[llvm] r364207 - [X86] Don't a vzext_movl in LowerBuildVectorv16i8/LowerBuildVectorv8i16 if there are no zeroes in the vector we're building.

[Craig Topper via llvm-commits]

Author: ctopper
Date: Mon Jun 24 10:28:41 2019
New Revision: 364207

URL: http://llvm.org/viewvc/llvm-project?rev=364207&view=rev
Log:
[X86] Don't a vzext_movl in LowerBuildVectorv16i8/LowerBuildVectorv8i16 if there are no zeroes in the vector we're building.

In LowerBuildVectorv16i8 we took care to use an any_extend if the first pair is in the lower 16-bits of the vector and no elements are 0. So bits [31:16] will be undefined. But we still emitted a vzext_movl to ensure that bits [127:32] are 0. If we don't need any zeroes we should be consistent and make all of 127:16 undefined.

In LowerBuildVectorv8i16 we can just delete the vzext_movl code because we only use the scalar_to_vector when there are no zeroes. So the vzext_movl is always unnecessary.

Found while investigating whether (vzext_movl (scalar_to_vector (loadi32)) patterns are necessary. At least one of the cases where they were necessary was where the loadi32 matched 32-bit aligned 16-bit extload. Seemed weird that we required vzext_movl for that case.

Differential Revision: https://reviews.llvm.org/D63700

Modified:
    llvm/trunk/lib/Target/X86/X86ISelLowering.cpp

Modified: llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86ISelLowering.cpp?rev=364207&r1=364206&r2=364207&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86ISelLowering.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86ISelLowering.cpp Mon Jun 24 10:28:41 2019
@@ -7112,7 +7112,7 @@ static SDValue LowerBuildVectorAsInsert(
 
     // If the build vector contains zeros or our first insertion is not the
     // first index then insert into zero vector to break any register
-    // dependency else use SCALAR_TO_VECTOR/VZEXT_MOVL.
+    // dependency else use SCALAR_TO_VECTOR.
     if (First) {
       First = false;
       if (NumZero || 0 != i)
@@ -7121,7 +7121,6 @@ static SDValue LowerBuildVectorAsInsert(
         assert(0 == i && "Expected insertion into zero-index");
         V = DAG.getAnyExtOrTrunc(Op.getOperand(i), dl, MVT::i32);
         V = DAG.getNode(ISD::SCALAR_TO_VECTOR, dl, MVT::v4i32, V);
-        V = DAG.getNode(X86ISD::VZEXT_MOVL, dl, MVT::v4i32, V);
         V = DAG.getBitcast(VT, V);
         continue;
       }
@@ -7184,7 +7183,8 @@ static SDValue LowerBuildVectorv16i8(SDV
           V = NumZero ? DAG.getZExtOrTrunc(ThisElt, dl, MVT::i32)
                       : DAG.getAnyExtOrTrunc(ThisElt, dl, MVT::i32);
           V = DAG.getNode(ISD::SCALAR_TO_VECTOR, dl, MVT::v4i32, V);
-          V = DAG.getNode(X86ISD::VZEXT_MOVL, dl, MVT::v4i32, V);
+          if (NumZero)
+            V = DAG.getNode(X86ISD::VZEXT_MOVL, dl, MVT::v4i32, V);
           V = DAG.getBitcast(MVT::v8i16, V);
         } else {
           V = DAG.getNode(ISD::INSERT_VECTOR_ELT, dl, MVT::v8i16, V, ThisElt,