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update comments on register clobbering

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git-svn-id: svn://localhost/ardour2/branches/3.0@6423 d708f5d6-7413-0410-9779-e7cbd77b26cf
This commit is contained in:
Paul Davis 2009-12-31 18:19:46 +00:00
parent 569226e64e
commit c6d5124269
1 changed files with 6 additions and 5 deletions
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11
libs/pbd/fpu.cc
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@ -21,11 +21,6 @@ FPU::FPU ()
return;
#endif
/* asm notes: although we explicitly save&restore ebx/rbx (stack pointer), we must tell
gcc that ebx,rbx is clobbered so that it doesn't try to use it as an intermediate
register when storing edx/rdx. gcc 4.3 didn't make this "mistake", but gcc 4.4
does, at least on x86_64.
*/
#ifndef USE_X86_64_ASM
asm volatile (
@ -41,6 +36,12 @@ FPU::FPU ()
#else
/* asm notes: although we explicitly save&restore rbx, we must tell
gcc that ebx,rbx is clobbered so that it doesn't try to use it as an intermediate
register when storing rbx. gcc 4.3 didn't make this "mistake", but gcc 4.4
does, at least on x86_64.
*/
asm volatile (
"pushq %%rbx\n"
"movq $1, %%rax\n"