Instcombine increases the number of instructions?

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1

Hello,
Can the Instcombine pass increase the number of instructions of a block?

2

Hi Rafael,

Can the Instcombine pass increase the number of instructions of a block?

while it usually doesn't, in theory it can increase the number of LLVM IR
instructions. I don't recall an example off the top of my head, but the
usual situation is that replacing some instruction I with a pair J, K
results in better code generation. There are a small number of cases like
this.

Ciao, Duncan.

3

I perform the Instcombine pass over Rijndael benchmark from Mibench ( suite of benchmarks). For compile, I use “-Instcount” for counting the instructions. Comparing the bench without transformation with the bench transformed by instcombine, I perceived a 10% of increase in the number of instructions. This is possible?

4

Hi Rafael,

I perform the Instcombine pass over Rijndael benchmark from Mibench ( suite of
benchmarks). For compile, I use "-Instcount" for counting the instructions.
Comparing the bench without transformation with the bench transformed by
instcombine, I perceived a 10% of increase in the number of instructions. This
is possible?

apparently so, otherwise you wouldn't be seeing it :slight_smile: Why don't you stick the
bitcode somewhere and provide instructions for reproducing this, otherwise it
is hard for us to make pertinent comments.

Ciao, Duncan.