3 ms·

> LLVM doesn't have an intermediate representation comparable to Gimple: LLIR seems to be at the level of the registers rather than the nice abstract Gimple LL

> LLVM doesn't have an intermediate representation comparable to Gimple: LLIR seems to be at the level of the registers rather than the nice abstract Gimple LLVM variables are sometimes called registers but they are machine independent. The bit width is arbitrary (e.g., you can create a 129-bit integer). The use of the term register is a misleading analogy; often LLVM-IR is compared to assembly language so the use of the term register was also used. I do not know GIMPLE and couldn't find a good description of the IR instructions. But, it seems that LLVM IR is somewhat similar to low GIMPLE.

bedatadriven 12y ago
Will have to take another look, but it still sounds to me like LLVM IR is more comparable to RTL (https://gcc.gnu.org/onlinedocs/gccint/RTL.html#RTL https://gcc.gnu.org/onlinedocs/gccint/RTL.html#RTL). Gimple variables have types comparable with C types - you get pointers, arrays. For example: int sum10(int values[10]) { int i; int sum = 0; for(i=0;i<10;++i) { sum += values[i]; } values[0] = 342; return sum; } is compiled down to: sum10 (int * values) { long unsigned int D.1598; long unsigned int D.1599; int * D.1600; int D.1601; int D.1602; int i; int sum; sum = 0; i = 0; goto <D.1595>; <D.1594>: D.1598 = (long unsigned int) i; D.1599 = D.1598 * 4; D.1600 = values + D.1599; D.1601 = *D.1600; sum = D.1601 + sum; i = i + 1; <D.1595>: if (i <= 9) goto <D.1594>; else goto <D.1596>; <D.1596>: *values = 342; D.1602 = sum; return D.1602; }
- rwallace 12y ago
  As far as I know, LLVM does exactly the same thing; the LLVM representation of that code would have a different syntax of course, but semantically would be exactly equivalent to the Gimple version you've presented.

bedatadriven 12y ago

Will have to take another look, but it still sounds to me like LLVM IR is more comparable to RTL (https://gcc.gnu.org/onlinedocs/gccint/RTL.html#RTL https://gcc.gnu.org/onlinedocs/gccint/RTL.html#RTL). Gimple variables have types comparable with C types - you get pointers, arrays. For example: int sum10(int values[10]) { int i; int sum = 0; for(i=0;i<10;++i) { sum += values[i]; } values[0] = 342; return sum; } is compiled down to: sum10 (int * values) { long unsigned int D.1598; long unsigned int D.1599; int * D.1600; int D.1601; int D.1602; int i; int sum; sum = 0; i = 0; goto <D.1595>; <D.1594>: D.1598 = (long unsigned int) i; D.1599 = D.1598 * 4; D.1600 = values + D.1599; D.1601 = *D.1600; sum = D.1601 + sum; i = i + 1; <D.1595>: if (i <= 9) goto <D.1594>; else goto <D.1596>; <D.1596>: *values = 342; D.1602 = sum; return D.1602; }

rwallace 12y ago
As far as I know, LLVM does exactly the same thing; the LLVM representation of that code would have a different syntax of course, but semantically would be exactly equivalent to the Gimple version you've presented.