fixup! Add atomics support to asmjs

llvm/lib/CheerpWriter/CheerpWriter.cpp

@@ -4876,20 +4876,6 @@ void CheerpWriter::compileAtomicCmpXchg(const AtomicCmpXchgInst& ai, PARENT_PRIO
 	if (shift == 0)
 		shiftPrio = LOWEST;
 
-	// Compare Exchange can be called even if there are no uses, because it has side effects. In
-	// this specific case, we do not (and cannot) assign the result to a value and do the comparison.
-	StringRef reg2;
-	if (!ai.use_empty())
-	{
-		// We need to use the compare operand twice, so we load it into the second register first.
-		reg2 = namegen.getName(&ai, 1);
-		stream << "((" << reg2 << "=";
-		// We end up using compileOperand on the cmpOp twice. But this is ok, since we make sure
-		// that a compare operand to an AtomicCmpXchg instruction is never inlineable.
-		compileOperand(cmpOp, BIT_OR);
-		stream << "|0),";
-	}
-	// Now we compile the main atomic compare exchange function.
 	stream << namegen.getBuiltinName(NameGenerator::Builtin::ATOMICCMPXCHG) << "(";
 	if (t->isIntegerTy(1) || t->isIntegerTy(8))
 		stream << "8,";
@@ -4905,24 +4891,21 @@ void CheerpWriter::compileAtomicCmpXchg(const AtomicCmpXchgInst& ai, PARENT_PRIO
 	if (shift != 0)
 		stream << ">>" << shift;
 	stream << ",";
-	// If this instruction has uses, the compare operand has been stored in the second register
-	// for this instruction. Otherwise, use the compare operand directly.
-	if (!ai.use_empty())
-		stream << reg2;
-	else
-		compileOperand(cmpOp, BIT_OR);
+	compileOperand(cmpOp, BIT_OR);
 	stream << "|0,";
 	compileOperand(newValOp, BIT_OR);
 	stream << "|0)|0";
-	if (!ai.use_empty())
-		stream << ")";
 
-	// Finally compile the second part of this instruction, the comparison between the loaded value
-	// and the compare operand (which is in the second register for this instruction).
+	// Compile the second part of this instruction, the comparison between the loaded value
+	// and the compare operand. A compare operand to a cmpxchg instruction cannot be inlined, so
+	// calling compileOperand twice is safe.
+	// We only compile this part if this instruction has uses.
 	if (!ai.use_empty())
 	{
 		stream << ";" << NewLine;
-		stream << reg2 << "=(" << namegen.getName(&ai, 0) << "|0)==(" << reg2 << "|0)";
+		stream << namegen.getName(&ai, 1) << "=(" << namegen.getName(&ai, 0) << "|0)==(";
+		compileOperand(cmpOp, BIT_OR);
+		stream << "|0)";
 	}
 }