math: adjust compilation flags, use them when testing

We were using special compilation flags for the math package, but we
    weren't using them when testing.  That meant that our tests were not
    checking the real code we were providing.  Fix that.
    
    Fixing that revealed that we were not using a good set of flags, or at
    least were not using flags that let the tests pass.  Adjust the flags
    to stop using -funsafe-math-optimizations on x86.  Instead always use
    -ffp-contract=off -fno-math-errno -fno-trapping-math for all targets.
    
    Fixes golang/go#23647
    
    Reviewed-on: https://go-review.googlesource.com/91355

From-SVN: r257312

libgo/Makefile.am

@@ -1138,6 +1138,7 @@ $(foreach package,$(GOTOOL_PACKAGES),$(eval $(call PACKAGE_template,$(package)))
 # Pass -ffp-contract=off, or 386-specific options, when building the
 # math package.  MATH_FLAG is defined in configure.ac.
 math_lo_GOCFLAGS = $(MATH_FLAG)
+math_check_GOCFLAGS = $(MATH_FLAG)
 
 # Add the generated file runtime_sysinfo.go to the runtime package.
 extra_go_files_runtime = runtime_sysinfo.go sigtab.go

libgo/Makefile.in

@@ -1175,6 +1175,7 @@ CHECK_DEPS = $(toolexeclibgo_DATA) $(toolexeclibgoarchive_DATA) \
 # Pass -ffp-contract=off, or 386-specific options, when building the
 # math package.  MATH_FLAG is defined in configure.ac.
 math_lo_GOCFLAGS = $(MATH_FLAG)
+math_check_GOCFLAGS = $(MATH_FLAG)
 
 # Add the generated file runtime_sysinfo.go to the runtime package.
 extra_go_files_runtime = runtime_sysinfo.go sigtab.go

libgo/configure

@@ -15076,10 +15076,9 @@ fi
 $as_echo "$libgo_cv_c_fancymath" >&6; }
 MATH_FLAG=
 if test "$libgo_cv_c_fancymath" = yes; then
-  MATH_FLAG="-mfancy-math-387 -funsafe-math-optimizations -fno-math-errno"
-else
-  MATH_FLAG="-ffp-contract=off"
+  MATH_FLAG="-mfancy-math-387"
 fi
+MATH_FLAG="${MATH_FLAG} -ffp-contract=off -fno-math-errno -fno-trapping-math"
 
 
 CFLAGS_hold=$CFLAGS

libgo/configure.ac

@@ -649,8 +649,7 @@ fi
 AC_SUBST(STRINGOPS_FLAG)
 
 dnl For x86 we want to compile the math library with -mfancy-math-387
-dnl -funsafe-math-optimizations so that we can use the builtin
-dnl instructions directly.
+dnl so that we can use the builtin instructions directly.
 AC_CACHE_CHECK([whether compiler supports -mfancy-math-387],
 [libgo_cv_c_fancymath],
 [CFLAGS_hold=$CFLAGS
@@ -661,10 +660,9 @@ AC_COMPILE_IFELSE([int i;],
 CFLAGS=$CFLAGS_hold])
 MATH_FLAG=
 if test "$libgo_cv_c_fancymath" = yes; then
-  MATH_FLAG="-mfancy-math-387 -funsafe-math-optimizations -fno-math-errno"
-else
-  MATH_FLAG="-ffp-contract=off"
+  MATH_FLAG="-mfancy-math-387"
 fi
+MATH_FLAG="${MATH_FLAG} -ffp-contract=off -fno-math-errno -fno-trapping-math"
 AC_SUBST(MATH_FLAG)
 
 CFLAGS_hold=$CFLAGS

libgo/go/math/all_test.go

@@ -128,7 +128,7 @@ var cbrt = []float64{
 var ceil = []float64{
 	5.0000000000000000e+00,
 	8.0000000000000000e+00,
-	0.0000000000000000e+00,
+	Copysign(0, -1),
 	-5.0000000000000000e+00,
 	1.0000000000000000e+01,
 	3.0000000000000000e+00,
@@ -644,7 +644,7 @@ var tanh = []float64{
 var trunc = []float64{
 	4.0000000000000000e+00,
 	7.0000000000000000e+00,
-	-0.0000000000000000e+00,
+	Copysign(0, -1),
 	-5.0000000000000000e+00,
 	9.0000000000000000e+00,
 	2.0000000000000000e+00,
@@ -2134,7 +2134,7 @@ func TestCbrt(t *testing.T) {
 
 func TestCeil(t *testing.T) {
 	for i := 0; i < len(vf); i++ {
-		if f := Ceil(vf[i]); ceil[i] != f {
+		if f := Ceil(vf[i]); !alike(ceil[i], f) {
 			t.Errorf("Ceil(%g) = %g, want %g", vf[i], f, ceil[i])
 		}
 	}
@@ -2361,7 +2361,7 @@ func TestDim(t *testing.T) {
 
 func TestFloor(t *testing.T) {
 	for i := 0; i < len(vf); i++ {
-		if f := Floor(vf[i]); floor[i] != f {
+		if f := Floor(vf[i]); !alike(floor[i], f) {
 			t.Errorf("Floor(%g) = %g, want %g", vf[i], f, floor[i])
 		}
 	}
@@ -2884,7 +2884,7 @@ func TestTanh(t *testing.T) {
 
 func TestTrunc(t *testing.T) {
 	for i := 0; i < len(vf); i++ {
-		if f := Trunc(vf[i]); trunc[i] != f {
+		if f := Trunc(vf[i]); !alike(trunc[i], f) {
 			t.Errorf("Trunc(%g) = %g, want %g", vf[i], f, trunc[i])
 		}
 	}