https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66086
Bug ID: 66086
Summary: Casting a pointer to a double confuses the optimizer
Product: gcc
Version: 4.9.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: agriff at tin dot it
Target Milestone: ---
Created attachment 35510
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35510&action=edit
Small program showing the problem
When compiling
double doit() {
double *ptr = (double *)malloc(sizeof(double));
ptr[0] = 3.14;
return (double)((uintptr_t) ptr);
}
the generated code doesn't initialize the memory returned by `malloc` when the
optimization level is -O2.
This happens both in 64-bit mode and in 32-bit mode (where the size of
uintptr_t is 4 bytes and all theoretic values can be represented exactly in a
double); note that on x86-64 the used values are 48-bit only and a double
provides enough accuracy to store them correctly.
Attached is a full program showing the issue (compiled with -O0 the result is
correct, compiled with -O2 the result is wrong).
