With a tcc modified to compile GCC, running cc1 (the GCC C compiler) on itself required 518 seconds when compiled using GCC 3.4.2, 558 seconds using GCC 2.95.3, 545 using Microsoft C compiler, and 1145 seconds using tcc.To calculate the 49th Fibonacci number, it took a MS Visual C++ program approximately 18% longer than the TCC compiled program. A recursive Fibonacci algorithm on a 1.8 GHz Intel Centrino laptop with 512 MB RAM yields a noticeable difference in results between Microsoft Visual C++ compiler and TCC.It also does some simple register allocation, which prevents many extraneous save/load pairs inside a single statement. TCC performs a few optimizations, such as constant propagation for all operations, multiplications and divisions are optimized to shifts when appropriate, and comparison operators are specially optimized (by maintaining a special cache for the processor flags). TCC uses only some of the available registers (e.g., on x86 it never uses ebx, esi, or edi because they need to be preserved across function calls). TCC compiles every statement on its own, and at the end of each statement register values are written back to the stack and must be re-read even if the next line uses the values in registers (creating extraneous save/load pairs between statements).

TCC generates code in a single pass, and does not perform most of the optimizations performed by other compilers. In general, TCC's implementation emphasizes smallness instead of optimally-performing results.

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