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Stop strip_float_extensions removing binary/decimal conversions
- From: "Joseph S. Myers" <joseph at codesourcery dot com>
- To: gcc-patches at gcc dot gnu dot org
- Date: Mon, 27 Oct 2008 22:30:09 +0000 (UTC)
- Subject: Stop strip_float_extensions removing binary/decimal conversions
In the course of looking at various optimizations relating to
floating-point conversions I noticed that strip_float_extensions would
remove not only genuine extensions (conversions preserving all values)
but also conversions between binary and decimal floating-point types,
and that in turn this could cause some optimizations using this
function to perform bad transformations, as illustrated by the test
case added by this patch.
Even with -funsafe-math-optimizations I do not think it makes sense
for the compiler to remove conversions between binary and decimal
floating-point types - or to introduce such conversions, as the code
in strip_float_extensions might have done given a decimal constant
that can be represented in float. This patch unconditionally stops
strip_float_extensions from doing so. Bootstrapped with no
regressions on i686-pc-linux-gnu. OK to commit?
2008-10-27 Joseph Myers <joseph@codesourcery.com>
* convert.c (strip_float_extensions): Do not remove or introduce
conversions between binary and decimal floating-point types.
testsuite:
2008-10-27 Joseph Myers <joseph@codesourcery.com>
* gcc.dg/dfp/convert-bfp-12.c: New test.
Index: convert.c
===================================================================
--- convert.c (revision 141381)
+++ convert.c (working copy)
@@ -81,7 +81,7 @@
it properly and handle it like (type)(narrowest_type)constant.
This way we can optimize for instance a=a*2.0 where "a" is float
but 2.0 is double constant. */
- if (TREE_CODE (exp) == REAL_CST)
+ if (TREE_CODE (exp) == REAL_CST && !DECIMAL_FLOAT_TYPE_P (TREE_TYPE (exp)))
{
REAL_VALUE_TYPE orig;
tree type = NULL;
@@ -108,6 +108,9 @@
if (!FLOAT_TYPE_P (subt))
return exp;
+ if (DECIMAL_FLOAT_TYPE_P (expt) != DECIMAL_FLOAT_TYPE_P (subt))
+ return exp;
+
if (TYPE_PRECISION (subt) > TYPE_PRECISION (expt))
return exp;
Index: testsuite/gcc.dg/dfp/convert-bfp-12.c
===================================================================
--- testsuite/gcc.dg/dfp/convert-bfp-12.c (revision 0)
+++ testsuite/gcc.dg/dfp/convert-bfp-12.c (revision 0)
@@ -0,0 +1,17 @@
+/* Test for bug where fold wrongly removed conversions to double and
+ replaced them by conversions to float. */
+/* { dg-options "-std=gnu99" } */
+
+extern void abort (void);
+extern void exit (int);
+
+volatile float f = __builtin_inff ();
+volatile _Decimal32 d32 = 1e40DF;
+
+int
+main (void)
+{
+ if ((double) f == (double) d32)
+ abort ();
+ exit (0);
+}
--
Joseph S. Myers
joseph@codesourcery.com