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Author SHA1 Message Date
Sanjay Patel 79e7f6b3e3 [InstCombine] narrow lshr with constant 
Name: narrow_shift
Pre: C1 < 8
%zx = zext i8 %x to i32
%l = lshr i32 %zx, C1
  =>  
%narrowC = trunc i32 C1 to i8
%ns = lshr i8 %x, %narrowC
%l = zext i8 %ns to i32

http://rise4fun.com/Alive/jIV

This isn't directly applicable to PR34046 as written, but we
need to have more narrowing folds like this to be sure that
rotate patterns are recognized.

llvm-svn: 310060
 2017-08-04 15:42:47 +00:00
Sanjay Patel 2e33bbaff0 [InstCombine] lshr (sext iM X to iN), N-M --> zext (ashr X, min(N-M, M-1)) to iN 
This is a follow-up to https://reviews.llvm.org/D33879 / https://reviews.llvm.org/rL304939 ,
and was discussed in https://reviews.llvm.org/D33338.

We prefer this form because a narrower shift may be cheaper, and we can more easily fold a
zext than a sext.

http://rise4fun.com/Alive/slVe

Name: shz
%s = sext i8 %x to i12
%r = lshr i12 %s, 4
=>
%a = ashr i8 %x, 4
%r = zext i8 %a to i12 

llvm-svn: 305190
 2017-06-12 14:23:43 +00:00
Sanjay Patel 66f7fdb300 [InstCombine] fold lshr (sext X), C1 --> zext (lshr X, C2) 
This was discussed in D33338. We have larger pattern-matching ending in a truncate that 
we can reduce or remove by handling these smaller patterns first. Further motivation is 
that narrower shift ops are easier for value tracking and zext is better than sext.

http://rise4fun.com/Alive/rhh

Name: boolshift
%sext = sext i1 %x to i8
%r = lshr i8 %sext, 7

=>

%r = zext i1 %x to i8

Name: noboolshift
%sext = sext i3 %x to i8
%r = lshr i8 %sext, 7

=>

%sh = lshr i3 %x, 2
%r = zext i3 %sh to i8

Differential Revision: https://reviews.llvm.org/D33879

llvm-svn: 304939
 2017-06-07 20:32:08 +00:00
Sanjay Patel 7d383d6a69 [InstCombine] add tests for potential (lshr(sext X), C) folds; NFC 
As discussed in:
https://reviews.llvm.org/D33338
...we may be able to remove a wider pattern match by doing these more
basic canonicalizations.

llvm-svn: 303504
 2017-05-21 15:18:52 +00:00
Sanjay Patel 2d4b456427 [InstCombine] use m_APInt to allow lshr folds for vectors with splat constants 
llvm-svn: 291972
 2017-01-13 23:04:10 +00:00
Sanjay Patel d511dde2ec [InstCombine / InstSimplify] add and move tests for lshr transforms; NFC 
llvm-svn: 291970
 2017-01-13 22:54:12 +00:00