Cc: Paolo Bonzini <pbonz...@redhat.com> Cc: Richard Henderson <r...@twiddle.net> Signed-off-by: Aurelien Jarno <aurel...@aurel32.net> --- tcg/README | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-)
diff --git a/tcg/README b/tcg/README index 61b3899..d8fd17a 100644 --- a/tcg/README +++ b/tcg/README @@ -470,8 +470,19 @@ Floating point operations are not supported in this version. A previous incarnation of the code generator had full support of them, but it is better to concentrate on integer operations first. -On a 64 bit target, no assumption is made in TCG about the storage of -the 32 bit values in 64 bit registers. +On a 64 bit target, the values are transfered between 32 and 64-bit +registers by the mean of the following ops: +- trunc_shr_i64_i32 +- ext_i32_i64 +- extu_i32_i64 + +These ops are all optional in that case they are implemented as mov. +This is to allow some optimizations if the target maintains registers +zero or sign extended. For example a MIPS64 CPU requires that all +32-bit values are stored sign-extended in the registers. This means +the trunc_shr_i64_i32 should sign-extend the value when moving it +from a 64-bit to a 32-bit register. It also means ext_i32_i64 can be +implemented as a simple mov as the value is already sign extended. 4.2) Constraints -- 2.1.4
