[PATCH] D49829: [X86] Add pattern matching for PMADDUBSW

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon added inline comments.


================
Comment at: lib/Target/X86/X86ISelLowering.cpp:36837
+  // is being performed:
+  //  A[2 * i] * B[2 * i] + A[2 * i + 1] * B[2 * i + 1]
+  SDValue ZExtIn, SExtIn;
----------------
craig.topper wrote:
> RKSimon wrote:
> > I always get nervous when we add vectorization detection in the DAG.
> Nervous how?
In this case it looks necessary, but it encourages the belief that its safe to perform vectorization in the DAG. In general we should be relying on the vectorizers to perform this using a proper cost analysis. see PR35732 as well.


https://reviews.llvm.org/D49829