Fix #2574: Part 3: Fix IR building of hash literals

* Hash literals were broken similarly as array literals.
* Updated the spec for #2574.

Author: subbuss

core/src/main/java/org/jruby/ir/IRBuilder.java

@@ -2393,10 +2393,10 @@ public Operand buildHash(HashNode hashNode) {
                 splatKeywordArgument = build(pair.getValue());
                 break;
             } else {
-               keyOperand = build(key);
+               keyOperand = copyAndReturnValue(build(key));
             }
 
-            args.add(new KeyValuePair<>(keyOperand, build(pair.getValue())));
+            args.add(new KeyValuePair<Operand, Operand>(keyOperand, copyAndReturnValue(build(pair.getValue()))));
         }
 
         if (splatKeywordArgument != null) { // splat kwargs merge with any explicit kwargs

spec/regression/GH-2574_dont_clobber_variable.rb

@@ -1,9 +1,17 @@
 # https://github.com/jruby/jruby/issues/2574
 describe 'Local variable assignments should not get clobbered' do
-  it 'returns the right value' do
+  it 'returns the right value for array literals' do
     a = 0
     b = [a,a=1]
     expect(b).to eq([0,1])
   end
+
+  it 'returns the right value for hash literals' do
+    a = 0
+    b = { a => a, (a = 1) => a } # => { 1 => 1 } (MRI: {0=>0, 1=>1})
+    c = { a => a, a => (a = 2) } # => { 2 => 2 } (MRI: {1=>2})
+    expect(b).to eq({0=>0, 1=>1})
+    expect(c).to eq({1=>2})
+  end
 end