http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47755
Summary: VSX code generates a TOC reference to clear memory
Product: gcc
Version: 4.6.0
Status: UNCONFIRMED
Severity: major
Priority: P3
Component: target
AssignedTo: meiss...@gcc.gnu.org
ReportedBy: meiss...@gcc.gnu.org
Host: powerpc64-linux
Target: powerpc64-linux
Build: powerpc64-linux
If you have an array of pointers or longs in 64-bit mode that you want to
clear, via loops like when you have automatic vectorization on:
for (i = 0; i < sizeof (array) / sizeof (array[0]); i++)
array[i] = 0;
The compiler generates the 128-bit zero constant, puts it into the constant
pool, and loads it from memory in order to set the array with vector
instructions.
Normally this would be a missed optimization, but we discovered it in compiling
_dl_start with -O3 -mcpu=power7, and at the time _dl_start is run, the TOC
registers are not yet set up, so the program crashes before it starts.
The cause of the bug is that V2DI mode is not true for either VSX_VECTOR_MODE
or ALTIVEC_VECTOR_MODE, since there are no native 64-bit operations in the VSX
or Altivec vector instructions. This means that easy_vector_constant fails,
which in turn makes LEGITIMATE_CONSTANT_P fail.
The solution is use macros that test whether Altivec/VSX memory references can
be done, instead of macros that say we have native arithmetic support for those
modes.
