Added a workaround for a very rare situation in which the compiler ig…

…nores SetFLAGSorEFLAGS in IRET. I am 93% sure it is a bug of clang on Linux. But, there always is a possibility that I am overlooking something.

src/cpu/CMakeLists.txt

@@ -21,6 +21,7 @@ i486fidelity.h
 i486runinstruction.h
 i486templatefunctions.h
 i486debugVxD.cpp
+i486garbage.cpp
 )
 target_link_libraries(cpu device ramrom inout cpputil)
 target_include_directories(cpu PUBLIC .)

src/cpu/i486.h

@@ -66,6 +66,8 @@ Therefore, the CPU class now is divided into three parts.  The base class, i486C
 
 class i486DXCommon : public CPU
 {
+public:
+	void ConsumeVariable(uint32_t); // See comments.
 public:
 	enum
 	{

src/cpu/i486garbage.cpp

@@ -0,0 +1,4 @@
+#include "i486.h"
+void i486DXCommon::ConsumeVariable(unsigned int variable)
+{
+}

src/cpu/i486runinstruction.h

@@ -7407,6 +7407,18 @@ unsigned int i486DXFidelityLayer<FIDELITY>::RunOneInstruction(Memory &mem,InOut
 				SetFLAGSorEFLAGS(inst.operandSize,eflags);
 				FIDELITY::RestoreIOPLBits(*this,ioplBits);
 				FIDELITY::RestoreIF(*this,ioplBits);
+
+				// If I print state.EFLAGS here, it is updated correctly.
+				// If I do not print state.EFLAGS, it is not updated from time to time.
+				// Looks like I stepped on a bug of clang.  I need to be careful to declare it as a clang bug,
+				// but it happens only in Linux using clang 6.0.0-1ubuntu2.
+				// It does not seem to happen with my clang on macOS.
+				// I need to let state.EFLAGS consumed by outside of this function, outside of this object file,
+				// to make it run correctly.  Otherwise, the compiler seems to ignore above SetFLAGSorEFLAGS.
+			#ifdef __linux__
+				ConsumeVariable(state.EFLAGS);
+			#endif
+
 				state.EFLAGS&=EFLAGS_MASK;
 				state.EFLAGS|=EFLAGS_ALWAYS_ON;
 
@@ -7446,6 +7458,9 @@ unsigned int i486DXFidelityLayer<FIDELITY>::RunOneInstruction(Memory &mem,InOut
 				typename FIDELITY::EFLAGS ioplBits;
 				FIDELITY::SaveEFLAGS(ioplBits,*this);
 				SetFLAGSorEFLAGS(inst.operandSize,eflags);
+			#ifdef __linux__
+				ConsumeVariable(state.EFLAGS);
+			#endif
 				FIDELITY::RestoreIOPLBits(*this,ioplBits);
 				FIDELITY::RestoreIF(*this,ioplBits);