llvm-project/llvm
Nicolai Haehnle a9cc92c247 AMDGPU: Fix various issues around the VirtReg2Value mapping
Summary:
The VirtReg2Value mapping is crucial for getting consistently
reliable divergence information into the SelectionDAG. This
patch fixes a bunch of issues that lead to incorrect divergence
info and introduces tight assertions to ensure we don't regress:

1. VirtReg2Value is generated lazily; there were some cases where
   a lookup was performed before all relevant virtual registers were
   created, leading to an out-of-sync mapping. Those cases were:

  - Complex code to lower formal arguments that generated CopyFromReg
    nodes from live-in registers (fixed by never querying the mapping
    for live-in registers).

  - Code that generates CopyToReg for formal arguments that are used
    outside the entry basic block (fixed by never querying the
    mapping for Register nodes, which don't need the divergence info
    anyway).

2. For complex values that are lowered to a sequence of registers,
   all registers must be reflected in the VirtReg2Value mapping.

I am not adding any new tests, since I'm not actually aware of any
bugs that these problems are causing with trunk as-is. However,
I recently added a test case (in r346423) which fails when D53283 is
applied without this change. Also, the new assertions should provide
most of the effective test coverage.

There is one test change in sdwa-peephole.ll. The underlying issue
is that since the divergence info is now correct, the DAGISel will
select V_OR_B32 directly instead of S_OR_B32. This leads to an extra
COPY which affects the behavior of MachineLICM in a way that ends up
with the S_MOV_B32 with the constant in a different basic block than
the V_OR_B32, which is presumably what defeats the peephole.

Reviewers: alex-t, arsenm, rampitec

Subscribers: kzhuravl, jvesely, wdng, yaxunl, dstuttard, tpr, t-tye, llvm-commits

Differential Revision: https://reviews.llvm.org/D54340

llvm-svn: 348049
2018-11-30 22:55:29 +00:00
..
benchmarks
bindings [bindings/go] Add Go bindings to LLVMGetIndices 2018-11-08 04:04:04 +00:00
cmake [CMake] build correctly if build path contains whitespace 2018-11-30 00:30:53 +00:00
docs [docs][AtomicExpandPass] Document the alternate lowering strategy for part-word atomicrmw/cmpxchg 2018-11-30 09:23:24 +00:00
examples Fix build break from r347239 2018-11-19 18:51:11 +00:00
include AMDGPU: Fix various issues around the VirtReg2Value mapping 2018-11-30 22:55:29 +00:00
lib AMDGPU: Fix various issues around the VirtReg2Value mapping 2018-11-30 22:55:29 +00:00
projects
resources
runtimes
test AMDGPU: Fix various issues around the VirtReg2Value mapping 2018-11-30 22:55:29 +00:00
tools [dsymutil] Gather global and local symbol addresses in the main executable. 2018-11-30 18:56:10 +00:00
unittests [ValueTracking] Make unit tests easier to write; NFC 2018-11-30 22:22:30 +00:00
utils [TableGen] Fix negation of simple predicates 2018-11-30 21:03:24 +00:00
.arcconfig
.clang-format
.clang-tidy
.gitattributes
.gitignore [git/svn] Ignore Visual Studio's CMakeSettings.json. 2018-10-29 14:51:02 +00:00
CMakeLists.txt [LLVM] Allow modulemap installation 2018-11-21 20:46:50 +00:00
CODE_OWNERS.TXT [CODE_OWNERS] Add myself as code owner for MinGW 2018-11-29 10:58:15 +00:00
CREDITS.TXT add Kang Zhang(shkzhang@cn.ibm.com) to the CREDITS.TXT 2018-11-25 02:56:49 +00:00
LICENSE.TXT
LLVMBuild.txt
README.txt
RELEASE_TESTERS.TXT Adding Yvan as release test backup for Diana 2018-11-08 11:51:27 +00:00
configure
llvm.spec.in

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