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Diffstat (limited to 'gcc/doc/md.texi')
| -rw-r--r-- | gcc/doc/md.texi | 21 |
1 files changed, 21 insertions, 0 deletions
diff --git a/gcc/doc/md.texi b/gcc/doc/md.texi index bc1ec9d4f0..bbd91c2367 100644 --- a/gcc/doc/md.texi +++ b/gcc/doc/md.texi @@ -3027,6 +3027,27 @@ Altivec vector register @item wa Any VSX register if the -mvsx option was used or NO_REGS. +When using any of the register constraints (@code{wa}, @code{wd}, +@code{wf}, @code{wg}, @code{wh}, @code{wi}, @code{wj}, @code{wk}, +@code{wl}, @code{wm}, @code{ws}, @code{wt}, @code{wu}, @code{wv}, +@code{ww}, or @code{wy}) that take VSX registers, you must use +@code{%x<n>} in the template so that the correct register is used. +Otherwise the register number output in the assembly file will be +incorrect if an Altivec register is an operand of a VSX instruction +that expects VSX register numbering. + +@smallexample +asm ("xvadddp %x0,%x1,%x2" : "=wa" (v1) : "wa" (v2), "wa" (v3)); +@end smallexample + +is correct, but: + +@smallexample +asm ("xvadddp %0,%1,%2" : "=wa" (v1) : "wa" (v2), "wa" (v3)); +@end smallexample + +is not correct. + @item wd VSX vector register to hold vector double data or NO_REGS. |