Commit Graph

6 Commits

Author SHA1 Message Date
Sjoerd Meijer 9529597cf4 Recommit #2: "[LV] Induction Variable does not remain scalar under tail-folding."
This was reverted because of a miscompilation. At closer inspection, the
problem was actually visible in a changed llvm regression test too. This
one-line follow up fix/recommit will splat the IV, which is what we are trying
to avoid if unnecessary in general, if tail-folding is requested even if all
users are scalar instructions after vectorisation. Because with tail-folding,
the splat IV will be used by the predicate of the masked loads/stores
instructions. The previous version omitted this, which caused the
miscompilation. The original commit message was:

If tail-folding of the scalar remainder loop is applied, the primary induction
variable is splat to a vector and used by the masked load/store vector
instructions, thus the IV does not remain scalar. Because we now mark
that the IV does not remain scalar for these cases, we don't emit the vector IV
if it is not used. Thus, the vectoriser produces less dead code.

Thanks to Ayal Zaks for the direction how to fix this.
2020-05-13 13:50:09 +01:00
Benjamin Kramer f936457f80 Revert "Recommit "[LV] Induction Variable does not remain scalar under tail-folding.""
This reverts commit ae45b4dbe7. It
causes miscompilations, test case on the mailing list.
2020-05-08 14:49:10 +02:00
Sjoerd Meijer ae45b4dbe7 Recommit "[LV] Induction Variable does not remain scalar under tail-folding."
With 3 llvm regr tests fixed/updated that I had missed.
2020-05-07 11:52:20 +01:00
Sjoerd Meijer 20d67ffeae Revert "[LV] Induction Variable does not remain scalar under tail-folding."
This reverts commit 617aa64c84.

while I investigate buildbot failures.
2020-05-07 09:29:56 +01:00
Sjoerd Meijer 617aa64c84 [LV] Induction Variable does not remain scalar under tail-folding.
If tail-folding of the scalar remainder loop is applied, the primary induction
variable is splat to a vector and used by the masked load/store vector
instructions, thus the IV does not remain scalar. Because we now mark
that the IV does not remain scalar for these cases, we don't emit the vector IV
if it is not used. Thus, the vectoriser produces less dead code.

Thanks to Ayal Zaks for the direction how to fix this.

Differential Revision: https://reviews.llvm.org/D78911
2020-05-07 09:15:23 +01:00
Florian Hahn f14f2a8568 [LV] Fix predication for branches with matching true and false succs.
Currently due to the edge caching, we create wrong predicates for
branches with matching true and false successors. We will cache the
condition for the edge from the true successor, and then lookup the same
edge (src and dst are the same) for the edge to the false successor.

If both successors match, the condition should always be true. At the
moment, we cannot really create constant VPValues, but we can just
create a true condition as X | !X. Later passes will clean that up.

Fixes PR44488.

Reviewers: rengolin, hsaito, fhahn, Ayal, dorit, gilr

Reviewed By: Ayal

Differential Revision: https://reviews.llvm.org/D73079
2020-01-22 18:34:11 -08:00