[PATCH] D20789: Consecutive memory access in Loop Vectorizer - fixed and simplified

[Adam Nemet via llvm-commits]

anemet added a comment.

In https://reviews.llvm.org/D20789#503264, @delena wrote:

> This is the output of LoopAccessAnalysis:
>
> W:\ver2>build\Debug\bin\opt.exe -O2 test.ll -S -o test_opt.ll  --debug-only=loop-accesses
>  LAA: Found a loop in _Z23IncrementalCopyFastPathPKcPci: while.body
>  LAA: Processing memory accesses...
>
>   AST: Alias Set Tracker: 1 alias sets for 2 pointer values.
>   AliasSet[0x24f30a0, 2] may alias, No access Pointers: (i64* %2, 18446744073709551615), (i64* %0, 18446744073709551615)
>   
>
> LAA:   Accesses(2):
>
>   %2 = bitcast i8* %op.addr.06 to i64* (write)
>   %0 = bitcast i8* %src.addr.05 to i64* (read-only)
>
> Underlying objects for pointer   %2 = bitcast i8* %op.addr.06 to i64*
>
>   i8* %op
>
> Underlying objects for pointer   %0 = bitcast i8* %src.addr.05 to i64*
>
>   i8* %src
>
> LAA: Found a runtime check ptr:  %2 = bitcast i8* %op.addr.06 to i64*
>  LAA: Found a runtime check ptr:  %0 = bitcast i8* %src.addr.05 to i64*
>  LAA: We need to do 1 pointer comparisons.


LAA says we need a run-time alias check.  Didn't we generate one?

> LAA: We can perform a memory runtime check if needed.

>  LAA: Checking memory dependencies

>  Total Dependences: 0

>  LAA: No unsafe dependent memory operations in loop.  We need runtime memory checks.

>  LAA: Adding RT check for range:

>  Start: %op End: ((8 * (zext i32 ((8 + (-9 smax (-1 + (-1 * %len))) + %len) /u 8) to i64)) + %op)

>  LAA: Adding RT check for range:

>  Start: %src End: ((8 * (zext i32 ((8 + (-9 smax (-1 + (-1 * %len))) + %len) /u 8) to i64)) + %src)

>  LAA: Found a loop in _Z23IncrementalCopyFastPathPKcPci: while.body

>  LAA: Processing memory accesses...

> 

>   AST: Alias Set Tracker: 1 alias sets for 2 pointer values.

>   AliasSet[0x24f3eb0, 2] may alias, No access Pointers: (i64* %231, 18446744073709551615), (i64* %229, 18446744073709551615)

>    

> 

> LAA:   Accesses(2):

> 

>   %231 = bitcast i8* %op.addr.06 to i64* (write)

>   %229 = bitcast i8* %src.addr.05 to i64* (read-only)

> 

> Underlying objects for pointer   %231 = bitcast i8* %op.addr.06 to i64*

> 

>   i8* %op

> 

> Underlying objects for pointer   %229 = bitcast i8* %src.addr.05 to i64*

> 

>   i8* %src

> 

> LAA: Found a runtime check ptr:  %231 = bitcast i8* %op.addr.06 to i64*

>  LAA: Found a runtime check ptr:  %229 = bitcast i8* %src.addr.05 to i64*

>  LAA: We need to do 1 pointer comparisons.

>  LAA: We can perform a memory runtime check if needed.

>  LAA: Checking memory dependencies

>  Total Dependences: 0

>  LAA: No unsafe dependent memory operations in loop.  We need runtime memory checks.

>  LAA: Found a loop in _Z23IncrementalCopyFastPathPKcPci: vector.body

>  LAA: SCEV could not compute the loop exit count.





Repository:
  rL LLVM

https://reviews.llvm.org/D20789