MCompare already supports uint32 comparisons, though they are just used by asm.js. The attached patch allows this comparison to be used during normal Ion compilation as well, by looking for and removing uint32 coercions (x >>> 0) on the compare's operands. This eliminates many bailouts that are currently taken on the asm.js bullet demo. Just pattern matching the comparison's inputs should be good enough for asm.js applications, as int32 vs. uint32 operations are distinguished with these coercions on the operands (rather than at the variable level). There are other places where uint32 coercions appear --- div, mod, fp div (?) --- but the fix there is more involved and can be done separately.

Comment on attachment 748206 [details] [diff] [review] patch Review of attachment 748206 [details] [diff] [review]: ----------------------------------------------------------------- It would be nice to add MIRType_Uint32 and handle uint32 values better (bug 750947), but in the meantime this seems fine.