Sanjay Patel b6404a8ca6 [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

llvm-svn: 319964

2017-12-06 21:22:57 +00:00

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