[llvm-dev] MachineInstr (and SDNode, LLVM IR Instruction) placeholder for strings

[Alex Susu via llvm-dev]

   Hello.
     I come back to this older thread.
     I would like rephrase the quesion: I want to add strings (containing arithmetic 
expressions, for example) for immediate operands for MachineInstr (possibly also 
MachineSDNode and LLVM IR Instruction) in LLVM since my assembly is let's say interpreted 
at runtime.
     For this I already used inline assembly expressions (or directly SDNode with the 
opcode ISD::INLINEASM), but it's difficult to make sure they stick together with their 
associated Connex instructions (VLOAD, setlc, etc) during all the scheduling and 
Register-allocation passes for llc.

     Did anybody else deal with a similar issue?

   Thank you,
     Alex

On 6/15/2016 2:47 AM, Alex Susu wrote:
>   Hello.
>     David, thank you for pointing out inline assembly expressions.
>     I found: http://clang.llvm.org/compatibility.html#inline-asm and
> http://llvm.org/docs/LangRef.html#inline-assembler-expressions .
>
>     So I added in my LLVM program a line like
>      call void asm sideeffect "MY OWN STRING", "~{dirflag},~{fpsr},~{flags}"() #1
>     and compiled it with llc and it worked as expected.
>
>     More importantly, to programmatically insert assembly expressions in an LLVM pass we
> need to give something like:
>       // Inspired from http://reviews.llvm.org/D15399?id=42353 (see also
> http://stackoverflow.com/questions/28787799/insert-inline-assembly-expressions-using-llvm-pass)
>
>       std::vector<llvm::Value*> Args;
>       Type *ResultType;
>       ResultType = Type::getVoidTy(getGlobalContext());
>
>       // See http://llvm.org/docs/doxygen/html/classllvm_1_1FunctionType.html
>       FunctionType *fTy = FunctionType::get(
>             /* Result */ ResultType,
>             /* NO Params */
>             false);
>       StringRef asmString = "test_ASM_inline_string!";
>       bool hasSideEffect = true;
>       InlineAsm::AsmDialect asmDialect = InlineAsm::AD_ATT;
>
>
>       /*
>        * Note: Extreme care with the constraints.
>        * Info about them at http://llvm.org/docs/LangRef.html#inline-asm-constraint-string
>        *  (and https://doc.rust-lang.org/book/inline-assembly.html)
>        *
>        * When using e.g.:
>        * std::string constraints = "*";
>        * I got this error:
>        *     Assertion `Verify(getFunctionType(), constraints) && "Function type not legal
> for constraints!"' failed.
>        */
>       std::string constraints = "";
>       InlineAsm *iaExpr = InlineAsm::get(fTy, asmString, constraints, hasSideEffect,
>                                     /* IsAlignStack */ false, asmDialect);
>       CallInst *Result = Builder.CreateCall(iaExpr, Args);
>       Result->addAttribute(AttributeSet::FunctionIndex, Attribute::NoUnwind);
>
>   Best regards,
>     Alex
>
>
> On 6/14/2016 12:12 PM, David Chisnall wrote:
>> Hi,
>>
>> Is there a reason that you can’t use inline assembly for this?
>>
>> David
>>
>>> On 13 Jun 2016, at 19:44, Alex Susu via llvm-dev <llvm-dev at lists.llvm.org> wrote:
>>>
>>> Hello. I come back to this thread. But I want to ask a slightly different question.
>>> Is there a way to have LLVM IR language intrinsics that are given at construction
>>> time a string that is written at assembly generation time as it is? (so, basically
>>> having placeholders of strings in LLVM that remain untouched until the end, including
>>> code generation time.)
>>>
>>> More exactly, I would like to give something LIKE this in a middle-tier pass (I
>>> haven't tried this code in LLVM): Value *instrinsicFunc =
>>> Intrinsic::getDeclaration(M, Intrinsic::my_intrinsic);
>>> myIRBuilder.CreateCall(repeatFunc,
>>> "string_that_llc_codegen_should_output_as_assembly"); So my intrinsic would be
>>> accepting a general string which will be used at codegen to be output. I guess I
>>> would have to define it like this in a .td file: def int_my_intrinsic : Intrinsic<[],
