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| author | Sanjay Patel <spatel@rotateright.com> | 2017-01-20 22:18:47 +0000 |
|---|---|---|
| committer | Sanjay Patel <spatel@rotateright.com> | 2017-01-20 22:18:47 +0000 |
| commit | 0c1c70aef4a1d97188fde20e894bafeccd64224c (patch) | |
| tree | 93df8c022e8f943244b21ba8e5bf5784b2f5da7a /llvm/lib/LTO/LTOBackend.cpp | |
| parent | 867be0d14ce393108d848bcd9d080a92ca6b0006 (diff) | |
| download | bcm5719-llvm-0c1c70aef4a1d97188fde20e894bafeccd64224c.tar.gz bcm5719-llvm-0c1c70aef4a1d97188fde20e894bafeccd64224c.zip | |
[ValueTracking] recognize variations of 'clamp' to improve codegen (PR31693)
By enhancing value tracking, we allow an existing min/max canonicalization to
kick in and improve codegen for several targets that have min/max instructions.
Unfortunately, recognizing min/max in value tracking may cause us to hit
a hack in InstCombiner::visitICmpInst() more often:
http://lists.llvm.org/pipermail/llvm-dev/2017-January/109340.html
...but I'm hoping we can remove that soon.
Correctness proofs based on Alive:
Name: smaxmin
Pre: C1 < C2
%cmp2 = icmp slt i8 %x, C2
%min = select i1 %cmp2, i8 %x, i8 C2
%cmp3 = icmp slt i8 %x, C1
%r = select i1 %cmp3, i8 C1, i8 %min
=>
%cmp2 = icmp slt i8 %x, C2
%min = select i1 %cmp2, i8 %x, i8 C2
%cmp1 = icmp sgt i8 %min, C1
%r = select i1 %cmp1, i8 %min, i8 C1
Name: sminmax
Pre: C1 > C2
%cmp2 = icmp sgt i8 %x, C2
%max = select i1 %cmp2, i8 %x, i8 C2
%cmp3 = icmp sgt i8 %x, C1
%r = select i1 %cmp3, i8 C1, i8 %max
=>
%cmp2 = icmp sgt i8 %x, C2
%max = select i1 %cmp2, i8 %x, i8 C2
%cmp1 = icmp slt i8 %max, C1
%r = select i1 %cmp1, i8 %max, i8 C1
----------------------------------------
Optimization: smaxmin
Done: 1
Optimization is correct!
----------------------------------------
Optimization: sminmax
Done: 1
Optimization is correct!
Name: umaxmin
Pre: C1 u< C2
%cmp2 = icmp ult i8 %x, C2
%min = select i1 %cmp2, i8 %x, i8 C2
%cmp3 = icmp ult i8 %x, C1
%r = select i1 %cmp3, i8 C1, i8 %min
=>
%cmp2 = icmp ult i8 %x, C2
%min = select i1 %cmp2, i8 %x, i8 C2
%cmp1 = icmp ugt i8 %min, C1
%r = select i1 %cmp1, i8 %min, i8 C1
Name: uminmax
Pre: C1 u> C2
%cmp2 = icmp ugt i8 %x, C2
%max = select i1 %cmp2, i8 %x, i8 C2
%cmp3 = icmp ugt i8 %x, C1
%r = select i1 %cmp3, i8 C1, i8 %max
=>
%cmp2 = icmp ugt i8 %x, C2
%max = select i1 %cmp2, i8 %x, i8 C2
%cmp1 = icmp ult i8 %max, C1
%r = select i1 %cmp1, i8 %max, i8 C1
----------------------------------------
Optimization: umaxmin
Done: 1
Optimization is correct!
----------------------------------------
Optimization: uminmax
Done: 1
Optimization is correct!
llvm-svn: 292660
Diffstat (limited to 'llvm/lib/LTO/LTOBackend.cpp')
0 files changed, 0 insertions, 0 deletions
