[x64] 64-bit shift left by 32 or more covers sign/zero extend.

src/compiler/x64/instruction-selector-x64.cc

Index: src/compiler/x64/instruction-selector-x64.cc
diff --git a/src/compiler/x64/instruction-selector-x64.cc b/src/compiler/x64/instruction-selector-x64.cc
index f927501c6531e45ecfd6024e5545fca253846264..c70944bc86d085509da1b3cdb44305f4043212df 100644
--- a/src/compiler/x64/instruction-selector-x64.cc
+++ b/src/compiler/x64/instruction-selector-x64.cc
@@ -320,6 +320,17 @@ void InstructionSelector::VisitWord32Shl(Node* node) {
 
 
 void InstructionSelector::VisitWord64Shl(Node* node) {
+  X64OperandGenerator g(this);
+  Int64BinopMatcher m(node);
+  if ((m.left().IsChangeInt32ToInt64() || m.left().IsChangeUint32ToUint64()) &&
+      m.right().IsInRange(32, 63)) {
+    // There's no need to sign/zero-extend to 64-bit if we shift out the upper
+    // 32 bits anyway.
+    Emit(kX64Shl, g.DefineSameAsFirst(node),
+         g.UseRegister(m.left().node()->InputAt(0)),
+         g.UseImmediate(m.right().node()));
+    return;
+  }
   VisitWord64Shift(this, node, kX64Shl);
 }