[PATCH] support llvm.vectorization.vector_width metadata

[罗勇刚(Yonggang Luo)]

lgtm, full featured and implemented cleanly.
在 2013-5-29 上午1:59，"Redmond, Paul" <paul.redmond at intel.com>写道：

> Hi,
>
> Attached is a new patch.
>
> - use width=1 instead of already_vectorized/disabled
> - removed disabled
> - attempted to make documentation for llvm.vectorizer.width more clear
> - check unroll and width are powers of two and unroll <= 16 and width <= 64
> - addressed style issues
>
> paul
>
>
>
> On 2013-05-27, at 3:57 PM, Nadav Rotem wrote:
>
> HI Paul,
>
> Thanks for working on this. This patch LGTM with one comment and a few nit
> picking.
>
> +    LoopVectorizeHints Hints(L);
> +
> +    if (Hints.AlreadyVectorized) {
> +      DEBUG(dbgs() << "LV: This loop was vectorized before\n");
> +      return false;
> +    }
> +    if (Hints.Disable) {
> +      DEBUG(dbgs() << "LV: Not vectorizing (disabled).\n");
> +      return false;
> +    }
> +
>
>  Why do we need both “Disable Vectorization” and “Already Vectorized” ? I
> think that we can merge them into one name.
>
>
> +MDNode *Loop::getLoopID() const {
> +  MDNode *LoopID = 0;
> +  if (isLoopSimplifyForm()) {
> +    LoopID = getLoopLatch()->getTerminator()->getMetadata("llvm.loop");
> +  } else {
> +    // Go through each predecessor of the loop header and check the
> +    // terminator for the metadata.
> +    BasicBlock *H = getHeader();
> +    for (block_iterator I = block_begin(), IE = block_end(); I != IE;
> ++I) {
>
> Why are you not using the Latch block ? Is it because of rotated loops ?
>
> +    getLoopLatch()->getTerminator()->setMetadata("llvm.loop", LoopID);
>
> Can you save the constant “llvm.loop” in a static variable ?
>
> +  /// Mark the loop L as already vectorized using the already_vectozed
> hint.
> +  void setAlreadyVectorized(Loop *L) {
> +    assert(!AlreadyVectorized);
>
> Assertions should have a string to describe the error.
>
> +    if (LoopID) {
> +      for (unsigned i = 1, ie = LoopID->getNumOperands(); i < ie; ++i)
> +        Vals.push_back(LoopID->getOperand(i));
> +    }
>
> No need for braces.
>
> +
> +    // First operand should refer to the loop id itself.
> +    assert(LoopID->getNumOperands() > 0);
> +    assert(LoopID->getOperand(0) == LoopID);
>
> Asserts need to have strings.
>
> +  // Check string hint with one operand.
> +  void getHint(StringRef Hint, Value *Arg) {
> +    if (Hint == "width") {
> +      const ConstantInt *C = dyn_cast<ConstantInt>(Arg);
> +      Width = C ? C->getZExtValue() : Width;
> +    } else if (Hint == "unroll") {
> +      const ConstantInt *C = dyn_cast<ConstantInt>(Arg);
> +      Unroll = C ? C->getZExtValue() : Unroll;
> +    }
> +  }
> +};
>
>
> Can you verify that the values of unroll and width are reasonable ? Such
> as power of two, smaller than 128, etc.
>
>
> Did you decide to call it ‘llvm.vectorizer’ or ‘llvm.vectorize’ ? I am
> okay with either one.
>
>
> Thanks,
> Nadav
>
> On May 27, 2013, at 12:42 PM, "Redmond, Paul" <paul.redmond at intel.com
> <mailto:paul.redmond at intel.com>> wrote:
>
> Attached is an updated patch that:
>
> - documents llvm.vectorizer.* metadata
> - documents llvm.loop and updates llvm.mem.parallel_loop_access
> - moves loop vectorizer metadata handling into utility class
> LoopVectorizerHints
> - moves getting/setting of llvm.vectorizer.already_vectorized into
> LoopVectorizerHints
> - adds support for llvm.vectorizer.width, llvm.vectorizer.unroll, and
> llvm.vectorizer.disable
>  - llvm.vectorizer.force and llvm.vectorizer.max_iterations will be
> addressed later.
> - updated tests
>
> paul
>
>
> On 2013-05-24, at 2:07 PM, Nadav Rotem wrote:
>
> Hi Paul,
>
> Thanks for working on this.  Can you also refactor the code that sets
> metadata on vectorized loops (so that they are not re-vectorized) ?
>
>
> -bool Loop::isAnnotatedParallel() const {
> +MDNode *Loop::getLoopID() const {
> +  MDNode *LoopID = 0;
>
> Please add braces below.
>
> +  if (isLoopSimplifyForm())
> +    LoopID = getLoopLatch()->getTerminator()->getMetadata("llvm.loop");
> +  else {
> +    // Go through each predecessor of the loop header and check the
> +    // terminator for the metadata.
> +    BasicBlock *H
>
>
> Please add a string for the asserts below.
>
> +void Loop::setLoopID(MDNode *LoopID) const {
> +  assert(LoopID);
> +  assert(LoopID->getNumOperands() > 0);
> +  assert(LoopID->getOperand(0) == LoopID);
>
>
> Can you outline the code below to a function and use it around the code
> that checks for the command line flags ?
>
> +    unsigned UserVF = VectorizationFactor;
> +
> +    // Check the loop metadata for vectorization hints.
> +    if (const MDNode *LoopID = L->getLoopID()) {
> +      assert(LoopID->getNumOperands() > 0);
> +      assert(LoopID->getOperand(0) == LoopID);
> +      for (unsigned i = 1, ie = LoopID->getNumOperands(); i < ie; ++i) {
> +        const MDNode *MD = dyn_cast<MDNode>(LoopID->getOperand(i));
> +        if (!MD)
> +          continue;
>
> Use early exits (continue) here:
>
> +        if (MD->getNumOperands() == 2) {
> +          if (const MDString *S = dyn_cast<MDString>(MD->getOperand(0))) {
> +            if (S->getString() == "llvm.vectorization.vector_width") {
> +              const ConstantInt *C =
> dyn_cast<ConstantInt>(MD->getOperand(1));
> +              UserVF = C ? C->getZExtValue() : UserVF;
>
>
> Because of this:
>
> +            }
> +          }
> +        }
> +      }
> +    }
> +
>
>
> Thanks,
> Nadav
>
>
> On May 24, 2013, at 10:49 AM, "Redmond, Paul" <paul.redmond at intel.com
> <mailto:paul.redmond at intel.com><mailto:paul.redmond at intel.com>> wrote:
>
> Hi,
>
> The attached patch modifies LoopVectorizer to recognize
> llvm.vectorization.vector_width metadata attached to llvm.loop metadata.
>
> The llvm.loop.parallel metadata has been renamed to llvm.loop to be more
> generic. Loop::isAnnotatedParallel now looks for llvm.loop and associated
> llvm.mem.parallel_loop_access. If we decide that we still need an explicit
> llvm.loop.parallel metadata then it can be added as a child of llvm.loop.
>
> Loop::setLoopID was added for symmetry and it is used in a forthcoming
> patch which preserves llvm.loop metadata in loop passes.
>
> paul
>
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