[LLVMdev] Loop transformations using LLVM

[Rotem, Nadav]

Malveeka, 

You can use the LoopInfo analysis to find the induction variable. 

http://llvm.org/docs/doxygen/html/classllvm_1_1Loop.html#a72bbf45d2e00971f56bf8cfe4e1df01c

Cheers,
Nadav


From: llvmdev-bounces at cs.uiuc.edu [mailto:llvmdev-bounces at cs.uiuc.edu] On Behalf Of Malveeka Tewari
Sent: Thursday, May 05, 2011 14:51
To: llvmdev at cs.uiuc.edu
Subject: [LLVMdev] Loop transformations using LLVM

Hi 

I am trying to write up a transformation for the following code where instead of incrementing the loop variable by 1, I increment it by 2 ie.

for (i=0; i < THRES; i++) {
  //do something 
} 

gets transformed to 

for (i=0; i < THRES; i+=2) {
  //do something 
} 

I am thinking of transforming the llvm  bit-code in the following way.
Iterate over the function for the original code till I get the basicBlock for the for loop, then iterate over the instructions till I get the increment instruction and then add the same increment instruction so that the increment happens twice. 

I am still getting familiar with the llvm infrastructure and I am not sure if the above approach is even going to work. It'll be great if someone can suggest a better or more concrete way of doing the above transformation ? Is there already something similar in the source tree  that can I look up for ideas ?

Thanks!
Malveeka
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