The matchSelectPattern code can match patterns like (x >= 0) ? x : -x
for absolute value. But it can also match ((x-y) >= 0) ? (x-y) : (y-x).
If the latter form was matched we can only use the nsw flag if its
set on both subtracts.
This match makes sure we're looking at the former case only.
Differential Revision: https://reviews.llvm.org/D65692
llvm-svn: 368195
computeKnownBits will indicate the sign bit of abs is 0 if the
the RHS operand returned by matchSelectPattern has the nsw flag set.
For abs idioms like (X >= 0) ? X : -X, the RHS returns -X. But
we can also match ((X-Y) >= 0 ? X-Y : Y-X as abs. In this case
RHS will be the Y-X operand. According to Alive, the sign bit for
this is only 0 if both the X-Y and Y-X operands have the nsw flag.
But we're only checking the Y-X operand.
llvm-svn: 367747
As it's causing some bot failures (and per request from kbarton).
This reverts commit r358543/ab70da07286e618016e78247e4a24fcb84077fda.
llvm-svn: 358546
This is a small followup to D59511. The code that was moved into
computeConstantRange() there is a bit overly conversative: If the
abs is not nsw, it does not compute any range. However, abs without
nsw still has a well-defined contiguous unsigned range from 0 to
SIGNED_MIN. This is a lot less useful than the usual 0 to SIGNED_MAX
range, but if we're already here we might as well specify it...
Differential Revision: https://reviews.llvm.org/D59563
llvm-svn: 356586
Craig Topper