[PATCH] D20058: [SCEV] No-wrap flags are not propagated when folding "{S, +, X}+T ==> {S+T, +, X}"

[Oleg Ranevskyy via llvm-commits]

iid_iunknown added a comment.

Could you elaborate on this part of your comment, please?

  with `CHECK:` lines verifying that the `sext` instructions don't get mapped to `sext` SCEV expressions.

A piece from my modified test that exposes the problem:

  for.body3:
    %i.16 = phi i32 [ %inc5, %for.body3 ], [ %i.0.lcssa, %for.cond1.preheader ]
    %sub = add nsw i32 %i.16, -2
    %idxprom = sext i32 %sub to i64
    %arrayidx = getelementptr inbounds [10 x i32], [10 x i32]* %arr, i64 0, i64 %idxprom

The patch eliminates %idxprom and uses an introduced %indvars.iv for array indexing. I am not sure this is something that can be well tested with `opt -analyze -scalar-evolution`. Opt shows different outputs with and w/o the patch, but these differences mainly relate to moving the constants outside of 'sext'. E.g.:

**Patched:**

  %idxprom = sext i32 %sub to i64
    -->  {(-2 + (sext i32 %i.0.lcssa to i64))<nsw>,+,1}<nsw><%for.body3> U: [-2147483650,4294967304) S: [-2147483650,4294967304)		Exits: (-2 + (zext i32 (9 + (-1 * %i.0.lcssa)) to i64) + (sext i32 %i.0.lcssa to i64))

**No patch:**

  %idxprom = sext i32 %sub to i64
    -->  {(sext i32 (-2 + %i.0.lcssa) to i64),+,1}<nsw><%for.body3> U: [-2147483648,4294967306) S: [-2147483648,4294967306)		Exits: ((zext i32 (9 + (-1 * %i.0.lcssa)) to i64) + (sext i32 (-2 + %i.0.lcssa) to i64))

//(Patch gives "(-2 + (sext i32 %i.0.lcssa to i64))<nsw>" instead of "(sext i32 (-2 + %i.0.lcssa) to i64)").//

My idea was to check that %idxprom gets eliminated and the array is indexed by an expression w/o 'sext'. This can be done by `opt -indvars` (`-analyze` is not useful for `-indvars` as IndVarsSimplify::print() is not defined).

Is this is what the test is expected to do or you have a different idea?

Thanks.


Repository:
  rL LLVM

http://reviews.llvm.org/D20058