i386: Fix unsigned int -> double conversion on i386 w/ -mfpmath=sse [PR100119]

2021-04-22  Uroš Bizjak  <ubizjak@gmail.com>

gcc/
	PR target/100119
	* config/i386/i386-expand.c (ix86_expand_convert_uns_sidf_sse):
	Remove the sign with FE_DOWNWARD, where x - x = -0.0.

gcc/testsuite/

	PR target/100119
	* gcc.target/i386/pr100119.c: New test.

2 files changed, 35 insertions, 0 deletions

diff --git a/gcc/config/i386/i386-expand.c b/gcc/config/i386/i386-expand.c
index 166c23d..516440e 100644
--- a/gcc/config/i386/i386-expand.c
+++ b/gcc/config/i386/i386-expand.c
@@ -1550,6 +1550,8 @@ ix86_expand_convert_uns_sixf_sse (rtx, rtx)
   gcc_unreachable ();
 }
 
+static rtx ix86_expand_sse_fabs (rtx op0, rtx *smask);
+
 /* Convert an unsigned SImode value into a DFmode.  Only currently used
    for SSE, but applicable anywhere.  */
 
@@ -1569,6 +1571,11 @@ ix86_expand_convert_uns_sidf_sse (rtx target, rtx input)
   x = const_double_from_real_value (TWO31r, DFmode);
 
   x = expand_simple_binop (DFmode, PLUS, fp, x, target, 0, OPTAB_DIRECT);
+
+  /* Remove the sign with FE_DOWNWARD, where x - x = -0.0.  */
+  if (HONOR_SIGNED_ZEROS (DFmode) && flag_rounding_math)
+    x = ix86_expand_sse_fabs (x, NULL);
+
   if (x != target)
     emit_move_insn (target, x);
 }
diff --git a/gcc/testsuite/gcc.target/i386/pr100119.c b/gcc/testsuite/gcc.target/i386/pr100119.c
new file mode 100644
index 0000000..be9472e
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr100119.c
@@ -0,0 +1,28 @@
+/* PR target/100119 */
+/* { dg-do run { target sse2_runtime } } */
+/* { dg-require-effective-target fenv } */
+/* { dg-options "-O2 -frounding-math -msse2 -mno-avx512f -mfpmath=sse" } */
+
+#include <fenv.h>
+
+double
+__attribute__((noinline))
+test (unsigned int x)
+{
+  return x;
+}
+
+int
+main ()
+{
+  double result;
+
+  fesetround (FE_DOWNWARD);
+
+  result = test (0);
+
+  if (__builtin_signbit (result) != 0)
+    __builtin_abort ();
+
+  return 0;
+}