i386: Enable -mnop-mcount for -fpic with PLTs [PR119386]

-mnop-mcount can be trivially enabled for -fPIC codegen as long as PLTs
are being used, given that the instruction encodings are identical, only
the target may resolve differently depending on how the linker decides
to incorporate the object file.

So relax the option check, and add a test to ensure that 5-byte NOPs are
emitted when -mnop-mcount is being used.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
gcc/ChangeLog:

	PR target/119386
	* config/i386/i386-options.cc: Permit -mnop-mcount when
	using -fpic with PLTs.

gcc/testsuite/ChangeLog:

	PR target/119386
	* gcc.target/i386/pr119386-3.c: New test.

(cherry picked from commit 6b4569a3ebdd0df44d87d67a18272ec0b878f2ee)

diff --git a/gcc/config/i386/i386-options.cc b/gcc/config/i386/i386-options.cc
index 57c83a9aa1c7298358cb8f9ccbd1a89b71c984cc..81dd217ab7270a68c10aee1ab79f2b1ddffbd32b 100644 (file)
--- a/gcc/config/i386/i386-options.cc
+++ b/gcc/config/i386/i386-options.cc
@@ -2842,8 +2842,8 @@ ix86_option_override_internal (bool main_args_p,
   if (flag_nop_mcount)
     error ("%<-mnop-mcount%> is not compatible with this target");
 #endif
-  if (flag_nop_mcount && flag_pic)
-    error ("%<-mnop-mcount%> is not implemented for %<-fPIC%>");
+  if (flag_nop_mcount && flag_pic && !flag_plt)
+    error ("%<-mnop-mcount%> is not implemented for %<-fno-plt%>");
 
   /* Accept -msseregparm only if at least SSE support is enabled.  */
   if (TARGET_SSEREGPARM_P (opts->x_target_flags)

diff --git a/gcc/testsuite/gcc.target/i386/pr119386-3.c b/gcc/testsuite/gcc.target/i386/pr119386-3.c
new file mode 100644 (file)
index 0000000..287410b
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr119386-3.c
@@ -0,0 +1,10 @@
+/* PR target/119386 */
+/* { dg-do compile { target *-*-linux* } } */
+/* { dg-options "-O2 -fpic -pg -mnop-mcount" } */
+/* { dg-final { scan-assembler ".byte\[ \t\]+0x0f, 0x1f, 0x44, 0x00, 0x00" } } */
+
+int
+main ()
+{
+  return 0;
+}