[PATCH] D32245: Add an IR expansion pass for the experimental reductions

[Zhang Kang via Phabricator via llvm-commits]

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================
Comment at: llvm/trunk/include/llvm/Analysis/TargetTransformInfoImpl.h:466
+  bool shouldExpandReduction(const IntrinsicInst *II) const {
+    return true;
+  }
----------------
Hello @aemerson ,
Here you set the  function `shouldExpandReduction` to return true.
For below test case:
```asm
declare i8 @llvm.experimental.vector.reduce.and.i8.v3i8(<3 x i8> %a)
define i8 @test_v3i8(<3 x i8> %a) nounwind {
  %b = call i8 @llvm.experimental.vector.reduce.and.i8.v3i8(<3 x i8> %a)
  ret i8 %b
}
```

If I  built above case on ppc:, I will get below error:
```shell
llc error_case.ll -mtriple=powerpc64-unknown-linux-gnu
llc: /home/shkzhang/llvm/llvm/lib/Transforms/Utils/LoopUtils.cpp:828: llvm::Value *llvm::getShuffleReduction(IRBuilder<> &, llvm::Value *, unsigned int, RecurrenceDescriptor::MinMaxRecurrenceKind, ArrayRef<llvm::Value *>): Assertion `isPowerOf2_32(VF) && "Reduction emission only supported for pow2 vectors!"' failed.
Stack dump:
0.	Program arguments: llc error_case.ll -mtriple=powerpc64-unknown-linux-gnu
1.	Running pass 'Function Pass Manager' on module 'error_case.ll'.
2.	Running pass 'Expand reduction intrinsics' on function '@test_v3i8'
 #0 0x000000001244d094 PrintStackTraceSignalHandler(void*) (/home/shkzhang/llvm/build/bin/llc+0x1244d094)
 #1 0x000000001244a348 llvm::sys::RunSignalHandlers() (/home/shkzhang/llvm/build/bin/llc+0x1244a348)
 #2 0x000000001244d6cc SignalHandler(int) (/home/shkzhang/llvm/build/bin/llc+0x1244d6cc)
 #3 0x00007869689104d8 (linux-vdso64.so.1+0x4d8)
 #4 0x00007869681ee98c __libc_signal_restore_set /build/glibc-uvws04/glibc-2.27/signal/../sysdeps/unix/sysv/linux/nptl-signals.h:80:0
 #5 0x00007869681ee98c raise /build/glibc-uvws04/glibc-2.27/signal/../sysdeps/unix/sysv/linux/raise.c:48:0
 #6 0x00007869681f0be0 abort /build/glibc-uvws04/glibc-2.27/stdlib/abort.c:79:0
 #7 0x00007869681dbb38 __assert_fail_base /build/glibc-uvws04/glibc-2.27/assert/assert.c:92:0
 #8 0x00007869681dbbe4 __assert_fail /build/glibc-uvws04/glibc-2.27/assert/assert.c:101:0
 #9 0x00000000124e036c llvm::getShuffleReduction(llvm::IRBuilder<llvm::ConstantFolder, llvm::IRBuilderDefaultInserter>&, llvm::Value*, unsigned int, llvm::RecurrenceDescriptor::MinMaxRecurrenceKind, llvm::ArrayRef<llvm::Value*>) (/home/shkzhang/llvm/build/bin/llc+0x124e036c)
#10 0x000000001175de9c (anonymous namespace)::expandReductions(llvm::Function&, llvm::TargetTransformInfo const*) (/home/shkzhang/llvm/build/bin/llc+0x1175de9c)
#11 0x0000000011cc9700 llvm::FPPassManager::runOnFunction(llvm::Function&) (/home/shkzhang/llvm/build/bin/llc+0x11cc9700)
#12 0x0000000011cc9b90 llvm::FPPassManager::runOnModule(llvm::Module&) (/home/shkzhang/llvm/build/bin/llc+0x11cc9b90)
#13 0x0000000011cca354 llvm::legacy::PassManagerImpl::run(llvm::Module&) (/home/shkzhang/llvm/build/bin/llc+0x11cca354)
#14 0x0000000011cca9ec llvm::legacy::PassManager::run(llvm::Module&) (/home/shkzhang/llvm/build/bin/llc+0x11cca9ec)
#15 0x0000000010377408 compileModule(char**, llvm::LLVMContext&) (/home/shkzhang/llvm/build/bin/llc+0x10377408)
#16 0x0000000010374a3c main (/home/shkzhang/llvm/build/bin/llc+0x10374a3c)
#17 0x00007869681c441c generic_start_main /build/glibc-uvws04/glibc-2.27/csu/../csu/libc-start.c:310:0
#18 0x00007869681c4618 __libc_start_main /build/glibc-uvws04/glibc-2.27/csu/../sysdeps/unix/sysv/linux/powerpc/libc-start.c:116:0
Aborted (core dumped)
```

This is because I use `v3i8` here, it's not pow2. But for those ARCH like AArch64, this case can pass, because the function `shouldExpandReduction` will return false.

I have question that, whether we should fix above error. For example, if the number of element is not pow2, we do not call `shouldExpandReduction`?




Repository:
  rL LLVM

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  https://reviews.llvm.org/D32245/new/

https://reviews.llvm.org/D32245