Some macro-assembler methods use lr as scratch. This doesn't work well with the baseline compiler's IC stubs since lr holds the return address. Simplest fix for now is to make it configurable, so that Ion can keep using lr and baseline can set it to one of the unused registers.

Comment on attachment 686055 [details] [diff] [review] Patch for inbound Review of attachment 686055 [details] [diff] [review]: ----------------------------------------------------------------- ::: js/src/ion/arm/MacroAssembler-arm.h @@ +31,5 @@ > + // defaults to lr, since it's non-allocatable (as it can be clobbered by some > + // instructions). Allow the baseline compiler to override this though, since > + // baseline IC stubs rely on lr holding the return address. > + Register secondScratchReg_; > + minor nit: would it be possible to make this a const, and only set it in the constructor? Having the scratch change mid-run shouldn't affect anything, but I don't see why that would be a particularly useful ability.

https://hg.mozilla.org/integration/mozilla-inbound/rev/bca4d501d3ff (Nit was discussed on IRC.)