[llvm-dev] Avoiding during my pass the optimization (copy propagation) of my LLVM IR code (at generation)

[Alex Susu via llvm-dev]

   Hello.
     I'm writing an LLVM pass that is working on LLVM IR.
     To my surprise the following LLVM pass code generates optimized code - it does copy 
propagation on it.
       Value *vecShuffleOnePtr = Builder.CreateGEP(ptr_B, vecShuffleOne, "VectorGep");
       ...
       packed_gather_params.push_back(vecShuffleOnePtr);
       CallInst *callGather = Builder.CreateCall(func_llvm_masked_gather_v128i16,
                                                 packed_gather_params);
       callGather->addAttribute(AttributeSet::FunctionIndex, Attribute::NoUnwind);

       DEBUG(dbgs() << "callGather: " << *callGather << "\n");

     When running this code we get at stderr something like:
         callgather: %50 = call <4 x i16> @llvm.masked.gather.v4i16(<4 x i16*> 
getelementptr (i16, i16* inttoptr (i16 51 to i16*), <4 x i64> <i64 1, i64 1, i64 1, i64 
1>), i32 0, <4 x i1> <i1 true, i1 true, i1 true, i1 true>, <4 x i16> undef)
     Also, more importantly, the resulting LLVM program will also contain this 1 gather 
LLVM IR instruction.

     So, although I instructed LLVM to generate 2 instructions, it creates only one 
instruction, a call to gather containing as parameter not the VectorGep variable name, but 
its value/definition, the getelementptr instruction (and this happens even if VectorGep is 
used more than once in my program).

     Is there a way to specify programmatically in my LLVM pass to avoid doing this copy 
propagation optimization (and obtain an LLVM program with a separate getelementptr 
instruction, besides the gather instruction)?

   Thank you,
     Alex