[InstCombine] canonicalize constant-minus-boolean to select-of-constants
This restores the half of:
https://reviews.llvm.org/rL75531
that was reverted at:
https://reviews.llvm.org/rL159230
For the x86 case mentioned there, we now produce:
leal 1(%rdi), %eax
subl %esi, %eax
We have target hooks to invert this in DAGCombiner (and x86 is enabled) with:
https://reviews.llvm.org/rL296977
https://reviews.llvm.org/rL311731
AArch64 and possibly other targets would probably benefit from enabling those hooks too.
See PR30327:
https://bugs.llvm.org/show_bug.cgi?id=30327#c2
Differential Revision: https://reviews.llvm.org/D40612
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@319964
91177308-0d34-0410-b5e6-
96231b3b80d8