[llvm-dev] tool options to generate spill code

[Priyanka Panigrahi via llvm-dev]

Hello,

For the following test case, reg.c

#include <stdio.h>

int getinput()
{
static int u=10;
return u++;
}

int main()
{

int a,b,c,d,e,f,g;

        a=getinput();
        b=getinput();
        c=getinput();
        d=getinput();
        e=getinput();
        f=getinput();
        g=getinput();

printf("%d %d %d %d %d %d %d\n",a,b,c,d,e,f,g);
a=b=c=d=e=f=g=0;
return 0;
}

*1. $clang reg.c -Xclang -disable-O0-optnone -S -emit-llvm -o reg.ll && opt
-mem2reg -S reg.ll -o reg.ll && llc --regalloc=greedy reg.ll -o reg.s*

*2. $clang reg.c -Xclang -disable-llvm-passes -S -emit-llvm -o reg.ll &&
opt -mem2reg -S reg.ll -o reg.ll && llc --regalloc=greedy reg.ll -o reg.s*

*3. $clang reg.c -S -emit-llvm -o reg.ll && opt -mem2reg -S reg.ll -o
reg.ll && llc --regalloc=greedy reg.ll -o reg.s*

Only 1. gives the spill code but it deletes the dead stores., 2 and 3 give
only allocas. Why so??

How -mem2reg works and what it depends on?

How to generate the spill code with dead stores?

Thank you.

Regards,
Priyanka
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