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Help with reload bug, please


How does reload ensure that an SImode value (re)loaded into an FP register has a valid stack index?

The FP load instruction allows a smaller index range than the integer equivalent, but nothing checks the destination register, only the source mode.

I'm trying to solve a problem in which GCC 4.1 gets this wrong, but AFAICT this code works exactly the same now as then (although I don't have a testcase). IOW, unless I'm missing something, the only reason this doesn't fail all the time is that it's quite rare for the register pressure to cause just this value to spill in a function that has a stack frame >1KB and the index happens to be beyond the limit.

My target is ARMv7a with VFP. The code is trying to cast an int to a float. The machine description is such that the preferred route is to load the value first into a general register, transfer it to the VFP register, and then convert. It's only possible to get it to load directly to the VFP register if all the general registers are in use. This makes it very hard to write a synthetic testcase.

I can "fix" the problem by rewriting arm_legitimate_index_p such that it assumes all SImode access might be VFP loads, but that seems suboptimal.

Any suggestions would be appreciated!

Thanks

Andrew


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