[PATCH] LoopVectorizer: Don't attempt to vectorize extractelement instructions

[Arnold Schwaighofer]

You are disabling vectorization for any extractelement. Do they all not work or only the once with a vector operand? (I am not sure we care whether we vectorize code with extractelement for this to be important, I guess).

       // Check that the instruction return type is vectorizable.
-      if (!VectorType::isValidElementType(it->getType()) &&
-          !it->getType()->isVoidTy()) {
+      // Also, we can't vectorize extractelement instructions.
+      if ((!VectorType::isValidElementType(it->getType()) &&
+           !it->getType()->isVoidTy()) || isa<ExtractElementInst>(it)) {


I think if you specify a triple you must put the test in the targets subdirectory:

+++ b/test/Transforms/LoopVectorize/ee-crash.ll
@@ -0,0 +1,35 @@
+; RUN: opt < %s -loop-vectorize -force-vector-unroll=1 -force-vector-width=4 -S | FileCheck %s
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.8.0”

Otherwise, the test might fail when llvm is not compiled with x86_64 support.


Thanks,
Arnold

On Oct 25, 2013, at 3:13 PM, Hal Finkel <hfinkel at anl.gov> wrote:

> [With the patch this time].
> 
> ----- Original Message -----
>> Nadav, Arnold,
>> 
>> The loop vectorizer does not currently understand how to vectorize
>> extractelement instructions. The existing check, which excluded all
>> vector-valued instructions, did not catch extractelement instructions
>> because
>> it checked only the return value. As a result, vectorization would
>> proceed,
>> producing illegal instructions like this:
>> 
>>  %58 = extractelement <2 x i32> %15, i32 0
>>  %59 = extractelement i32 %58, i32 0
>> 
>> where the second extractelement is illegal because its first operand
>> is not a vector. Later passes (or the verifier) would then crash.
>> 
>> We could teach the vectorizer to handle this case when vectorizing,
>> but I think that might be a task better associated with a larger
>> effort in vectorizing vectorized loops. Please review.
>> 
>> Thanks again,
>> Hal
>> 
>> --
>> Hal Finkel
>> Assistant Computational Scientist
>> Leadership Computing Facility
>> Argonne National Laboratory
>> 
> 
> -- 
> Hal Finkel
> Assistant Computational Scientist
> Leadership Computing Facility
> Argonne National Laboratory
> <lv-ee-crash.patch>