commit e5e0d9a4f632735cf3bb440eecb5caee5eea44c1
Author: Ian Bolton <ian.bolton@arm.com>
Date:   Thu Apr 24 07:15:33 2014 +0100

    [AArch64] Suppress unnecessary FPSR and FPCR writes.

diff --git a/ports/sysdeps/aarch64/fpu/fclrexcpt.c b/ports/sysdeps/aarch64/fpu/fclrexcpt.c
index 531269f..b24f0ff 100644
--- a/ports/sysdeps/aarch64/fpu/fclrexcpt.c
+++ b/ports/sysdeps/aarch64/fpu/fclrexcpt.c
@@ -23,13 +23,15 @@ int
 feclearexcept (int excepts)
 {
   fpu_fpsr_t fpsr;
+  fpu_fpsr_t fpsr_new;
 
   excepts &= FE_ALL_EXCEPT;
 
   _FPU_GETFPSR (fpsr);
-  fpsr = (fpsr & ~FE_ALL_EXCEPT) | (fpsr & FE_ALL_EXCEPT & ~excepts);
+  fpsr_new = (fpsr & ~FE_ALL_EXCEPT) | (fpsr & FE_ALL_EXCEPT & ~excepts);
 
-  _FPU_SETFPSR (fpsr);
+  if (fpsr != fpsr_new)
+    _FPU_SETFPSR (fpsr_new);
 
   return 0;
 }
diff --git a/ports/sysdeps/aarch64/fpu/fedisblxcpt.c b/ports/sysdeps/aarch64/fpu/fedisblxcpt.c
index 719d52f..c43335c 100644
--- a/ports/sysdeps/aarch64/fpu/fedisblxcpt.c
+++ b/ports/sysdeps/aarch64/fpu/fedisblxcpt.c
@@ -23,6 +23,7 @@ int
 fedisableexcept (int excepts)
 {
   fpu_control_t fpcr;
+  fpu_control_t fpcr_new;
   int original_excepts;
 
   _FPU_GETCW (fpcr);
@@ -31,9 +32,10 @@ fedisableexcept (int excepts)
 
   excepts &= FE_ALL_EXCEPT;
 
-  fpcr &= ~(excepts << FE_EXCEPT_SHIFT);
+  fpcr_new = fpcr & ~(excepts << FE_EXCEPT_SHIFT);
 
-  _FPU_SETCW (fpcr);
+  if (fpcr != fpcr_new)
+    _FPU_SETCW (fpcr_new);
 
   return original_excepts;
 }
diff --git a/ports/sysdeps/aarch64/fpu/feenablxcpt.c b/ports/sysdeps/aarch64/fpu/feenablxcpt.c
index 07a4bbb..70e413c 100644
--- a/ports/sysdeps/aarch64/fpu/feenablxcpt.c
+++ b/ports/sysdeps/aarch64/fpu/feenablxcpt.c
@@ -23,6 +23,7 @@ int
 feenableexcept (int excepts)
 {
   fpu_control_t fpcr;
+  fpu_control_t fpcr_new;
   int original_excepts;
 
   _FPU_GETCW (fpcr);
@@ -31,9 +32,10 @@ feenableexcept (int excepts)
 
   excepts &= FE_ALL_EXCEPT;
 
-  fpcr |= (excepts << FE_EXCEPT_SHIFT);
+  fpcr_new = fpcr | (excepts << FE_EXCEPT_SHIFT);
 
-  _FPU_SETCW (fpcr);
+  if (fpcr != fpcr_new)
+    _FPU_SETCW (fpcr_new);
 
   /* Trapping exceptions are optional in AArch64 the relevant enable
      bits in FPCR are RES0 hence the absence of support can be
diff --git a/ports/sysdeps/aarch64/fpu/feholdexcpt.c b/ports/sysdeps/aarch64/fpu/feholdexcpt.c
index 0514ac1..973ba4a 100644
--- a/ports/sysdeps/aarch64/fpu/feholdexcpt.c
+++ b/ports/sysdeps/aarch64/fpu/feholdexcpt.c
@@ -22,8 +22,10 @@
 int
 feholdexcept (fenv_t *envp)
 {
-  fpu_fpsr_t fpsr;
   fpu_control_t fpcr;
+  fpu_control_t fpcr_new;
+  fpu_fpsr_t fpsr;
+  fpu_fpsr_t fpsr_new;
 
   _FPU_GETCW (fpcr);
   envp->__fpcr = fpcr;
@@ -32,14 +34,16 @@ feholdexcept (fenv_t *envp)
   envp->__fpsr = fpsr;
 
   /* Now set all exceptions to non-stop.  */
-  fpcr &= ~(FE_ALL_EXCEPT << FE_EXCEPT_SHIFT);
+  fpcr_new = fpcr & ~(FE_ALL_EXCEPT << FE_EXCEPT_SHIFT);
 
   /* And clear all exception flags.  */
-  fpsr &= ~FE_ALL_EXCEPT;
+  fpsr_new = fpsr & ~FE_ALL_EXCEPT;
 
-  _FPU_SETFPSR (fpsr);
+  if (fpsr != fpsr_new)
+    _FPU_SETFPSR (fpsr_new);
 
