I am currently playing around with LLVM and am trying to write a few optimizers to familiarize myself with opt and clang. I wrote a test.c file that is as follow:
int foo(int aa, int bb, int cc){ int sum = aa + bb; return sum/cc; } I compiled the source code and generated 2 .ll files, one unoptimized and one with mem2reg optimizer pass:
clang -emit-llvm -O0 -c test.c -o test.bc llvm-dis test.bc opt -mem2reg -S test.ll -o test-mem2reg.ll Both .ll files gave me the following output:
ModuleID = 'test.bc' source_filename = "test.c" target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128" target triple = "x86_64-unknown-linux-gnu" ; Function Attrs: noinline nounwind optnone uwtable define i32 @foo(i32 %aa, i32 %bb, i32 %cc) #0 { entry: %aa.addr = alloca i32, align 4 %bb.addr = alloca i32, align 4 %cc.addr = alloca i32, align 4 %sum = alloca i32, align 4 store i32 %aa, i32* %aa.addr, align 4 store i32 %bb, i32* %bb.addr, align 4 store i32 %cc, i32* %cc.addr, align 4 %0 = load i32, i32* %aa.addr, align 4 %1 = load i32, i32* %bb.addr, align 4 %add = add nsw i32 %0, %1 store i32 %add, i32* %sum, align 4 %2 = load i32, i32* %sum, align 4 %3 = load i32, i32* %cc.addr, align 4 %div = sdiv i32 %2, %3 ret i32 %div } attributes #0 = { noinline nounwind optnone uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" } !llvm.module.flags = !{!0} !llvm.ident = !{!1} !0 = !{i32 1, !"wchar_size", i32 4} !1 = !{!"clang version 6.0.0 (trunk 314616)"} So it seems that my mem2reg pass didn't work! What would be the problem?