[PATCH] rs6000: Entry point generation for functions using PC-relative addressing

[Bill Schmidt]

Hi,

Functions using PC-relative addressing do not use a TOC, so there is no need for
a global entry point for TOC setup.  Ensure we never generate a global entry
point, and use a .localentry directive that sets the upper st_other bits to 1.

Bootstrapped and tested on powerpc64le-unknown-linux-gnu with no regressions.
Is this okay for trunk?

Thanks,
Bill


[gcc]

2019-05-22  Bill Schmidt  <wschm...@linux.ibm.com>

        * config/rs6000/rs6000.c (rs6000_global_entry_point_needed_p):
        Return false for PC-relative functions.
        (rs6000_output_function_prologue): Emit ".localentry name,1" for
        PC-relative functions.

[gcc/testsuite]

2019-05-22  Bill Schmidt  <wschm...@linux.ibm.com>

        * gcc.target/powerpc/localentry-1.c: New file.


diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
index 959e222c9cb..23c6d37ab55 100644
--- a/gcc/config/rs6000/rs6000.c
+++ b/gcc/config/rs6000/rs6000.c
@@ -26191,6 +26191,10 @@ rs6000_global_entry_point_needed_p (void)
   if (TARGET_SINGLE_PIC_BASE)
     return false;
 
+  /* PC-relative functions never generate a global entry point prologue.  */
+  if (rs6000_pcrel_p (cfun))
+    return false;
+
   /* Ensure we have a global entry point for thunks.   ??? We could
      avoid that if the target routine doesn't need a global entry point,
      but we do not know whether this is the case at this point.  */
@@ -27545,12 +27549,12 @@ rs6000_output_function_prologue (FILE *file)
 #endif
     }
 
+  const char *name = XSTR (XEXP (DECL_RTL (current_function_decl), 0), 0);
+
   /* ELFv2 ABI r2 setup code and local entry point.  This must follow
      immediately after the global entry point label.  */
   if (rs6000_global_entry_point_needed_p ())
     {
-      const char *name = XSTR (XEXP (DECL_RTL (current_function_decl), 0), 0);
-
       (*targetm.asm_out.internal_label) (file, "LCF", rs6000_pic_labelno);
 
       if (TARGET_CMODEL != CMODEL_LARGE)
@@ -27601,6 +27605,18 @@ rs6000_output_function_prologue (FILE *file)
       fputs ("\n", file);
     }
 
+  else if (rs6000_pcrel_p (cfun))
+    {
+      /* All functions compiled to use PC-relative addressing will
+        have a .localentry value of 0 or 1.  For now we set it to
+        1 all the time, indicating that the function may clobber
+        the TOC register r2.  Later we may optimize this by setting
+        it to 0 if the function is a leaf and does not clobber r2.  */
+      fputs ("\t.localentry\t", file);
+      assemble_name (file, name);
+      fputs (",1\n", file);
+    }
+
   /* Output -mprofile-kernel code.  This needs to be done here instead of
      in output_function_profile since it must go after the ELFv2 ABI
      local entry point.  */
diff --git a/gcc/testsuite/gcc.target/powerpc/localentry-1.c 
b/gcc/testsuite/gcc.target/powerpc/localentry-1.c
new file mode 100644
index 00000000000..15e00d9917e
--- /dev/null
+++ b/gcc/testsuite/gcc.target/powerpc/localentry-1.c
@@ -0,0 +1,19 @@
+/* { dg-do compile } */
+/* { dg-options "-mcpu=future -O2" } */
+/* { dg-require-effective-target powerpc_elfv2 } */
+/* { dg-skip-if "do not override -mcpu" { powerpc*-*-* } { "-mcpu=*" } { 
"-mcpu=future" } } */
+
+/* Ensure we generate ".localentry fn,1" for both leaf and non-leaf
+   functions.  */
+
+extern int y (int);
+
+int x (void)
+{
+  return y (5);
+}
+
+void z (void) { };
+
+/* { dg-final { scan-assembler {\.localentry\t\mx,1\M} } } */
+/* { dg-final { scan-assembler {\.localentry\t\mz,1\M} } } */