[X86] Rework the logic in LowerBuildVectorv16i8 to make better use of any_extend and break false dependencies. Other improvements

This patch rewrites the loop iteration to only visit every other element starting with element 0. And we work on the "even" element and "next" element at the same time. The "First" logic has been moved to the bottom of the loop and doesn't run on every element. I believe it could create dangling nodes previously since we didn't check if we were going to use SCALAR_TO_VECTOR for the first insertion. I got rid of the "First" variable and just do a null check on V which should be equivalent. We also no longer use undef as the starting V for vectors with no zeroes to avoid false dependencies. This matches v8i16.

I've changed all the extends and OR operations to use MVT::i32 since that's what they'll be promoted to anyway. I've tried to use zero_extend only when necessary and use any_extend otherwise. This resulted in some improvements in tests where we are now able to promote aligned (i32 (extload i8)) to a 32-bit load.

Differential Revision: https://reviews.llvm.org/D63702

llvm-svn: 364469

1 files changed, 37 insertions, 37 deletions

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 21bb426fcfe..4557c0a1f54 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -7175,51 +7175,51 @@ static SDValue LowerBuildVectorv16i8(SDValue Op, unsigned NonZeros,
 
   SDLoc dl(Op);
   SDValue V;
-  bool First = true;
 
   // Pre-SSE4.1 - merge byte pairs and insert with PINSRW.
-  for (unsigned i = 0; i < 16; ++i) {
+  for (unsigned i = 0; i < 16; i += 2) {
     bool ThisIsNonZero = (NonZeros & (1 << i)) != 0;
-    if (ThisIsNonZero && First) {
-      if (NumZero)
-        V = getZeroVector(MVT::v8i16, Subtarget, DAG, dl);
+    bool NextIsNonZero = (NonZeros & (1 << (i + 1))) != 0;
+    if (!ThisIsNonZero && !NextIsNonZero)
+      continue;
+
+    // FIXME: Investigate combining the first 4 bytes as a i32 instead.
+    SDValue Elt;
+    if (ThisIsNonZero) {
+      if (NumZero || NextIsNonZero)
+        Elt = DAG.getZExtOrTrunc(Op.getOperand(i), dl, MVT::i32);
       else
-        V = DAG.getUNDEF(MVT::v8i16);
-      First = false;
+        Elt = DAG.getAnyExtOrTrunc(Op.getOperand(i), dl, MVT::i32);
     }
 
-    if ((i & 1) != 0) {
-      // FIXME: Investigate extending to i32 instead of just i16.
-      // FIXME: Investigate combining the first 4 bytes as a i32 instead.
-      SDValue ThisElt, LastElt;
-      bool LastIsNonZero = (NonZeros & (1 << (i - 1))) != 0;
-      if (LastIsNonZero) {
-        LastElt =
-            DAG.getNode(ISD::ZERO_EXTEND, dl, MVT::i16, Op.getOperand(i - 1));
-      }
-      if (ThisIsNonZero) {
-        ThisElt = DAG.getNode(ISD::ZERO_EXTEND, dl, MVT::i16, Op.getOperand(i));
-        ThisElt = DAG.getNode(ISD::SHL, dl, MVT::i16, ThisElt,
-                              DAG.getConstant(8, dl, MVT::i8));
-        if (LastIsNonZero)
-          ThisElt = DAG.getNode(ISD::OR, dl, MVT::i16, ThisElt, LastElt);
-      } else
-        ThisElt = LastElt;
-
-      if (ThisElt) {
-        if (1 == i) {
-          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);
-          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,
-                          DAG.getIntPtrConstant(i / 2, dl));
-        }
+    if (NextIsNonZero) {
+      SDValue NextElt;
+      if (i == 0 && NumZero)
+        NextElt = DAG.getZExtOrTrunc(Op.getOperand(i+1), dl, MVT::i32);
+      else
+        NextElt = DAG.getAnyExtOrTrunc(Op.getOperand(i+1), dl, MVT::i32);
+      NextElt = DAG.getNode(ISD::SHL, dl, MVT::i32, NextElt,
+                            DAG.getConstant(8, dl, MVT::i8));
+      if (ThisIsNonZero)
+        Elt = DAG.getNode(ISD::OR, dl, MVT::i32, NextElt, Elt);
+      else
+        Elt = NextElt;
+    }
+
+    // If our first insertion is not the first index then insert into zero
+    // vector to break any register dependency else use SCALAR_TO_VECTOR.
+    if (!V) {
+      if (i != 0)
+        V = getZeroVector(MVT::v8i16, Subtarget, DAG, dl);
+      else {
+        V = DAG.getNode(ISD::SCALAR_TO_VECTOR, dl, MVT::v4i32, Elt);
+        V = DAG.getBitcast(MVT::v8i16, V);
+        continue;
       }
     }
+    Elt = DAG.getNode(ISD::TRUNCATE, dl, MVT::i16, Elt);
+    V = DAG.getNode(ISD::INSERT_VECTOR_ELT, dl, MVT::v8i16, V, Elt,
+                    DAG.getIntPtrConstant(i / 2, dl));
   }
 
   return DAG.getBitcast(MVT::v16i8, V);