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Re: Fix/work around PR57676, LRA terminates prematurely


On 02/22/2016 07:34 AM, Richard Biener wrote:

Hum, but then you get to "inifinite" compiles again when LRA is buggy
or the user presents it with an impossible to handle asm.
Neither should be happening in practice, even an impossible asm should cause LRA to halt in some way or another.

In practice looping has occurred due to bugs in machine descriptions are are typically seen during development/porting. Hence the desire to put it under -fchecking for gcc-6 and possibly implement something smarter for gcc-7 (where we'd track more precisely whether or not we're making forward progress).


I don't think that's a good idea - maybe bumping the limit is the way to
go instead?
No, because one just needs to build a longer chain of insns needing reloading.


30 constraint passes sounds excessive and a sign of a bug to me anyway.
Not really. If you look at the testcase and the chain of reloads, it's legitimate. Essentially each pass exposes a case where spill a register in an insn that previously had a register allocated.

Jeff


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