floorf, ceilf tests: Strengthen against compiler optimizations

[Bruno Haible]

René Rebe noticed that in a slightly modified version of test-floorf-ieee.c,
"gcc -O2" inlines the 'floorf' function, despite the conditional expression
initializer. The test is pointless with this inlining. This patch provides
a defense against it.


2023-11-24  Bruno Haible  <br...@clisp.org>

        floorf, ceilf tests: Strengthen against compiler optimizations.
        Reported by René Rebe <r...@t2-project.org>.
        * tests/test-floorf1.c (main): Mark my_floorf as 'volatile'.
        * tests/test-floorf-ieee.c (main): Likewise.
        * tests/test-ceilf1.c (main): Mark my_ceilf as 'volatile'.
        * tests/test-ceilf-ieee.c (main): Likewise.

diff --git a/tests/test-ceilf-ieee.c b/tests/test-ceilf-ieee.c
index 02edc0d92a..bfdceee1c5 100644
--- a/tests/test-ceilf-ieee.c
+++ b/tests/test-ceilf-ieee.c
@@ -38,7 +38,7 @@ dummy (float f)
 int
 main (int argc, _GL_UNUSED char **argv)
 {
-  float (*my_ceilf) (float) = argc ? ceilf : dummy;
+  float (* volatile my_ceilf) (float) = argc ? ceilf : dummy;
 
   /* See IEEE 754, section 6.3:
        "the sign of the result of the round floating-point number to
diff --git a/tests/test-ceilf1.c b/tests/test-ceilf1.c
index 61a4ae99b5..2ad2b30fb0 100644
--- a/tests/test-ceilf1.c
+++ b/tests/test-ceilf1.c
@@ -43,7 +43,7 @@ dummy (float f)
 int
 main (int argc, _GL_UNUSED char **argv)
 {
-  float (*my_ceilf) (float) = argc ? ceilf : dummy;
+  float (* volatile my_ceilf) (float) = argc ? ceilf : dummy;
 
   /* Zero.  */
   ASSERT (my_ceilf (0.0f) == 0.0f);
diff --git a/tests/test-floorf-ieee.c b/tests/test-floorf-ieee.c
index 32ceb5b7b1..8b1a02ac89 100644
--- a/tests/test-floorf-ieee.c
+++ b/tests/test-floorf-ieee.c
@@ -38,7 +38,7 @@ dummy (float f)
 int
 main (int argc, _GL_UNUSED char **argv)
 {
-  float (*my_floorf) (float) = argc ? floorf : dummy;
+  float (* volatile my_floorf) (float) = argc ? floorf : dummy;
 
   /* See IEEE 754, section 6.3:
        "the sign of the result of the round floating-point number to
diff --git a/tests/test-floorf1.c b/tests/test-floorf1.c
index b2787f6ff3..39b7a48432 100644
--- a/tests/test-floorf1.c
+++ b/tests/test-floorf1.c
@@ -43,7 +43,7 @@ dummy (float f)
 int
 main (int argc, _GL_UNUSED char **argv)
 {
-  float (*my_floorf) (float) = argc ? floorf : dummy;
+  float (* volatile my_floorf) (float) = argc ? floorf : dummy;
 
   /* Zero.  */
   ASSERT (my_floorf (0.0f) == 0.0f);