-  _FPU_SETCW (fpcr);
+  if (fpcr != fpcr_new)
+    _FPU_SETCW (fpcr_new);
 
   return 0;
 }
diff --git a/ports/sysdeps/aarch64/fpu/fesetenv.c b/ports/sysdeps/aarch64/fpu/fesetenv.c
index a2434e3..30193e9 100644
--- a/ports/sysdeps/aarch64/fpu/fesetenv.c
+++ b/ports/sysdeps/aarch64/fpu/fesetenv.c
@@ -23,34 +23,38 @@ int
 fesetenv (const fenv_t *envp)
 {
   fpu_control_t fpcr;
-  fpu_fpsr_t fpsr;
+  fpu_control_t fpcr_new;
   fpu_control_t updated_fpcr;
+  fpu_fpsr_t fpsr;
+  fpu_fpsr_t fpsr_new;
 
   _FPU_GETCW (fpcr);
   _FPU_GETFPSR (fpsr);
 
-  fpcr &= _FPU_RESERVED;
-  fpsr &= _FPU_FPSR_RESERVED;
+  fpcr_new = fpcr & _FPU_RESERVED;
+  fpsr_new = fpsr & _FPU_FPSR_RESERVED;
 
   if (envp == FE_DFL_ENV)
     {
-      fpcr |= _FPU_DEFAULT;
-      fpsr |= _FPU_FPSR_DEFAULT;
+      fpcr_new |= _FPU_DEFAULT;
+      fpsr_new |= _FPU_FPSR_DEFAULT;
     }
   else if (envp == FE_NOMASK_ENV)
     {
-      fpcr |= _FPU_FPCR_IEEE;
-      fpsr |= _FPU_FPSR_IEEE;
+      fpcr_new |= _FPU_FPCR_IEEE;
+      fpsr_new |= _FPU_FPSR_IEEE;
     }
   else
     {
-      fpcr |= envp->__fpcr & ~_FPU_RESERVED;
-      fpsr |= envp->__fpsr & ~_FPU_FPSR_RESERVED;
+      fpcr_new |= envp->__fpcr & ~_FPU_RESERVED;
+      fpsr_new |= envp->__fpsr & ~_FPU_FPSR_RESERVED;
     }
 
-  _FPU_SETFPSR (fpsr);
+  if (fpsr != fpsr_new)
+    _FPU_SETFPSR (fpsr_new);
 
-  _FPU_SETCW (fpcr);
+  if (fpcr != fpcr_new)
+    _FPU_SETCW (fpcr_new);
 
   /* Trapping exceptions are optional in AArch64 the relevant enable
      bits in FPCR are RES0 hence the absence of support can be
@@ -58,7 +62,7 @@ fesetenv (const fenv_t *envp)
      value.  */
 
   _FPU_GETCW (updated_fpcr);
-  if ((updated_fpcr & fpcr) != fpcr)
+  if ((updated_fpcr & fpcr_new) != fpcr_new)
     return 1;
 
   return 0;
diff --git a/ports/sysdeps/aarch64/fpu/fesetround.c b/ports/sysdeps/aarch64/fpu/fesetround.c
index 40a05f6..225096a 100644
--- a/ports/sysdeps/aarch64/fpu/fesetround.c
+++ b/ports/sysdeps/aarch64/fpu/fesetround.c
@@ -23,6 +23,7 @@ int
 fesetround (int round)
 {
   fpu_control_t fpcr;
+  fpu_control_t fpcr_new;
 
   switch (round)
     {
@@ -31,9 +32,10 @@ fesetround (int round)
     case FE_DOWNWARD:
     case FE_TOWARDZERO:
       _FPU_GETCW (fpcr);
-      fpcr = (fpcr & ~FE_TOWARDZERO) | round;
+      fpcr_new = (fpcr & ~FE_TOWARDZERO) | round;
 
-      _FPU_SETCW (fpcr);
+      if (fpcr != fpcr_new)
+	_FPU_SETCW (fpcr_new);
       return 0;
 
     default:
diff --git a/ports/sysdeps/aarch64/fpu/fsetexcptflg.c b/ports/sysdeps/aarch64/fpu/fsetexcptflg.c
index 49cd1e4..60bb1c9 100644
--- a/ports/sysdeps/aarch64/fpu/fsetexcptflg.c
+++ b/ports/sysdeps/aarch64/fpu/fsetexcptflg.c
@@ -24,16 +24,18 @@ int
 fesetexceptflag (const fexcept_t *flagp, int excepts)
 {
   fpu_fpsr_t fpsr;
+  fpu_fpsr_t fpsr_new;
 
   /* Get the current environment.  */
   _FPU_GETFPSR (fpsr);
 
   /* Set the desired exception mask.  */
-  fpsr &= ~(excepts & FE_ALL_EXCEPT);
-  fpsr |= (*flagp & excepts & FE_ALL_EXCEPT);
+  fpsr_new = fpsr & ~(excepts & FE_ALL_EXCEPT);
+  fpsr_new |= (*flagp & excepts & FE_ALL_EXCEPT);
 
   /* Save state back to the FPU.  */
-  _FPU_SETFPSR (fpsr);
+  if (fpsr != fpsr_new)
+    _FPU_SETFPSR (fpsr_new);
 
   return 0;
 }