x87 fldcw instruction triggers pending x87 exception. So if there is a
pending x87 exception and __mingw_setfp() is trying to disable some other
x87 type then it will trigger pending exception.
There is no non-waiting variant of x87 fldcw instruction. So for setting
new control word use x87 fldenv instruction like for setting new status
word. For using x87 fldenv instruction it is first need to load whole
x87 env via x87 fnstenv instruction.
Optimize code to not use x87 fnstenv when it is known that x87 fldenv would
not be used - when cw_mask or sw_mask is empty (used just for quering cw/sw).
---
mingw-w64-crt/misc/mingw_setfp.c | 63 +++++++++++++++++++-------------
1 file changed, 38 insertions(+), 25 deletions(-)
diff --git a/mingw-w64-crt/misc/mingw_setfp.c b/mingw-w64-crt/misc/mingw_setfp.c
index fb03781292ce..2298515128b5 100644
--- a/mingw-w64-crt/misc/mingw_setfp.c
+++ b/mingw-w64-crt/misc/mingw_setfp.c
@@ -121,13 +121,46 @@ void __mingw_setfp( unsigned int *cw, unsigned int
cw_mask,
unsigned long oldcw = 0, newcw = 0;
unsigned long oldsw = 0, newsw = 0;
unsigned int flags;
+ struct {
+ WORD control_word;
+ WORD unused1;
+ WORD status_word;
+ WORD unused2;
+ WORD tag_word;
+ WORD unused3;
+ DWORD instruction_pointer;
+ WORD code_segment;
+ WORD unused4;
+ DWORD operand_addr;
+ WORD data_segment;
+ WORD unused5;
+ } fenv;
cw_mask &= _MCW_EM | _MCW_IC | _MCW_RC | _MCW_PC;
sw_mask &= _MCW_EM;
+ if ((!sw || sw_mask == 0) && (!cw || cw_mask == 0))
+ {
+ /* Fast path: when we are not going to change sw/cw which is indicated
+ * by zero mask then load sw/cw via fast fnstsw/fnstcw instruction.
+ */
+ if (sw && sw_mask == 0)
+ __asm__ __volatile__( "fnstsw %0" : "=m" (newsw) );
+ if (cw && cw_mask == 0)
+ __asm__ __volatile__( "fnstcw %0" : "=m" (newcw) );
+ }
+ else
+ {
+ /* Slow path: when we are going to change sw/cw or we do not know yet
then
+ * load whole x87 env via slow fnstenv as it is needed for changing
sw/cw.
+ */
+ __asm__ __volatile__( "fnstenv %0" : "=m" (fenv) );
+ newsw = fenv.status_word;
+ newcw = fenv.control_word;
+ }
+
if (sw)
{
- __asm__ __volatile__( "fnstsw %0" : "=m" (newsw) );
oldsw = newsw;
flags = 0;
@@ -151,7 +184,6 @@ void __mingw_setfp( unsigned int *cw, unsigned int cw_mask,
if (cw)
{
- __asm__ __volatile__( "fnstcw %0" : "=m" (newcw) );
oldcw = newcw;
flags = 0;
@@ -198,35 +230,16 @@ void __mingw_setfp( unsigned int *cw, unsigned int
cw_mask,
if (*cw & _IC_AFFINE) newcw |= 0x1000;
}
- if (oldsw != newsw && (newsw & 0x3f))
+ /* For changing sw/cw always use fldenv.
+ * Do not use fldcw as it can generate pending floating-point exception.
+ */
+ if (oldsw != newsw || oldcw != newcw)
{
- struct {
- WORD control_word;
- WORD unused1;
- WORD status_word;
- WORD unused2;
- WORD tag_word;
- WORD unused3;
- DWORD instruction_pointer;
- WORD code_segment;
- WORD unused4;
- DWORD operand_addr;
- WORD data_segment;
- WORD unused5;
- } fenv;
-
- __asm__ __volatile__( "fnstenv %0" : "=m" (fenv) );
fenv.control_word = newcw;
fenv.status_word = newsw;
__asm__ __volatile__( "fldenv %0" : : "m" (fenv) : "st", "st(1)",
"st(2)", "st(3)", "st(4)", "st(5)", "st(6)", "st(7)" );
- return;
}
-
- if (oldsw != newsw)
- __asm__ __volatile__( "fnclex" );
- if (oldcw != newcw)
- __asm__ __volatile__( "fldcw %0" : : "m" (newcw) );
#elif defined(__aarch64__)
ULONG_PTR old_fpsr = 0, fpsr = 0, old_fpcr = 0, fpcr = 0;
unsigned int flags;
--
2.20.1
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