[llvm] r191122 - LoopVectorizer: Only allow vectorization of intrinsics. We can't know for sure that the functions 'abs' or 'round' are the functions from libm.

[Hal Finkel]

Nadav,

This represents a major functionality regression. The entire TLI infrastructure depends on matching functions by name, and this is no different. Are you going to have the frontend turn all of these into intrinsics, and only when math.h in included?

In any case, all of those names are reserved (when used as identifiers with external linkage), at least in C (according to section 7.1.3 Reserved identifiers). Could the user specify -fno-builtins?

Thanks again,
Hal

----- Original Message -----
> Author: nadav
> Date: Fri Sep 20 19:27:05 2013
> New Revision: 191122
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=191122&view=rev
> Log:
> LoopVectorizer: Only allow vectorization of intrinsics. We can't know
> for sure that the functions 'abs' or 'round' are the functions from
> libm.
> 
> rdar://15012650
> 
> 
> Modified:
>     llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp
>     llvm/trunk/test/Transforms/LoopVectorize/intrinsic.ll
> 
> Modified: llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp?rev=191122&r1=191121&r2=191122&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp (original)
> +++ llvm/trunk/lib/Transforms/Vectorize/LoopVectorize.cpp Fri Sep 20
> 19:27:05 2013
> @@ -2925,9 +2925,18 @@ bool LoopVectorizationLegality::canVecto
>        // We still don't handle functions. However, we can ignore dbg
>        intrinsic
>        // calls and we do handle certain intrinsic and libm
>        functions.
>        CallInst *CI = dyn_cast<CallInst>(it);
> -      if (CI && !getIntrinsicIDForCall(CI, TLI) &&
> !isa<DbgInfoIntrinsic>(CI)) {
> +      if (CI) {
>          DEBUG(dbgs() << "LV: Found a call site.\n");
> -        return false;
> +
> +        if (!isa<IntrinsicInst>(it)) {
> +          DEBUG(dbgs() << "LV: We only vectorize intrinsics.\n");
> +          return false;
> +        }
> +
> +        if (!getIntrinsicIDForCall(CI, TLI) &&
> !isa<DbgInfoIntrinsic>(CI)) {
> +          DEBUG(dbgs() << "LV: Found an unknown intrinsic.\n");
> +          return false;
> +        }
>        }
>  
>        // Check that the instruction return type is vectorizable.
> 
> Modified: llvm/trunk/test/Transforms/LoopVectorize/intrinsic.ll
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopVectorize/intrinsic.ll?rev=191122&r1=191121&r2=191122&view=diff
> ==============================================================================
> --- llvm/trunk/test/Transforms/LoopVectorize/intrinsic.ll (original)
> +++ llvm/trunk/test/Transforms/LoopVectorize/intrinsic.ll Fri Sep 20
> 19:27:05 2013
> @@ -1018,7 +1018,7 @@ for.body:
>    %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body
>    ]
>    %arrayidx = getelementptr inbounds float* %x, i64 %indvars.iv
>    %0 = load float* %arrayidx, align 4
> -  %call = tail call float @fabsf(float %0) nounwind readnone
> +  %call = tail call float @llvm.fabs.f32(float %0) nounwind readnone
>    store float %call, float* %arrayidx, align 4
>    %indvars.iv.next = add i64 %indvars.iv, 1
>    %lftr.wideiv = trunc i64 %indvars.iv.next to i32
> @@ -1029,6 +1029,31 @@ for.end:
>    ret void
>  }
>  
> -declare float @fabsf(float) nounwind readnone
> -
>  declare double @llvm.pow.f64(double, double) nounwind readnone
> +
> +
> +;CHECK: @not_intrin
> +;CHECK: @round
> +;CHECK-NOT: @round
> +;CHECK: ret
> +define void @not_intrin(i32* nocapture %A) nounwind ssp uwtable {
> +  br label %1
> +
> +; <label>:1                                       ; preds = %1, %0
> +  %indvars.iv = phi i64 [ 0, %0 ], [ %indvars.iv.next, %1 ]
> +  %2 = getelementptr inbounds i32* %A, i64 %indvars.iv
> +  %3 = load i32* %2, align 4
> +  %4 = add nsw i32 %3, 3
> +  store i32 %4, i32* %2, align 4
> +  %5 = trunc i64 %indvars.iv to i32
> +  tail call void @round(i32 %5) nounwind
> +  %indvars.iv.next = add i64 %indvars.iv, 1
> +  %lftr.wideiv = trunc i64 %indvars.iv.next to i32
> +  %exitcond = icmp eq i32 %lftr.wideiv, 256
> +  br i1 %exitcond, label %6, label %1
> +
> +; <label>:6                                       ; preds = %1
> +  ret void
> +}
> +
> +declare void @round(i32)
> 
> 
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-- 
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory