私はLLVMコードの最適化について読んでいます。多くの例でoptコマンドオプションを適用しようとしましたが効果がありません。 example.HereについてdeadCode.cppと呼ばれるC++コードです:私はこのような打ち鳴らすとLLVM IRを生成llvmコードの最適化オプションが機能しない
#include<stdio.h>
int square(int x){
return x*x;
}
int main(){
int a=2;
int b=3;
int c=4;
int result =square(a);
printf("%d\n",b);
}
:
打ち鳴らすの-emit-LLVM -S deadCode.cpp -o deadCodeBefore
を
と結果ファイルdeadCodeBefore内容は次のとおりです。
; ModuleID = 'deadCode.cpp'
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-pc-linux-gnu"
@.str = private unnamed_addr constant [4 x i8] c"%d\0A\00", align 1
; Function Attrs: nounwind uwtable
define i32 @_Z6squarei(i32 %x) #0 {
%1 = alloca i32, align 4
store i32 %x, i32* %1, align 4
%2 = load i32, i32* %1, align 4
%3 = load i32, i32* %1, align 4
%4 = mul nsw i32 %2, %3
ret i32 %4
}
; Function Attrs: norecurse uwtable
define i32 @main() #1 {
%a = alloca i32, align 4
%b = alloca i32, align 4
%c = alloca i32, align 4
%result = alloca i32, align 4
store i32 2, i32* %a, align 4
store i32 3, i32* %b, align 4
store i32 4, i32* %c, align 4
%1 = load i32, i32* %a, align 4
%2 = call i32 @_Z6squarei(i32 %1)
store i32 %2, i32* %result, align 4
%3 = load i32, i32* %b, align 4
%4 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str, i32 0, i32 0), i32 %3)
ret i32 0
}
declare i32 @printf(i8*, ...) #2
attributes #0 = { nounwind uwtable "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-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2" "unsafe-fp-math"="false" "use-soft-float"="false" }
attributes #1 = { norecurse uwtable "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-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2" "unsafe-fp-math"="false" "use-soft-float"="false" }
attributes #2 = { "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-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2" "unsafe-fp-math"="false" "use-soft-float"="false" }
!llvm.ident = !{!0}
!0 = !{!"clang version 3.8.0-2ubuntu4 (tags/RELEASE_380/final)"}
最適化のコmmand私が使用:
オプト-S -adce deadCodeBefore -o deadCodeAfter1
私は、彼らは何の効果もありませんので、それは二乗関数ともC変数の宣言への呼び出しを削除する必要が読んでいます。しかし結果は同じです。ここにdeadCodeBeforeと同じdeadCodeAfter1があります:
; ModuleID = 'deadCodeBefore'
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-pc-linux-gnu"
@.str = private unnamed_addr constant [4 x i8] c"%d\0A\00", align 1
; Function Attrs: nounwind uwtable
define i32 @_Z6squarei(i32 %x) #0 {
%1 = alloca i32, align 4
store i32 %x, i32* %1, align 4
%2 = load i32, i32* %1, align 4
%3 = load i32, i32* %1, align 4
%4 = mul nsw i32 %2, %3
ret i32 %4
}
; Function Attrs: norecurse uwtable
define i32 @main() #1 {
%a = alloca i32, align 4
%b = alloca i32, align 4
%c = alloca i32, align 4
%result = alloca i32, align 4
store i32 2, i32* %a, align 4
store i32 3, i32* %b, align 4
store i32 4, i32* %c, align 4
%1 = load i32, i32* %a, align 4
%2 = call i32 @_Z6squarei(i32 %1)
store i32 %2, i32* %result, align 4
%3 = load i32, i32* %b, align 4
%4 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([4 x i8], [4 x i8]* @.str, i32 0, i32 0), i32 %3)
ret i32 0
}
declare i32 @printf(i8*, ...) #2
attributes #0 = { nounwind uwtable "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-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2" "unsafe-fp-math"="false" "use-soft-float"="false" }
attributes #1 = { norecurse uwtable "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-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2" "unsafe-fp-math"="false" "use-soft-float"="false" }
attributes #2 = { "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-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2" "unsafe-fp-math"="false" "use-soft-float"="false" }
!llvm.ident = !{!0}
!0 = !{!"clang version 3.8.0-2ubuntu4 (tags/RELEASE_380/final)"}