[LLVMdev] Strange code generation issue

[Dibyendu Majumdar]

Correction below:

On 1 August 2015 at 17:36, Dibyendu Majumdar <mobile at majumdar.org.uk> wrote:
> On 1 August 2015 at 15:37, Dibyendu Majumdar <mobile at majumdar.org.uk> wrote:
>> Hi,
>>
>> I am using the LLVM release_37 branch and have a strange issue.
>>
>> Please see the two IR outputs I have saved below:
>>
>> https://github.com/dibyendumajumdar/ravi/tree/master/ravi-tests/comp_issue
>>
>> The original.ll is the code I am generating.
>> The aftercompiling.ll is the output from LLVM with opt level 0.
>>
>> The issue is that LLVM is deciding to remove the blocks with labels
>> updatei and updatei.64 (lines 433 and 454 in original.ll) for some
>> reason that I cannot fathom. This is then causing the program to
>> misbehave.
>>
>> I will check if the same issue occurs in LLVM 3.6.
>>
>
> I seem to get the same issue in 3.6.2.
>
> The issue appears to be in the following area:
>
> Original code:
>
> forloop34_: ; preds = %forbody27_, %forbody21_
> %200 = load i64, i64* %iidx53, !tbaa !17
> %next.idx = add nsw i64 1, %200
> store i64 %next.idx, i64* %iidx53, !tbaa !17
> %201 = load i64, i64* %ilimit52, !tbaa !17
> %idx.gt.limit = icmp sgt i64 %next.idx, %201
> br i1 %idx.gt.limit, label %exit_iforloop, label %updatei
>
> updatei: ; preds = %forloop34_
> %202 = load %struct.TValue*, %struct.TValue** %base, !tbaa !14
> %203 = getelementptr inbounds %struct.TValue, %struct.TValue* %202, i32 12
> %204 = load i64, i64* %iidx53, !tbaa !17
> %205 = bitcast %struct.TValue* %203 to i64*
> store i64 %204, i64* %205, !tbaa !18
> %dest.tt61 = getelementptr inbounds %struct.TValue, %struct.TValue*
> %203, i32 0, i32 1
> store i32 19, i32* %dest.tt61, !tbaa !15
> br label %forbody27_
>
>
> Transformed code:
>
> forloop34_: ; preds = %forbody27_, %forbody21_
> %208 = load i64, i64* %iidx53, !tbaa !17
> %next.idx = add nsw i64 1, %208
> store i64 %next.idx, i64* %iidx53, !tbaa !17
> %209 = load i64, i64* %ilimit52, !tbaa !17
> %idx.gt.limit = icmp sgt i64 %next.idx, %209
> br i1 %idx.gt.limit, label %forloop35_, label %forbody27_
>

forbody27_:                                       ; preds = %forloop34_
  %sunkaddr134 = ptrtoint %struct.CallInfo* %0 to i64
  %sunkaddr135 = add i64 %sunkaddr134, 32
  %sunkaddr136 = inttoptr i64 %sunkaddr135 to %struct.TValue**
  %141 = load %struct.TValue*, %struct.TValue** %sunkaddr136, !tbaa !14
  %142 = getelementptr inbounds %struct.TValue, %struct.TValue* %141, i32 12
  %143 = load i64, i64* %iidx53, !tbaa !17
  %144 = bitcast %struct.TValue* %142 to i64*
  store i64 %143, i64* %144, !tbaa !18
  %dest.tt61 = getelementptr inbounds %struct.TValue, %struct.TValue*
%142, i32 0, i32 1
  store i32 19, i32* %dest.tt61, !tbaa !15


So it seems correct as far as I can make out as presumably
%sunkaddr136 is same as %base.

Regards