[gcc r11-10865] rs6000: Don't use TFmode for 128 bits fp constant in toc [PR110011]

[Kewen Lin <linkw@gcc.gnu.org>]

https://gcc.gnu.org/g:bccc9960eb728bfd890c9388593bd166efcd0591

commit r11-10865-gbccc9960eb728bfd890c9388593bd166efcd0591
Author: Kewen Lin <linkw@linux.ibm.com>
Date:   Mon Jun 12 01:07:52 2023 -0500

    rs6000: Don't use TFmode for 128 bits fp constant in toc [PR110011]
    
    As PR110011 shows, when encoding 128 bits fp constant into
    toc, we adopts REAL_VALUE_TO_TARGET_LONG_DOUBLE which is
    to find the first float mode with LONG_DOUBLE_TYPE_SIZE
    bits of precision, it would be TFmode here.  But the 128
    bits fp constant can be with mode IFmode or KFmode, which
    doesn't necessarily have the same underlying float format
    as the one of TFmode, like this PR exposes, with option
    -mabi=ibmlongdouble TFmode has ibm_extended_format while
    KFmode has ieee_quad_format, mixing up the formats (the
    encoding/decoding ways) would cause unexpected results.
    
    This patch is to make it use constant's own mode instead
    of TFmode for real_to_target call.
    
            PR target/110011
    
    gcc/ChangeLog:
    
            * config/rs6000/rs6000.c (output_toc): Use the mode of the 128-bit
            floating constant itself for real_to_target call.
    
    gcc/testsuite/ChangeLog:
    
            * gcc.target/powerpc/pr110011.c: New test.
    
    (cherry picked from commit 388809f2afde874180da0669c669e241037eeba0)

Diff:
---
 gcc/config/rs6000/rs6000.c                  |  2 +-
 gcc/testsuite/gcc.target/powerpc/pr110011.c | 42 +++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
index c3854a931da..ade91e213d4 100644
--- a/gcc/config/rs6000/rs6000.c
+++ b/gcc/config/rs6000/rs6000.c
@@ -17042,7 +17042,7 @@ output_toc (FILE *file, rtx x, int labelno, machine_mode mode)
       if (DECIMAL_FLOAT_MODE_P (GET_MODE (x)))
 	REAL_VALUE_TO_TARGET_DECIMAL128 (*CONST_DOUBLE_REAL_VALUE (x), k);
       else
-	REAL_VALUE_TO_TARGET_LONG_DOUBLE (*CONST_DOUBLE_REAL_VALUE (x), k);
+	real_to_target (k, CONST_DOUBLE_REAL_VALUE (x), GET_MODE (x));
 
       if (TARGET_64BIT)
 	{
diff --git a/gcc/testsuite/gcc.target/powerpc/pr110011.c b/gcc/testsuite/gcc.target/powerpc/pr110011.c
new file mode 100644
index 00000000000..5b04d3e298a
--- /dev/null
+++ b/gcc/testsuite/gcc.target/powerpc/pr110011.c
@@ -0,0 +1,42 @@
+/* { dg-do run } */
+/* { dg-require-effective-target float128_runtime } */
+/* Force long double to be with IBM format here, to verify
+   _Float128 constant still uses its own format (IEEE) for
+   encoding rather than IBM format.  */
+/* { dg-options "-mfp-in-toc -mabi=ibmlongdouble" } */
+/* { dg-add-options float128 } */
+
+#define MPFR_FLOAT128_MAX 0x1.ffffffffffffffffffffffffffffp+16383f128
+
+__attribute__ ((noipa))
+_Float128 f128_max ()
+{
+  return MPFR_FLOAT128_MAX;
+}
+
+typedef union
+{
+  int w[4];
+  _Float128 f128;
+} U;
+
+int main ()
+{
+
+  U umax;
+  umax.f128 = f128_max ();
+  /* ieee float128 max:
+     7ffeffff ffffffff ffffffff ffffffff.  */
+  if (umax.w[1] != 0xffffffff || umax.w[2] != 0xffffffff)
+    __builtin_abort ();
+#ifdef __LITTLE_ENDIAN__
+  if (umax.w[0] != 0xffffffff || umax.w[3] != 0x7ffeffff)
+    __builtin_abort ();
+#else
+  if (umax.w[3] != 0xffffffff || umax.w[0] != 0x7ffeffff)
+    __builtin_abort ();
+#endif
+
+  return 0;
+}
+