>>> [string], []>;
>>>
>>>
>>> The other option that can work but is more complex without any benefit is to define
>>> several intrinsics in the .td files, one for EACH possible string: // To put in the
>>> Intrinsics_....td file: def int_my_intrinsic1 : Intrinsic<[], [], []>; ... def
>>> int_my_intrinsicN : Intrinsic<[], [], []>; // To put in the InstrInfo.td file
>>> something like: def STR_PLACEHOLDER1 : ImmediateInstruction< 0b111111, (outs),
>>> (ins), "string_that_llc_codegen_should_output_as_assembly1", [(int_my_intrinsic1)]
>>> >; def STR_PLACEHOLDER2 : ImmediateInstruction< 0b111110, (outs), (ins),
>>> "string_that_llc_codegen_should_output_as_assembly2", [(int_my_intrinsic2)] >;
>>>
>>>
>>> Best regards, Alex
>>>
>>> On 6/5/2016 5:21 PM, Alex Susu wrote:
>>>> Hello. Hal, the source file you mention (lib/Target/PowerPC/PPCCTRLoops.cpp) makes
>>>> use of LLVM IR intrinsics, in this case defined at
>>>> [LLVM_repo]/llvm/include/llvm/IR/IntrinsicsPowerPC.td, such as: // Intrinsics used
>>>> to generate ctr-based loops. These should only be // generated by the PowerPC
>>>> backend! def int_ppc_mtctr : Intrinsic<[], [llvm_anyint_ty], []>; def
>>>> int_ppc_is_decremented_ctr_nonzero : Intrinsic<[llvm_i1_ty], [], []>;
>>>>
>>>> And these intrinsics are instantiated in the LLVM program, for example with the
>>>> following code in PPCCTRLoops.cpp: IRBuilder<>
>>>> CountBuilder(Preheader->getTerminator()); Module *M =
>>>> Preheader->getParent()->getParent(); Value *MTCTRFunc =
>>>> Intrinsic::getDeclaration(M, Intrinsic::ppc_mtctr,CountType);
>>>> CountBuilder.CreateCall(MTCTRFunc, ECValue);
>>>>
>>>> I have defined also some intrinsics for my loop instructions in my file
>>>> Intrinsics_Connex.td: 1 intrinsic for REPEAT_X_TIMES and 1 for END_REPEAT. /*
>>>> following Intrinsics.td: class Intrinsic<list<LLVMType> ret_types, list<LLVMType>
>>>> param_types = [], list<IntrinsicProperty> properties = [], string name = ""> */ def
>>>> int_connex_repeat_x_times : Intrinsic<[], [], []>; def int_connex_end_repeat :
>>>> Intrinsic<[llvm_i1_ty], [], []>; and added C++ code doing CreateCall() like the one
>>>> above.
>>>>
>>>> I'm looking now at http://llvm.org/docs/ExtendingLLVM.html on how to specify the
>>>> instruction selection of this intrinsic. They write there: "Once the intrinsic has
>>>> been added to the system, you must add code generator support for it. Generally you
>>>> must do the following steps: Add support to the .td file for the target(s) of your
>>>> choice in lib/Target/*/*.td. This is usually a matter of adding a pattern to the
>>>> .td file that matches the intrinsic, though it may obviously require adding the
>>>> instructions you want to generate as well. There are lots of examples in the
>>>> PowerPC and X86 backend to follow."
>>>>
>>>> Then in my pass I create a call to the respective intrinsic: /* See
>>>> http://llvm.org/docs/doxygen/html/classllvm_1_1TargetIntrinsicInfo.html : "Create
>>>> or insert an LLVM Function declaration for an intrinsic, and return it." *   This
>>>> creates a line in the LLVM program like: declare void @llvm.connex.repeat.x.times()
>>>> #2 . *     This line is required, otherwise llc will complain: *        <<error:
>>>> use of undefined value '@llvm.connex.repeat.x.times' call void
>>>> @llvm.connex.repeat.x.times()>> */ Value *repeatFunc =
>>>> Intrinsic::getDeclaration(M, Intrinsic::connex_repeat_x_times);
>>>>
>>>> // See http://llvm.org/docs/doxygen/html/classllvm_1_1IRBuilder.html
>>>> aB.CreateCall(repeatFunc); //, ECValue);
>>>>
>>>>
>>>> Then, in the back end, in InstrInfo.td I write: let hasSideEffects = 1,
>>>> isCodeGenOnly = 1 in { //let Pattern = [(int_connex_repeat_x_times)] in def
>>>> REPEAT_X_TIMES : ImmediateInstruction< 0b111111, (outs), (ins),
>>>> "REPEAT_X_TIMES(1001)", [(int_connex_repeat_x_times)] >; }
>>>>
>>>>
>>>> Then, when I run opt and llc I obtain the expected behavior.
>>>>
>>>> Thank you, Alex
>>>>
>>>>
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