Testcase:
void f(float);
void g(double x) { f(-x); }
Using -fdump-tree-original shows that GCC understands the above code as
"f(-(float)x)", although it should really be "f((float)(-x))". As a
consequence, the generated code is not efficient (on x86), as GCC will have to
store x to memory as a float before loading it again and changing its sign.
Moreover, the computed value is not the expected one when the rounding mode is
a directed rounding, as the conversion happens before the sign change.
Tested with Debian GCC 3.3.6, 3.4.6, 4.0.4, and 4.1.2. Version 3.3 generates
the correct code, the other ones don't.
--
Summary: Incorrect interpretation of floating-point unary minus
Product: gcc
Version: 4.1.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: guillaume dot melquiond at ens-lyon dot fr
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29538
