[llvm-dev] SystemZ intrinsics definitions / memory flags (original) (raw)

Ulrich Weigand via llvm-dev llvm-dev at lists.llvm.org
Thu Nov 30 04:37:24 PST 2017

Jonas Paulsson <paulsson at linux.vnet.ibm.com> wrote on 30.11.2017 12:11:56:

* This intrinsic only stores and does not load:

def ints390tbegin : Intrinsic<[llvmi32ty], [llvmptrty,_ _llvmi32ty],_ _[IntrNoDuplicate]>; let mayLoad = 1 in  // WRONG: does not load def TBEGINC : SideEffectBinarySIL<"tbeginc", 0xE561,_ _ints390tbeginc, imm32zx16>; I tried doing [IntrNoDuplicate, WriteOnly<0>], but found that for some reason that didn't work as I had hoped for.

Hmm. While there is a comment by Richard further down in the file:

                             // In fact write-only but there's no

property // for that.

it seems this may no longer be true. Looking at Intrinsics.td, I now see:

// IntrWriteMem - This intrinsic only writes to memory, but does not read from // memory, and has no other side effects. This means dead stores before calls // to this intrinsics may be removed. def IntrWriteMem : IntrinsicProperty;

* Similarly,

def ints390ntstg : Intrinsic<[], [llvmi64ty, llvmptr64ty],_ _[IntrArgMemOnly]>; does not load, but the using instruction must have the mayLoad flag set. Again, WriteOnly<1> does not work. * This intrinsic: def ints390tabort : Intrinsic<[], [llvmi64ty],_ _[IntrNoReturn, Throws]>; should have just the hasSideEffects=1 on the instruction, but per the above intrinsic definition, both mayLoad and mayStore flags are required on the MI.

What about using IntrNoMem plus IntrHasSideEffects ?

* These two set/read the FP control register, and both have reg-reg/mem-reg variants. So EFPC and SFPC actually do not touch memory at all:

def ints390sfpc : GCCBuiltin<"_builtins390sfpc">, Intrinsic<[], [llvmi32ty], []>; def ints390efpc : GCCBuiltin<"_builtins390efpc">, Intrinsic<[llvmi32ty], [], []>; let mayLoad = 1, mayStore = 1 in { def EFPC  : InherentRRE<"efpc", 0xB38C, GR32,_ _ints390efpc>;           // no-mem def STFPC : StoreInherentS<"stfpc", 0xB29C, storei, 4>;  // stores def SFPC : SideEffectUnaryRRE<"sfpc", 0xB384, GR32,_ _ints390sfpc>;      // no-mem def LFPC : SideEffectUnaryS<"lfpc", 0xB29D, loadu, 4>;>;  // loads } Is the proper solution in this case to make a duplicate version for each intrinsic that does not touch memory?

I'd just use IntrNoMem here. The variants that match the mem-reg cases will have both the intrinsic and a load/store node in the DAG, and will inherit the mayLoad / mayStore property from the latter node.

Bye, Ulrich -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20171130/3f0fc4d8/attachment.html>

More information about the llvm-dev mailing list