New fix for duplicate methods in the AltJit jit-diff output (dotnet#3…

…9751)

src/coreclr/src/zap/zapinfo.cpp

@@ -496,36 +496,50 @@ void ZapInfo::CompileMethod()
  m_pImage->m_stats->m_ilCodeSize += m_currentMethodInfo.ILCodeSize;
  }
 
- CorJitResult res = CORJIT_SKIPPED;
+ CorJitResult res = CORJIT_SKIPPED; // FAILED() returns true for this value
 
  BYTE *pCode;
  ULONG cCode;
+ bool doNormalCompile = true;
 
 #ifdef ALLOW_SXS_JIT_NGEN
+
+ // Only retry the JIT compilation when we have a different JIT to run
+ // Often we see both COMPlus_AltJIT and COMPlus_AltJitNgen set
+ // which results in both JIT compilers set to the same altjit
+ //
+ doNormalCompile = (m_zapper->m_alternateJit != m_zapper->m_pJitCompiler);
+
+ // Compile this method using the AltJitNgen compiler
+ //
  if (m_zapper->m_alternateJit)
  {
  res = m_zapper->m_alternateJit->compileMethod( this,
  &m_currentMethodInfo,
  CORJIT_FLAGS::CORJIT_FLAG_CALL_GETJITFLAGS,
  &pCode,
  &cCode);
- if (FAILED(res))
+
+ // The above compileMethod call will typically return CORJIT_SKIPPED
+ if (doNormalCompile && FAILED(res))
  {
  // We will fall back to the "main" JIT on failure.
  ResetForJitRetry();
  }
  }
+
 #endif // ALLOW_SXS_JIT_NGEN
 
- if (FAILED(res))
+ // Compile this method using the normal JIT compiler
+ //
+ if (doNormalCompile && FAILED(res))
  {
  ICorJitCompiler * pCompiler = m_zapper->m_pJitCompiler;
  res = pCompiler->compileMethod(this,
- &m_currentMethodInfo,
- CORJIT_FLAGS::CORJIT_FLAG_CALL_GETJITFLAGS,
- &pCode,
- &cCode);
-
+ &m_currentMethodInfo,
+ CORJIT_FLAGS::CORJIT_FLAG_CALL_GETJITFLAGS,
+ &pCode,
+ &cCode);
  if (FAILED(res))
  {
  ThrowExceptionForJitResult(res);