t67, undef:i64
        t70: i64 = add t10, Constant:i64<80>
      t71: ch = store<ST16[<unknown>](align=8)> t50, t69, t70, undef:i64
    t72: ch = TokenFactor t55:1, t56, t57:1, t59, t60:1, t62, t63:1, t65, t66:1, t68, t69:1, t71
  t73: ch,glue = callseq_start t72, TargetConstant:i64<128>, TargetConstant:i64<0>
  t74: i64,ch = load<LD8[FixedStack1]> t73, FrameIndex:i64<1>, undef:i64
    t76: i64 = add FrameIndex:i64<1>, Constant:i64<8>
  t77: i64,ch = load<LD8[FixedStack1+8]> t73, t76, undef:i64
  t78: i64,ch = load<LD8[FixedStack1+16]> t73, t27, undef:i64
    t80: i64 = add FrameIndex:i64<1>, Constant:i64<24>
  t81: i64,ch = load<LD8[FixedStack1+24]> t73, t80, undef:i64
  t82: i64,ch = load<LD8[FixedStack1+32]> t73, t31, undef:i64
    t84: i64 = add FrameIndex:i64<1>, Constant:i64<40>
  t85: i64,ch = load<LD8[FixedStack1+40]> t73, t84, undef:i64
  t86: i64,ch = load<LD8[FixedStack1+48]> t73, t36, undef:i64
    t88: i64 = add FrameIndex:i64<1>, Constant:i64<56>
  t89: i64,ch = load<LD8[FixedStack1+56]> t73, t88, undef:i64
    t90: ch = TokenFactor t74:1, t77:1, t78:1, t81:1, t82:1, t85:1, t86:1, t89:1
  t91: ch,glue = CopyToReg t90, Register:i64 %X3, t74
  t93: ch,glue = CopyToReg t91, Register:i64 %X4, t77, t91:1
  t95: ch,glue = CopyToReg t93, Register:i64 %X5, t78, t93:1
  t97: ch,glue = CopyToReg t95, Register:i64 %X6, t81, t95:1
  t99: ch,glue = CopyToReg t97, Register:i64 %X7, t82, t97:1
  t101: ch,glue = CopyToReg t99, Register:i64 %X8, t85, t99:1
  t103: ch,glue = CopyToReg t101, Register:i64 %X9, t86, t101:1
  t105: ch,glue = CopyToReg t103, Register:i64 %X10, t89, t103:1
  t107: ch,glue = PPCISD::CALL_NOP t105, TargetGlobalAddress:i64<void (%class.F*)* @_Z3fn11F> 0, Register:i64 %X3, Register:i64 %X4, Register:i64 %X5, Register:i64 %X6, Register:i64 %X7, Register:i64 %X8, Register:i64 %X9, Register:i64 %X10, Register:i64 %X2, RegisterMask:Untyped, t105:1
  t109: i64 = GlobalAddress<i32 (%class.F*)* @_ZN1F11isGlobalRegEv> 0
      t108: ch,glue = callseq_end t107, TargetConstant:i64<128>, TargetConstant:i64<0>, t107:1
    t110: ch,glue = callseq_start t108, TargetConstant:i64<32>, TargetConstant:i64<0>
  t111: ch,glue = CopyToReg t110, Register:i64 %X3, FrameIndex:i64<0>
  t113: ch,glue = PPCISD::CALL_NOP t111, TargetGlobalAddress:i64<i32 (%class.F*)* @_ZN1F11isGlobalRegEv> 0, Register:i64 %X3, Register:i64 %X2, RegisterMask:Untyped, t111:1
  t114: ch,glue = callseq_end t113, TargetConstant:i64<32>, TargetConstant:i64<0>, t113:1
  t115: i64,ch,glue = CopyFromReg t114, Register:i64 %X3, t114:1
    t117: i64 = AssertSext t115, ValueType:ch:i32
  t118: i32 = truncate t117
      t119: ch = lifetime.end t115:1, TargetFrameIndex:i64<0>
    t120: ch = lifetime.end t119, TargetFrameIndex:i64<1>
  t121: ch = PPCISD::RET_FLAG t120
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