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This builds on some frame-lowering code that has existed since 2005 (r24224) but was disabled in 2008 (r48188) because it needed base pointer support to function correctly. This implementation follows the strategy suggested by Dale Johannesen in r48188 where the following comment was added: This does not currently work, because the delta between old and new stack pointers is added to offsets that reference incoming parameters after the prolog is generated, and the code that does that doesn't handle a variable delta. You don't want to do that anyway; a better approach is to reserve another register that retains to the incoming stack pointer, and reference parameters relative to that. And now we do exactly that. If we don't need a frame pointer, then we use r31 as a base pointer. If we do need a frame pointer, then we use r30 as a base pointer. The base pointer retains the value of the stack pointer before it was decremented in the prologue. We then use the base pointer to resolve all negative frame indicies. The basic scheme follows that for base pointers in the X86 backend. We use a base pointer when we need to dynamically realign the incoming stack pointer. This currently applies only to static objects (dynamic allocas with large alignments, and base-pointer support in SjLj lowering will come in future commits). git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186478 91177308-0d34-0410-b5e6-96231b3b80d8
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