Hello!
I would like to propose an ABI adjustment for the aloha OSF/1 ABI. To
quote explanation in the patch:
--q--
/* Pass float and _Complex float variable arguments by reference.
This avoids 64-bit store from a FP register to a pretend args save area
and subsequent 32-bit load from the saved location to a FP register.
Note that 32-bit loads and stores to/from a FP register on alpha reorder
bits to form a canonical 64-bit value in the FP register. This fact
invalidates compiler assumption that 32-bit FP value lives in the lower
32-bits of the passed 64-bit FP value, so loading the 32-bit value from
the stored 64-bit location using 32-bit FP load is invalid on alpha.
This introduces sort of ABI incompatibility, but until _Float32 was
introduced, C-family languages promoted 32-bit float variable arg to
a 64-bit double, and it was not allowed to pass float as a varible
argument. Passing _Complex float as a variable argument never
worked on alpha. Thus, we have no backward compatibility issues
to worry about, and passing un-promoted _Float32 and _Complex float
as a variable argument will actually work in the future. */
--/q--
Another rationale for the adjustment is, that "other" compilers do not
know about _Float32 and _Complex float, the official ABI pre-dates
some of these types by a decade or more (I was not able to find the
authoritative OSF/1 ABI document on the net...), and lastly ... gcc is
the last compiler that keeps this dead architecture alive, so IMO we
can consider it as a de-facto implementer of the ABI.
Following this ABI adjustment, we can also fix libffi, where
libffi.complex/cls_complex_va_float.c says:
--q--
/* Alpha splits _Complex into two arguments. It's illegal to pass
float through varargs, so _Complex float goes badly. In sort of
gets passed as _Complex double, but the compiler doesn't agree
with itself on this issue. */
/* { dg-do run { xfail alpha*-*-* } } */
--/q--
2016-09-02 Uros Bizjak <[email protected]>
* config/alpha/alpha.c (alpha_pass_by_reference): Pass un-named
SFmode and SCmode arguments by reference.
Patch was bootstrapped and regression tested on alphaev68-linux-gnu
for all default languages plus obj-c++ and go.
Any comments?
Uros.
diff --git a/gcc/config/alpha/alpha.c b/gcc/config/alpha/alpha.c
index 702cd27..81cef4e 100644
--- a/gcc/config/alpha/alpha.c
+++ b/gcc/config/alpha/alpha.c
@@ -5754,8 +5754,29 @@ static bool
alpha_pass_by_reference (cumulative_args_t ca ATTRIBUTE_UNUSED,
machine_mode mode,
const_tree type ATTRIBUTE_UNUSED,
- bool named ATTRIBUTE_UNUSED)
+ bool named)
{
+ /* Pass float and _Complex float variable arguments by reference.
+ This avoids 64-bit store from a FP register to a pretend args save area
+ and subsequent 32-bit load from the saved location to a FP register.
+
+ Note that 32-bit loads and stores to/from a FP register on alpha reorder
+ bits to form a canonical 64-bit value in the FP register. This fact
+ invalidates compiler assumption that 32-bit FP value lives in the lower
+ 32-bits of the passed 64-bit FP value, so loading the 32-bit value from
+ the stored 64-bit location using 32-bit FP load is invalid on alpha.
+
+ This introduces sort of ABI incompatibility, but until _Float32 was
+ introduced, C-family languages promoted 32-bit float variable arg to
+ a 64-bit double, and it was not allowed to pass float as a varible
+ argument. Passing _Complex float as a variable argument never
+ worked on alpha. Thus, we have no backward compatibility issues
+ to worry about, and passing unpromoted _Float32 and _Complex float
+ as a variable argument will actually work in the future. */
+
+ if (mode == SFmode || mode == SCmode)
+ return !named;
+
return mode == TFmode || mode == TCmode;
}
