Avoid __vla_alloc for a local array defined inside a function

Ashish Kapania

Hi Compiler Gurus,

I am declaring an array inside a function whose length is specified by a global constant. Looking at the dis-assembly, I noticed that the compiler is making a __vla_alloc call to allocate memory for the array. Since this function is on the critical path, I need to avoid any memory allocation calls inside it. Is there a way I can continue to use the global constant to specify the array length but avoid the alloc call ? I know I can use an integer literal to specify the array length but want to purposely avoid that as the array length is statically configurable at build time.

Best,

Ashish

Edit: I am using TI's ARM compiler and the target is Cortex-R5

over 9 years ago

0 George Mock over 9 years ago

TI__Guru**** 251230 points

I must not understand what you are doing. I cannot reproduce it. Please send in a test case. Your probably need to preprocess the source file. Also show the compiler version and all the build options exactly as the compiler sees them.

Thanks and regards,

-George

0 Archaeologist over 9 years ago in reply to George Mock

TI__Guru* 84285 points

George, try this (it's a C99 feature):

const int x = 5;
int func() { int arry[x]; call(&arry[0]); return arry[0]; }

0 Archaeologist over 9 years ago

TI__Guru* 84285 points

Unfortunately I don't think there's a way to get what you want while using a const variable. When this feature was implemented, we didn't consider that you'd want to make a variable length array with a constant size. I'll add an enhancement request to optimize this. As a workaround, define the global as a #define.