maxjhandsome
/
llvm-project
forked from OSchip/llvm-project
1
0
Fork 0
Code Issues Pull Requests Packages Releases Wiki Activity
273,232 Commits 23 Branches 0 Tags 2.2 GiB
C++ 39.1%
LLVM 35.7%
C 12.1%
Assembly 8.9%
Python 1.1%
Other 2.7%
Go to file
Sanjay Patel 7ac2db6a48 [InstCombine] improve folds for icmp gt/lt (shr X, C1), C2 
We can always eliminate the shift in: icmp gt/lt (shr X, C1), C2 --> icmp gt/lt X, C'
This patch was supposed to just be an efficiency improvement because we were doing this 3-step process to fold:

IC: Visiting:   %c = icmp ugt i4 %s, 1
IC: ADD:   %s = lshr i4 %x, 1
IC: ADD:   %1 = udiv i4 %x, 2
IC: Old =   %c = icmp ugt i4 %1, 1
    New =   <badref> = icmp uge i4 %x, 4
IC: ADD:   %c = icmp uge i4 %x, 4
IC: ERASE   %2 = icmp ugt i4 %1, 1
IC: Visiting:   %c = icmp uge i4 %x, 4
IC: Old =   %c = icmp uge i4 %x, 4
    New =   <badref> = icmp ugt i4 %x, 3
IC: ADD:   %c = icmp ugt i4 %x, 3
IC: ERASE   %2 = icmp uge i4 %x, 4
IC: Visiting:   %c = icmp ugt i4 %x, 3
IC: DCE:   %1 = udiv i4 %x, 2
IC: ERASE   %1 = udiv i4 %x, 2
IC: DCE:   %s = lshr i4 %x, 1
IC: ERASE   %s = lshr i4 %x, 1
IC: Visiting:   ret i1 %c

When we could go directly to canonical icmp form:

IC: Visiting:   %c = icmp ugt i4 %s, 1
IC: Old =   %c = icmp ugt i4 %s, 1
    New =   <badref> = icmp ugt i4 %x, 3
IC: ADD:   %c = icmp ugt i4 %x, 3
IC: ERASE   %1 = icmp ugt i4 %s, 1
IC: ADD:   %s = lshr i4 %x, 1
IC: DCE:   %s = lshr i4 %x, 1
IC: ERASE   %s = lshr i4 %x, 1
IC: Visiting:   %c = icmp ugt i4 %x, 3

...but then I noticed that the folds were incomplete too:
https://godbolt.org/g/aB2hLE

Here are attempts to prove the logic with Alive:
https://rise4fun.com/Alive/92o

Name: lshr_ult
Pre: ((C2 << C1) u>> C1) == C2
%sh = lshr i8 %x, C1
%r = icmp ult i8 %sh, C2
  =>
%r = icmp ult i8 %x, (C2 << C1)

Name: ashr_slt
Pre: ((C2 << C1) >> C1) == C2
%sh = ashr i8 %x, C1
%r = icmp slt i8 %sh, C2
  =>
%r = icmp slt i8 %x, (C2 << C1)

Name: lshr_ugt
Pre: (((C2+1) << C1) u>> C1) == (C2+1)
%sh = lshr i8 %x, C1
%r = icmp ugt i8 %sh, C2
  =>
%r = icmp ugt i8 %x, ((C2+1) << C1) - 1

Name: ashr_sgt
Pre: (C2 != 127) && ((C2+1) << C1 != -128) && (((C2+1) << C1) >> C1) == (C2+1)
%sh = ashr i8 %x, C1
%r = icmp sgt i8 %sh, C2
  =>
%r = icmp sgt i8 %x, ((C2+1) << C1) - 1

Name: ashr_exact_sgt
Pre: ((C2 << C1) >> C1) == C2
%sh = ashr exact i8 %x, C1
%r = icmp sgt i8 %sh, C2
  =>
%r = icmp sgt i8 %x, (C2 << C1)

Name: ashr_exact_slt
Pre: ((C2 << C1) >> C1) == C2
%sh = ashr exact i8 %x, C1
%r = icmp slt i8 %sh, C2
  =>
%r = icmp slt i8 %x, (C2 << C1)

Name: lshr_exact_ugt
Pre: ((C2 << C1) u>> C1) == C2
%sh = lshr exact i8 %x, C1
%r = icmp ugt i8 %sh, C2
  =>
%r = icmp ugt i8 %x, (C2 << C1)

Name: lshr_exact_ult
Pre: ((C2 << C1) u>> C1) == C2
%sh = lshr exact i8 %x, C1
%r = icmp ult i8 %sh, C2
  =>
%r = icmp ult i8 %x, (C2 << C1)

We did something similar for 'shl' in D28406.

Differential Revision: https://reviews.llvm.org/D38514

llvm-svn: 315021
 		2017-10-05 21:11:49 +00:00
clang Cleanup and generalize -shared-libasan. 2017-10-05 20:14:00 +00:00
clang-tools-extra [clangd] Added async API to run code completion. 2017-10-05 17:04:13 +00:00
compiler-rt [asan] Add --enable-new-dtags in tests on Android. 2017-10-05 20:45:12 +00:00
debuginfo-tests Revert r313600 due to bot failures on Green Dragon. 2017-09-19 14:51:37 +00:00
libclc configure: Fix handling of directories with compats only source lists 2017-10-05 20:16:28 +00:00
libcxx [libc++] Clarify names of ABI forcing macros 2017-10-05 02:18:08 +00:00
libcxxabi Fix ASAN build with older compiler-rt versions. 2017-09-14 22:37:34 +00:00
libunwind build: use POSITION_INDEPENDENT_CODE instead of -fPIC 2017-10-03 20:22:26 +00:00
lld Remove dead code. 2017-10-05 03:01:05 +00:00
lldb Enable breakpoints and read/write GPRs for ppc64le 2017-10-05 19:44:05 +00:00
llgo irgen: Create functions instead of global variables for builtin hash and equal algorithms. 2017-06-04 22:11:28 +00:00
llvm [InstCombine] improve folds for icmp gt/lt (shr X, C1), C2 2017-10-05 21:11:49 +00:00
openmp [test] Fix uninitialized memory in omp_taskloop_grainsize.c 2017-09-29 13:53:03 +00:00
parallel-libs [Axccel] Remove -Wno-missing-braces in build 2016-12-19 21:34:07 +00:00
polly [ScopBuilder] Introduce -polly-stmt-granularity=scalar-indep option. 2017-10-05 13:43:00 +00:00