diff mbox

Remove x86_64 math_private.h asms

Message ID alpine.DEB.2.21.1809051710310.25040@digraph.polyomino.org.uk
State Committed
Commit 4e7fbdd7c2884e8909ea8f2f59d52f7d0c699252
Headers show

Commit Message

Joseph Myers Sept. 5, 2018, 5:11 p.m. UTC
The x86_64 math_private.h has asm versions of the macros to
reinterpret between floating-point and integer types.

This is the sort of thing we now strongly discourage; the expectation
in such cases, where the generic C code gives the compiler all the
information needed about the required semantics, is that you should
get the compiler to do the right thing for the generic C code rather
than writing an asm version.

Trivial tests showed GCC generates the expected single instructions
for reinterpretation from floating point to integer.  In the other
direction, it goes via memory when the asms don't; I asked about this
in GCC bug 87236 and was advised this was deliberate for generic
tuning because it was faster that way on some AMD processors (but
-mtune=intel, and -Os with the latest GCC, avoid going via memory).
The asms don't and can't know about those tuning details, so that's
evidence that they are actually making the code worse.

This patch removes the asms accordingly.  Tested for x86_64.  Does
anyone see a reason not to make this change?

2018-09-05  Joseph Myers  <joseph@codesourcery.com>

	* sysdeps/x86_64/fpu/math_private.h (MOVD): Remove macro.
	(MOVQ): Likewise.
	(EXTRACT_WORDS64): Likewise.
	(INSERT_WORDS64): Likewise.
	(GET_FLOAT_WORD): Likewise.
	(SET_FLOAT_WORD): Likewise.

Comments

Joseph Myers Sept. 11, 2018, 2:52 p.m. UTC | #1
Now committed.
diff mbox

Patch

diff --git a/sysdeps/x86_64/fpu/math_private.h b/sysdeps/x86_64/fpu/math_private.h
index fcc8537d40..306875f92b 100644
--- a/sysdeps/x86_64/fpu/math_private.h
+++ b/sysdeps/x86_64/fpu/math_private.h
@@ -1,50 +1,6 @@ 
 #ifndef X86_64_MATH_PRIVATE_H
 #define X86_64_MATH_PRIVATE_H 1
 
-/* We can do a few things better on x86-64.  */
-
-#if defined __AVX__ || defined SSE2AVX
-# define MOVD "vmovd"
-# define MOVQ "vmovq"
-#else
-# define MOVD "movd"
-# define MOVQ "movq"
-#endif
-
-/* Direct movement of float into integer register.  */
-#define EXTRACT_WORDS64(i, d)						      \
-  do {									      \
-    int64_t i_;								      \
-    asm (MOVQ " %1, %0" : "=rm" (i_) : "x" ((double) (d)));		      \
-    (i) = i_;								      \
-  } while (0)
-
-/* And the reverse.  */
-#define INSERT_WORDS64(d, i) \
-  do {									      \
-    int64_t i_ = i;							      \
-    double d__;								      \
-    asm (MOVQ " %1, %0" : "=x" (d__) : "rm" (i_));			      \
-    d = d__;								      \
-  } while (0)
-
-/* Direct movement of float into integer register.  */
-#define GET_FLOAT_WORD(i, d) \
-  do {									      \
-    int i_;								      \
-    asm (MOVD " %1, %0" : "=rm" (i_) : "x" ((float) (d)));		      \
-    (i) = i_;								      \
-  } while (0)
-
-/* And the reverse.  */
-#define SET_FLOAT_WORD(f, i) \
-  do {									      \
-    int i_ = i;								      \
-    float f__;								      \
-    asm (MOVD " %1, %0" : "=x" (f__) : "rm" (i_));			      \
-    f = f__;								      \
-  } while (0)
-
 #include_next <math_private.h>
 
 #ifdef __SSE4_1__