[llvm] [VPlan] Enable vectorization of early-exit loops with unit-stride fault-only-first loads (PR #151300)

[Raphael Moreira Zinsly via llvm-commits]

rzinsly wrote:

Hi, I wanted to try this patch but the new test is failing for a Release build:

```
******************** TEST 'LLVM :: Transforms/LoopVectorize/RISCV/find.ll' FAILED ********************
Exit Code: 2

Command Output (stdout):
--
# RUN: at line 2
/home/rzinsly/build/llvm/bin/opt -passes=loop-vectorize -enable-early-exit-with-ffload -mtriple=riscv64 -mattr=+v -S /home/rzinsly/src/llvm-project/llvm/test/Transforms/LoopVectorize/RISCV/find.ll | /home/rzinsly/build/llvm/bin/FileCheck /home/rzinsly/src/llvm-project/llvm/test/Transforms/LoopVectorize/RISCV/find.ll
# executed command: /home/rzinsly/build/llvm/bin/opt -passes=loop-vectorize -enable-early-exit-with-ffload -mtriple=riscv64 -mattr=+v -S /home/rzinsly/src/llvm-project/llvm/test/Transforms/LoopVectorize/RISCV/find.ll
# .---command stderr------------
# | PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace and instructions to reproduce the bug.
# | Stack dump:
# | 0.  Program arguments: /home/rzinsly/build/llvm/bin/opt -passes=loop-vectorize -enable-early-exit-with-ffload -mtriple=riscv64 -mattr=+v -S /home/rzinsly/src/llvm-project/llvm/test/Transforms/LoopVectorize/RISCV/find.ll
# | 1.  Running pass "function(loop-vectorize<no-interleave-forced-only;no-vectorize-forced-only;>)" on module "/home/rzinsly/src/llvm-project/llvm/test/Transforms/LoopVectorize/RISCV/find.ll"
# | 2.  Running pass "loop-vectorize<no-interleave-forced-only;no-vectorize-forced-only;>" on function "find_with_liveout"
# |  #0 0x00005a92b002fe62 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/home/rzinsly/build/llvm/bin/opt+0x2f67e62)
# |  #1 0x00005a92b002cda2 SignalHandler(int, siginfo_t*, void*) Signals.cpp:0:0
# |  #2 0x0000736eee245330 (/lib/x86_64-linux-gnu/libc.so.6+0x45330)
# |  #3 0x00005a92ae0d7df4 llvm::VPValue::getDefiningRecipe() (/home/rzinsly/build/llvm/bin/opt+0x100fdf4)
# |  #4 0x00005a92ae1436c8 llvm::VPlanTransforms::adjustFFLoadEarlyExitForPoisonSafety(llvm::VPlan&) (/home/rzinsly/build/llvm/bin/opt+0x107b6c8)
# |  #5 0x00005a92adf8422a llvm::LoopVectorizationPlanner::tryToBuildVPlanWithVPRecipes(std::unique_ptr<llvm::VPlan, std::default_delete<llvm::VPlan>>, llvm::VFRange&, llvm::LoopVersioning*) (/home/rzinsly/build/llvm/bin/opt+0xebc22a)
# |  #6 0x00005a92adf85c79 llvm::LoopVectorizationPlanner::buildVPlansWithVPRecipes(llvm::ElementCount, llvm::ElementCount) (/home/rzinsly/build/llvm/bin/opt+0xebdc79)
# |  #7 0x00005a92adf861bd llvm::LoopVectorizationPlanner::plan(llvm::ElementCount, unsigned int) (/home/rzinsly/build/llvm/bin/opt+0xebe1bd)
# |  #8 0x00005a92adf8bae4 llvm::LoopVectorizePass::processLoop(llvm::Loop*) (/home/rzinsly/build/llvm/bin/opt+0xec3ae4)
...
```

I’m building with:
`-DCMAKE_BUILD_TYPE=Release -DLLVM_TARGETS_TO_BUILD="RISCV" -DLLVM_ENABLE_PROJECTS="clang" -DLLVM_PARALLEL_LINK_JOBS=1 -DLLVM_OPTIMIZED_TABLEGEN=ON
`

It works with `-DCMAKE_BUILD_TYPE=Debug`.

https://github.com/llvm/llvm-project/pull/151300