[llvm-dev] tool options to generate spill code (original) (raw)

Priyanka Panigrahi via llvm-dev llvm-dev at lists.llvm.org
Wed Feb 12 02:35:56 PST 2020

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 -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20200212/f7bdcec1/attachment.html>

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