[PATCH] libgccjit: Fix float playback for cross-compilation

[Antoni Boucher]

Hi.
This patch fixes the bug 113343.
I'm wondering if there's a better solution than using mpfr.
The only other solution I found is real_from_string, but that seems
overkill to convert the number to a string.
I could not find a better way to create a real value from a host
double.
If there's no solution, do we lose some precision by using mpfr?
Running Rust's core library tests, there was a difference of one
decimal, so I'm wondering if there's some lost precision, or if it's
just because those tests don't work on m68k which was my test target.
Also, I'm not sure how to write a test this fix. Any ideas?
Thanks for the review.

From 8ddfd4abbe6e46efc256030c2d010f035cd9ecf0 Mon Sep 17 00:00:00 2001
From: Antoni Boucher <boua...@zoho.com>
Date: Sat, 21 Oct 2023 11:20:46 -0400
Subject: [PATCH] libgccjit: Fix float playback for cross-compilation

gcc/jit/ChangeLog:
	PR jit/113343
	* jit-playback.cc (new_rvalue_from_const): Fix to have the
	correct value when cross-compiling.
---
 gcc/jit/jit-playback.cc | 21 ++++++++-------------
 1 file changed, 8 insertions(+), 13 deletions(-)

diff --git a/gcc/jit/jit-playback.cc b/gcc/jit/jit-playback.cc
index dddd537f3b1..9cb27ee4ef3 100644
--- a/gcc/jit/jit-playback.cc
+++ b/gcc/jit/jit-playback.cc
@@ -41,6 +41,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "gcc.h"
 #include "diagnostic.h"
 #include "stmt.h"
+#include "realmpfr.h"
 
 #include "jit-playback.h"
 #include "jit-result.h"
@@ -932,22 +933,16 @@ new_rvalue_from_const <double> (type *type,
   // FIXME: type-checking, or coercion?
   tree inner_type = type->as_tree ();
 
+  mpfr_t mpf_value;
+
+  mpfr_init2 (mpf_value, 64);
+  mpfr_set_d (mpf_value, value, MPFR_RNDN);
+
   /* We have a "double", we want a REAL_VALUE_TYPE.
 
-     real.cc:real_from_target appears to require the representation to be
-     split into 32-bit values, and then sent as an pair of host long
-     ints.  */
+     realmpfr.cc:real_from_mpfr.  */
   REAL_VALUE_TYPE real_value;
-  union
-  {
-    double as_double;
-    uint32_t as_uint32s[2];
-  } u;
-  u.as_double = value;
-  long int as_long_ints[2];
-  as_long_ints[0] = u.as_uint32s[0];
-  as_long_ints[1] = u.as_uint32s[1];
-  real_from_target (&real_value, as_long_ints, DFmode);
+  real_from_mpfr (&real_value, mpf_value, inner_type, MPFR_RNDN);
   tree inner = build_real (inner_type, real_value);
   return new rvalue (this, inner);
 }
-- 
2.43.0