How to save the variable name when use clang to generate llvm ir？

Question

I generate ir by use 'clang -S -emit-llvm test.c'.

int main(int argc, char **argv)
{
    int* a=0;
    a=(int *)malloc(sizeof(int));
    printf("hello world\n");
    return 0;
}

and this is the ir:

define i32 @main(i32, i8**) #0 {
  %3 = alloca i32, align 4
  %4 = alloca i32, align 4
  %5 = alloca i8**, align 8
  %6 = alloca i32*, align 8
  store i32 0, i32* %3, align 4
  store i32 %0, i32* %4, align 4
  store i8** %1, i8*** %5, align 8
  store i32* null, i32** %6, align 8
  %7 = call noalias i8* @malloc(i64 4) #3
  %8 = bitcast i8* %7 to i32*
  store i32* %8, i32** %6, align 8
  %9 = call i32 (i8*, ...) @printf(i8* getelementptr inbounds ([13 x i8], [13 x i8]* @.str, i32 0, i32 0))
  ret i32 0
}

how can I make the variable name remain unchanged，like a still %a ，not %3？

Answer 1

Actually dropping of variable names is a feature and needs to be activated with -discard-value-names. Clang in a release build does this by its own (a self compiled clang in debug mode not).

You can circumvent it with

clang <your-command-line> -###

Then copy the output and drop -discard-value-names.

Newer clang version (since 7) expose the flag to the normal command line:

clang -fno-discard-value-names <your-command-line>

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