[llvm] [SCEV] Fold (C1 * A /u C2) -> A /u (C2 /u C1), if C2 > C1. (PR #157656)

[Paul Kirth via llvm-commits]

ilovepi wrote:

We're seeing one of the msan tests fail after this patch: MemorySanitizer-AARCH64 :: preinit_array.cpp, and I've bisected the failure to this patch. I'm guessing the other failures are somewhat related. 

Bot: https://ci.chromium.org/ui/p/fuchsia/builders/toolchain.ci/clang-linux-arm64/b8704035006372869713/overview

Blame: https://ci.chromium.org/ui/p/fuchsia/builders/toolchain.ci/clang-linux-arm64/b8704035006372869713/blamelist

Logs: https://logs.chromium.org/logs/fuchsia/buildbucket/cr-buildbucket/8704035006372869713/+/u/clang/test/stdout

This is a normal aarch64 linux build of the toolchain and runtimes using the Fuchsia.cmake cache file. Its a pretty vanilla build otherwise.  The CMake can be found here: https://logs.chromium.org/logs/fuchsia/buildbucket/cr-buildbucket/8704035006372869713/+/u/clang/configure/l_execution_details

```
Command Output (stderr):
--
/b/s/w/ir/x/w/llvm_build/./bin/clang  --driver-mode=g++ -fsanitize=memory -mno-omit-leaf-frame-pointer -fno-omit-frame-pointer -fno-optimize-sibling-calls   -Wthread-safety -Wthread-safety-reference -Wthread-safety-beta   -gline-tables-only -O0 /b/s/w/ir/x/w/llvm-llvm-project/compiler-rt/test/msan/preinit_array.cpp -o /b/s/w/ir/x/w/llvm_build/runtimes/runtimes-aarch64-unknown-linux-gnu-bins/compiler-rt/test/msan/AARCH64/Output/preinit_array.cpp.tmp &&  /b/s/w/ir/x/w/llvm_build/runtimes/runtimes-aarch64-unknown-linux-gnu-bins/compiler-rt/test/msan/AARCH64/Output/preinit_array.cpp.tmp # RUN: at line 1
+ /b/s/w/ir/x/w/llvm_build/./bin/clang --driver-mode=g++ -fsanitize=memory -mno-omit-leaf-frame-pointer -fno-omit-frame-pointer -fno-optimize-sibling-calls -Wthread-safety -Wthread-safety-reference -Wthread-safety-beta -gline-tables-only -O0 /b/s/w/ir/x/w/llvm-llvm-project/compiler-rt/test/msan/preinit_array.cpp -o /b/s/w/ir/x/w/llvm_build/runtimes/runtimes-aarch64-unknown-linux-gnu-bins/compiler-rt/test/msan/AARCH64/Output/preinit_array.cpp.tmp
+ /b/s/w/ir/x/w/llvm_build/runtimes/runtimes-aarch64-unknown-linux-gnu-bins/compiler-rt/test/msan/AARCH64/Output/preinit_array.cpp.tmp
/b/s/w/ir/x/w/llvm_build/runtimes/runtimes-aarch64-unknown-linux-gnu-bins/compiler-rt/test/msan/AARCH64/Output/preinit_array.cpp.script: line 1: 1053327 Segmentation fault      /b/s/w/ir/x/w/llvm_build/runtimes/runtimes-aarch64-unknown-linux-gnu-bins/compiler-rt/test/msan/AARCH64/Output/preinit_array.cpp.tmp
```

https://github.com/llvm/llvm-project/pull/157656