S390:[crankshaft] Sign-ext key before array access

src/s390/macro-assembler-s390.h

Index: src/s390/macro-assembler-s390.h
diff --git a/src/s390/macro-assembler-s390.h b/src/s390/macro-assembler-s390.h
index 09310c5ea6248c577e776f54fe35d5bf45d78d89..5b38e30a0dfb3a53fa6c8b55cca6e14e89644818 100644
--- a/src/s390/macro-assembler-s390.h
+++ b/src/s390/macro-assembler-s390.h
@@ -1588,6 +1588,12 @@ class MacroAssembler : public Assembler {
     if (isSmi) {
       SmiToArrayOffset(dst, src, elementSizeLog2);
     } else {
+#if V8_TARGET_ARCH_S390X
+      // src (key) is a 32-bit integer.  Sign extension ensures
+      // upper 32-bit does not contain garbage before being used to
+      // reference memory.
+      lgfr(src, src);
+#endif
       ShiftLeftP(dst, src, Operand(elementSizeLog2));
     }
   }