http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60101
Bug ID: 60101
Summary: Long compile times when mixed complex floating point
datatypes are used in lengthy expressions
Product: gcc
Version: 4.8.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: thorstenkurth at me dot com
Created attachment 32071
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=32071&action=edit
Archive which includes test case.
In the example I copied below, the double.c file compiles instantly whereas the
float.c file takes very long. This is a truncated version of an even longer
file (more lines of code in the loop) and the compile time for the float.c file
grows like N^3, where N is the number of lines. Here is the output of the long
version for 4.8.2:
0x40ae17 do_spec_1
../../gcc-4.8.2-src/gcc-4.8.2/gcc/gcc.c:5269
0x40ae17 do_spec_1
../../gcc-4.8.2-src/gcc-4.8.2/gcc/gcc.c:5269
0x40c875 process_brace_body
../../gcc-4.8.2-src/gcc-4.8.2/gcc/gcc.c:5872
0x40c875 process_brace_body
../../gcc-4.8.2-src/gcc-4.8.2/gcc/gcc.c:5872
0x40c875 handle_braces
../../gcc-4.8.2-src/gcc-4.8.2/gcc/gcc.c:5786
0x40c875 handle_braces
../../gcc-4.8.2-src/gcc-4.8.2/gcc/gcc.c:5786
0x40ae17 do_spec_1
../../gcc-4.8.2-src/gcc-4.8.2/gcc/gcc.c:5269
0x40c875 process_brace_body
../../gcc-4.8.2-src/gcc-4.8.2/gcc/gcc.c:5872
and more messages like that
The attached files both compile, but they the float.c takes significantly
longer.
The only difference between those files is that the temporary variable sum is
double complex in the working version and float complex in the non-working
version. So I guess, the compiler tries to reorganize the complex
multiplications and additions so that intermediate floating point results can
be used (this is what I guess). Both files compile using the icc (>=11.0) and
clang/LLVM almost instantly. It also works for gcc<=4.4.
