Assertion failure on isFast "getting fast-math flag on invalid op", Trying to check if fast option is set for an instruction

IR & Optimizations
1

Hi I am writing a transformation pass to check where on some conditional call instruction I would like to check If fast option is set for that call, instruction and disable it. For example on below call inst, I would like to disable the fast option.

  %call3 = call fast fastcc noundef <8 x float> @_ZL13_mm256_mul_psDv8_fS_(<8 x float> noundef %0, <8 x float> noundef %power.0)

Below is my pass, Don’t mind If I miss something trivial, I’m at a very early stage in compiler dev.


#include "llvm/Transforms/Scalar/RemoveFastFlagsToPreventFma.h"
#include "llvm/IR/Instructions.h"
#define Status(b) outs()<<(b?"Yes\n":"No\n")
using namespace llvm;
using namespace std;

bool fastflags_for_intrfma = false;

bool IsArithmeticIntrinsicCall(const Instruction &i){
    return 1;
}

PreservedAnalyses RemoveFastFlagsToPreventFmaPass::run(Module &M, ModuleAnalysisManager &AM){
    for(Function &F : M){
        for(BasicBlock &b : F){
            for(Instruction &i : b){
               CallInst *call = dyn_cast<CallInst>(&i);
               if(fastflags_for_intrfma==false and (call!=nullptr) and IsArithmeticIntrinsicCall(i)){
                    if(i.isFast()) i.setFast(false);
               }
            }
        }
    }
    for(Function &F : M){
        for(BasicBlock &b : F){
            for(Instruction &i : b){
               CallInst *call = dyn_cast<CallInst>(&i);
               if(fastflags_for_intrfma==false and (call!=nullptr) and IsArithmeticIntrinsicCall(i)){
                  Status(i.isFast());
               }
            }
        }
    }
    return PreservedAnalyses::all();
}

The Assertion failure :

opt: llvm-project/llvm/lib/IR/Instruction.cpp:250: bool llvm::Instruction::isFast() const: Assertion `isa<FPMathOperator>(this) && "getting fast-math flag on invalid op"' failed.
2

What is your question? The assertion message is rather clear. You can only call isFast on FPMathOperator instructions but your code doesn’t check against this.

1 Like
3

Yes got it thanks.