[RFC PATCH] MIPS: math-emu: do not use bools for arithmetic

[RFC PATCH] MIPS: math-emu: do not use bools for arithmetic

[Manuel Lauss]

GCC-7 complains about a boolean value being used with an arithmetic
AND:

arch/mips/math-emu/cp1emu.c: In function 'cop1Emulate':
arch/mips/math-emu/cp1emu.c:838:14: warning: '~' on a boolean expression [-Wbool-operation]
  fpr = (x) & ~(cop1_64bit(xcp) == 0);    \
              ^
arch/mips/math-emu/cp1emu.c:1068:3: note: in expansion of macro 'DITOREG'
   DITOREG(dval, MIPSInst_RT(ir));
   ^~~~~~~
arch/mips/math-emu/cp1emu.c:838:14: note: did you mean to use logical not?
  fpr = (x) & ~(cop1_64bit(xcp) == 0);    \

Fix this by testing the bool and returning an int.
This also shrinks the size of the file object file by 312 bytes:

   text    data     bss     dec     hex filename
  11432       0       0   11432    2ca8 cp1emu.o-alt
  11120       0       0   11120    2b70 cp1emu.o

Signed-off-by: Manuel Lauss <manuel.lauss@gmail.com>
---
I'm unsure whether the patch is really correct, due to the unexpected
binary size reduction.  I do not have a hardfloat mips32 userland at hand
therefore I'd appreciate it if someone could test it!
Thanks!

 arch/mips/math-emu/cp1emu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/mips/math-emu/cp1emu.c b/arch/mips/math-emu/cp1emu.c
index f08a7b4facb9..f3a9bf5285e0 100644
--- a/arch/mips/math-emu/cp1emu.c
+++ b/arch/mips/math-emu/cp1emu.c
@@ -830,12 +830,12 @@ do {									\
 } while (0)
 
 #define DIFROMREG(di, x)						\
-	((di) = get_fpr64(&ctx->fpr[(x) & ~(cop1_64bit(xcp) == 0)], 0))
+	((di) = get_fpr64(&ctx->fpr[(x) & ~(cop1_64bit(xcp) == 0 ? 1 : 0)], 0))
 
 #define DITOREG(di, x)							\
 do {									\
 	unsigned fpr, i;						\
-	fpr = (x) & ~(cop1_64bit(xcp) == 0);				\
+	fpr = (x) & ~(cop1_64bit(xcp) == 0 ? 1 : 0);			\
 	set_fpr64(&ctx->fpr[fpr], 0, di);				\
 	for (i = 1; i < ARRAY_SIZE(ctx->fpr[x].val64); i++)		\
 		set_fpr64(&ctx->fpr[fpr], i, 0);			\
-- 
2.13.1

Re: [RFC PATCH] MIPS: math-emu: do not use bools for arithmetic

[Maciej W. Rozycki]

On Mon, 31 Jul 2017, Manuel Lauss wrote:

> I'm unsure whether the patch is really correct, due to the unexpected
> binary size reduction.  I do not have a hardfloat mips32 userland at hand
> therefore I'd appreciate it if someone could test it!

 What exactly are you unsure about?  Double operations using odd register 
indices in the 32-bit FPR mode are architecturally unpredictable.  Is this 
what concerns you?

> diff --git a/arch/mips/math-emu/cp1emu.c b/arch/mips/math-emu/cp1emu.c
> index f08a7b4facb9..f3a9bf5285e0 100644
> --- a/arch/mips/math-emu/cp1emu.c
> +++ b/arch/mips/math-emu/cp1emu.c
> @@ -830,12 +830,12 @@ do {									\
>  } while (0)
>  
>  #define DIFROMREG(di, x)						\
> -	((di) = get_fpr64(&ctx->fpr[(x) & ~(cop1_64bit(xcp) == 0)], 0))
> +	((di) = get_fpr64(&ctx->fpr[(x) & ~(cop1_64bit(xcp) == 0 ? 1 : 0)], 0))

 Umm, I find the expression somewhat hard to follow.  How about:

	((di) = get_fpr64(&ctx->fpr[(x) & ~(cop1_64bit(xcp) ^ 1))

?

>  #define DITOREG(di, x)							\
>  do {									\
>  	unsigned fpr, i;						\
> -	fpr = (x) & ~(cop1_64bit(xcp) == 0);				\
> +	fpr = (x) & ~(cop1_64bit(xcp) == 0 ? 1 : 0);			\

 Likewise:

	fpr = (x) & ~(cop1_64bit(xcp) ^ 1);				\

?

  Maciej

Re: [RFC PATCH] MIPS: math-emu: do not use bools for arithmetic

[Manuel Lauss]

On Wed, Aug 9, 2017 at 10:14 AM, Maciej W. Rozycki <macro@imgtec.com> wrote:
> On Mon, 31 Jul 2017, Manuel Lauss wrote:
>
>> I'm unsure whether the patch is really correct, due to the unexpected
>> binary size reduction.  I do not have a hardfloat mips32 userland at hand
>> therefore I'd appreciate it if someone could test it!
>
>  What exactly are you unsure about?  Double operations using odd register
> indices in the 32-bit FPR mode are architecturally unpredictable.  Is this
> what concerns you?

I was not able to find a definition for get_fpr by grepping the tree
for it, so I wasn't
sure whether only the LSB or all mattered.

Manuel

Re: [RFC PATCH] MIPS: math-emu: do not use bools for arithmetic

[Maciej W. Rozycki]

On Wed, 9 Aug 2017, Manuel Lauss wrote:

> >  What exactly are you unsure about?  Double operations using odd register
> > indices in the 32-bit FPR mode are architecturally unpredictable.  Is this
> > what concerns you?
> 
> I was not able to find a definition for get_fpr by grepping the tree
> for it, so I wasn't
> sure whether only the LSB or all mattered.

 It's in arch/mips/include/asm/processor.h; see BUILD_FPR_ACCESS.

  Maciej