Simon Dardis 878c0b1b76 [mips] Optimize stack pointer adjustments. ...

Instead of always using addu to adjust the stack pointer when the
size out is of the range of an addiu instruction, use subu so that
a smaller constant can be generated.

This can give savings of ~3 instructions whenever a function has a
a stack frame whose size is out of range of an addiu instruction.

This change may break some naive stack unwinders.

Partially resolves PR/26291.

Thanks to David Chisnall for reporting the issue.

Reviewers: dsanders, vkalintiris

Differential Review: http://reviews.llvm.org/D21321

llvm-svn: 272666

2016-06-14 13:39:43 +00:00

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