llvm dev - Dec 2016 - How to actively reclaim stack memory

For help:

for loop lead to stack overflow, want to actively reclaim stack memory of alloc
instruction.

How to actively reclaim stack memory ?





haifeng.qin at wellintech.com
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On 15 Dec 2016, at 07:26, haifeng.qin at wellintech.com via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> 
> For help:
> 
> for loop lead to stack overflow, want to actively reclaim stack memory of
alloc instruction.
> 
> How to actively reclaim stack memory ?
This sounds as if you’re putting the alloca inside the loop, not in the entry
basic block and reusing it.  If you need the same amount of storage for each
loop iteration, then you should put the alloca in the entry basic block and use
the lifetime start / stop intrinsics in the loop to mark reuse of the memory. 
If you need different sized allocations, then you will need to use the stack
save and stack restore intrinsics inside the loop to reset the stack allocations
in the loop.

David

Thanks very much for your help!

Qin



haifeng.qin at wellintech.com
 
From: David Chisnall
Date: 2016-12-15 18:01
To: haifeng.qin at wellintech.com
CC: llvm-dev
Subject: Re: [llvm-dev] How to actively reclaim stack memory
On 15 Dec 2016, at 07:26, haifeng.qin at wellintech.com via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> 
> For help:
> 
> for loop lead to stack overflow, want to actively reclaim stack memory of
alloc instruction.
> 
> How to actively reclaim stack memory ?
 
This sounds as if you’re putting the alloca inside the loop, not in the entry
basic block and reusing it.  If you need the same amount of storage for each
loop iteration, then you should put the alloca in the entry basic block and use
the lifetime start / stop intrinsics in the loop to mark reuse of the memory. 
If you need different sized allocations, then you will need to use the stack
save and stack restore intrinsics inside the loop to reset the stack allocations
in the loop.
 
David
 
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