For the range of Radeon HD 4000/5000/6000 graphics cards tested, the R600 LLVM GPU back-end had no real change on the overall frame-rate for this id Software game. As mentioned already, there are other factors to measure the shader compiler/back-end performance, but as far as end-users are concerned of the open-source Radeon Linux graphics driver, there was no ultimate change in the gaming performance.
When running the Nexuiz open-source game, the results were close to the same between the stock R600g and LLVM back-ends although for the Radeon HD 5830 and HD 6770 graphics cards it appeared that the R600 LLVM GPU back-end might have resulted in slightly slower performance.
When running the open-source Reaction Quake 3 game, there wasn't any major change in performance except for the low-end Radeon HD 4550. The Radeon HD 4550 seemed to perform noticeably better with the LLVM back-end. The other Radeon HD 4870, HD 5830, and HD 6770 graphics cards only inched slightly higher when using the LLVM compiler back-end.