[PATCH] D126392: [RISCV] Use two ADDIs to do some stack pointer adjustments.

[Craig Topper via Phabricator via llvm-commits]

craig.topper added inline comments.


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Comment at: llvm/lib/Target/RISCV/RISCVFrameLowering.cpp:309
 
-    Register ScratchReg = MRI.createVirtualRegister(&RISCV::GPRRegClass);
-    TII->movImm(MBB, MBBI, DL, ScratchReg, Val, Flag);
-    BuildMI(MBB, MBBI, DL, TII->get(Opc), DestReg)
+  // Try to split the offset across two ADDIs. We need make sure we keep the
+  // stack pointer aligned after each ADDI. We need to determine the maximum
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reames wrote:
> Is there anything here that guarantees stack alignment must be smaller than 12 bits?  If not, I don't think your statement about -2048 always being aligned holds.  
> 
> On the positive vs negative direction, shouldn't we always be able to use the same constant by simply swapping the ADD for a SUB?  
As far as I know the stack align is part of the RISCVFrameLowering constructor. It doesn’t change per function. Unless someone changes it from 16 to a huge value it should be true.

There is no SUBI instruction.




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  https://reviews.llvm.org/D126392/new/

https://reviews.llvm.org/D126392