[X86][AArch64][DAGCombine] Unfold 'check for [no] signed truncation' pattern

Authored by lebedev.ri on Jul 16 2018, 5:44 AM.


[X86][AArch64][DAGCombine] Unfold 'check for [no] signed truncation' pattern



As discussed in https://reviews.llvm.org/D49179#1158957 and later,
the IR for 'check for [no] signed truncation' pattern can be improved:
^ that pattern will be produced by Implicit Integer Truncation sanitizer,
https://reviews.llvm.org/D48958 https://bugs.llvm.org/show_bug.cgi?id=21530
in signed case, therefore it is probably a good idea to improve it.

But the IR-optimal patter does not lower efficiently, so we want to undo it..

This handles the simple pattern.
There is a second pattern with predicate and constants inverted.

NOTE: we do not check uses here. we always do the transform.

Reviewers: spatel, craig.topper, RKSimon, javed.absar

Reviewed By: spatel

Subscribers: kristof.beyls, llvm-commits

Differential Revision: https://reviews.llvm.org/D49266

llvm-svn: 337166