[InstSimplify] fold icmp based on range of abs/nabs (2nd try)
This is retrying the fold from rL345717
(reverted at rL347780)
...with a fix for the miscompile
demonstrated by PR39510:
https://bugs.llvm.org/show_bug.cgi?id=39510
Original commit message:
This is a fix for PR39475:
https://bugs.llvm.org/show_bug.cgi?id=39475
We managed to get some of these patterns using computeKnownBits in https://reviews.llvm.org/D47041, but that
can't be used for nabs(). Instead, put in some range-based logic, so we can fold
both abs/nabs with icmp with a constant value.
Alive proofs:
https://rise4fun.com/Alive/21r
Name: abs_nsw_is_positive
%cmp = icmp slt i32 %x, 0
%negx = sub nsw i32 0, %x
%abs = select i1 %cmp, i32 %negx, i32 %x
%r = icmp sgt i32 %abs, -1
=>
%r = i1 true
Name: abs_nsw_is_not_negative
%cmp = icmp slt i32 %x, 0
%negx = sub nsw i32 0, %x
%abs = select i1 %cmp, i32 %negx, i32 %x
%r = icmp slt i32 %abs, 0
=>
%r = i1 false
Name: nabs_is_negative_or_0
%cmp = icmp slt i32 %x, 0
%negx = sub i32 0, %x
%nabs = select i1 %cmp, i32 %x, i32 %negx
%r = icmp slt i32 %nabs, 1
=>
%r = i1 true
Name: nabs_is_not_over_0
%cmp = icmp slt i32 %x, 0
%negx = sub i32 0, %x
%nabs = select i1 %cmp, i32 %x, i32 %negx
%r = icmp sgt i32 %nabs, 0
=>
%r = i1 false
Differential Revision: https://reviews.llvm.org/D53844
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@345832 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed