[DagCombiner] Not all 'andn''s work with immediates.

Summary:
Split off from D46031.

In masked merge case, this degrades IPC by decreasing instruction count.
{F6108777}
The next patch should be able to recover and improve this.

This also affects the transform @spatel have added in D27489 / rL289738,
and the test coverage for X86 was missing.
But after i have added it, and looked at the changes in MCA, i'm somewhat confused.
{F6093591} {F6093592} {F6093593}
I'd say this regression is an improvement, since `IPC` increased in that case?

Reviewers: spatel, craig.topper

Reviewed By: spatel

Subscribers: andreadb, llvm-commits, spatel

Differential Revision: https://reviews.llvm.org/D46493

llvm-svn: 331684

1 files changed, 4 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 322e9be0083..b809bbc1c6c 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -5428,6 +5428,10 @@ SDValue DAGCombiner::unfoldMaskedMerge(SDNode *N) {
   if (!TLI.hasAndNot(M))
     return SDValue();
 
+  // If Y is a constant, check that 'andn' works with immediates.
+  if (!TLI.hasAndNot(Y))
+    return SDValue();
+
   SDLoc DL(N);
 
   SDValue LHS = DAG.getNode(ISD::AND, DL, VT, X, M);