expr: Allow same precision modes conversion between {ibm_extended, ieee_quad}_format

With some historical reasons, rs6000 defines KFmode, TFmode
and IFmode to have different mode precisions, but it causes
some issues and needs some workarounds such as PR112993.
So we are going to make all rs6000 128 bit scalar FP modes
have 128 bit precision.  Be prepared for that, this patch
is to make function convert_mode_scalar allow same precision
FP modes conversion if their underlying formats are
ibm_extended_format and ieee_quad_format respectively, just
like the existing special treatment on arm_bfloat_half_format
<-> ieee_half_format.  It also factors out all the relevant
checks into a lambda function.  Besides, similar to ieee fp16
-> bfloat conversion, it adopts trunc_optab rather than
sext_optab for ibm128 to ieee128 conversion.

	PR target/112993

gcc/ChangeLog:

	* expr.cc (convert_mode_scalar): Allow same precision conversion
	between scalar floating point modes if whose underlying format is
	ibm_extended_format or ieee_quad_format, and refactor assertion
	with new lambda function acceptable_same_precision_modes.  Use
	trunc_optab rather than sext_optab for ibm128 to ieee128 conversion.
	* optabs-libfuncs.cc (gen_trunc_conv_libfunc): Use trunc_optab rather
	than sext_optab for ibm128 to ieee128 conversion.

2 files changed, 33 insertions, 10 deletions

diff --git a/gcc/expr.cc b/gcc/expr.cc
index ffbac51..2089c2b 100644
--- a/gcc/expr.cc
+++ b/gcc/expr.cc
@@ -338,6 +338,29 @@ convert_mode_scalar (rtx to, rtx from, int unsignedp)
   enum rtx_code equiv_code = (unsignedp < 0 ? UNKNOWN
 			      : (unsignedp ? ZERO_EXTEND : SIGN_EXTEND));
 
+  auto acceptable_same_precision_modes
+    = [] (scalar_mode from_mode, scalar_mode to_mode) -> bool
+    {
+      if (DECIMAL_FLOAT_MODE_P (from_mode) != DECIMAL_FLOAT_MODE_P (to_mode))
+	return true;
+
+      /* arm_bfloat_half_format <-> ieee_half_format */
+      if ((REAL_MODE_FORMAT (from_mode) == &arm_bfloat_half_format
+	   && REAL_MODE_FORMAT (to_mode) == &ieee_half_format)
+	  || (REAL_MODE_FORMAT (to_mode) == &arm_bfloat_half_format
+	      && REAL_MODE_FORMAT (from_mode) == &ieee_half_format))
+	return true;
+
+      /* ibm_extended_format <-> ieee_quad_format */
+      if ((REAL_MODE_FORMAT (from_mode) == &ibm_extended_format
+	   && REAL_MODE_FORMAT (to_mode) == &ieee_quad_format)
+	  || (REAL_MODE_FORMAT (from_mode) == &ieee_quad_format
+	      && REAL_MODE_FORMAT (to_mode) == &ibm_extended_format))
+	return true;
+
+      return false;
+    };
+
   if (to_real)
     {
       rtx value;
@@ -346,18 +369,16 @@ convert_mode_scalar (rtx to, rtx from, int unsignedp)
 
       gcc_assert ((GET_MODE_PRECISION (from_mode)
 		   != GET_MODE_PRECISION (to_mode))
-		  || (DECIMAL_FLOAT_MODE_P (from_mode)
-		      != DECIMAL_FLOAT_MODE_P (to_mode))
-		  || (REAL_MODE_FORMAT (from_mode) == &arm_bfloat_half_format
-		      && REAL_MODE_FORMAT (to_mode) == &ieee_half_format)
-		  || (REAL_MODE_FORMAT (to_mode) == &arm_bfloat_half_format
-		      && REAL_MODE_FORMAT (from_mode) == &ieee_half_format));
+		  || acceptable_same_precision_modes (from_mode, to_mode));
 
       if (GET_MODE_PRECISION (from_mode) == GET_MODE_PRECISION (to_mode))
 	{
-	  if (REAL_MODE_FORMAT (to_mode) == &arm_bfloat_half_format
-	      && REAL_MODE_FORMAT (from_mode) == &ieee_half_format)
-	    /* libgcc implements just __trunchfbf2, not __extendhfbf2.  */
+	  if ((REAL_MODE_FORMAT (to_mode) == &arm_bfloat_half_format
+	       && REAL_MODE_FORMAT (from_mode) == &ieee_half_format)
+	      || (REAL_MODE_FORMAT (to_mode) == &ieee_quad_format
+		  && REAL_MODE_FORMAT (from_mode) == &ibm_extended_format))
+	    /* libgcc implements just __trunchfbf2, not __extendhfbf2;
+	       and __trunctfkf2, not __extendtfkf2.  */
 	    tab = trunc_optab;
 	  else
 	    /* Conversion between decimal float and binary float, same
diff --git a/gcc/optabs-libfuncs.cc b/gcc/optabs-libfuncs.cc
index 2672991..ab97eac 100644
--- a/gcc/optabs-libfuncs.cc
+++ b/gcc/optabs-libfuncs.cc
@@ -591,7 +591,9 @@ gen_trunc_conv_libfunc (convert_optab tab,
 
   if (GET_MODE_PRECISION (float_fmode) <= GET_MODE_PRECISION (float_tmode)
       && (REAL_MODE_FORMAT (float_tmode) != &arm_bfloat_half_format
-	  || REAL_MODE_FORMAT (float_fmode) != &ieee_half_format))
+	  || REAL_MODE_FORMAT (float_fmode) != &ieee_half_format)
+      && (REAL_MODE_FORMAT (float_tmode) != &ieee_quad_format
+	  || REAL_MODE_FORMAT (float_fmode) != &ibm_extended_format))
     return;
 
   if (GET_MODE_CLASS (float_tmode) == GET_MODE_CLASS (float_fmode))