From 0c9aef2bfddbd3fc5e856baa4dc2967c5a0c5af3 Mon Sep 17 00:00:00 2001
From: Richard Lowe <richlowe@richlowe.net>
Date: Sat, 27 Oct 2012 02:44:09 +0100
Subject: Implement -fstrict-calling-conventions

Stock GCC is overly willing to violate the ABI when calling local functions,
such that it passes arguments in registers on i386.  This hampers debugging
with anything other than a fully-aware DWARF debugger, and is generally not
something we desire.

Implement a flag which disables this behaviour, enabled by default.  The flag is
global, though only effective on i386, to more easily allow its globalization
later which, given the odds, is likely to be necessary.
---
 gcc/common.opt                            |  4 ++++
 gcc/config/i386/i386.cc                   |  2 ++
 gcc/doc/invoke.texi                       |  6 ++++++
 gcc/testsuite/gcc.target/i386/local.c     |  3 ++-
 gcc/testsuite/gcc.target/i386/strict-cc.c | 24 +++++++++++++++++++++++
 5 files changed, 38 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.target/i386/strict-cc.c

diff --git a/gcc/common.opt b/gcc/common.opt
index 8a0dafc522d..314c1c6a478 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -2745,6 +2745,10 @@ fstrict-aliasing
 Common Var(flag_strict_aliasing) Optimization
 Assume strict aliasing rules apply.
 
+fstrict-calling-conventions
+Common Var(flag_strict_calling_conventions) Init(1)
+Use strict ABI calling conventions even for static functions
+
 fstrict-overflow
 Common
 Treat signed overflow as undefined.  Negated as -fwrapv -fwrapv-pointer.
diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
index 9a9ff3b34b8..ce156c3be3a 100644
--- a/gcc/config/i386/i386.cc
+++ b/gcc/config/i386/i386.cc
@@ -1147,6 +1147,7 @@ ix86_function_regparm (const_tree type, const_tree decl)
 	 and callee not, or vice versa.  Instead look at whether the callee
 	 is optimized or not.  */
       if (target && opt_for_fn (target->decl, optimize)
+	  && !flag_strict_calling_conventions
 	  && !(profile_flag && !flag_fentry))
 	{
 	  if (target->local && target->can_change_signature)
@@ -1243,6 +1244,7 @@ ix86_function_sseregparm (const_tree type, const_tree decl, bool warn)
       /* TARGET_SSE_MATH */
       && (target_opts_for_fn (target->decl)->x_ix86_fpmath & FPMATH_SSE)
       && opt_for_fn (target->decl, optimize)
+      && !flag_strict_calling_conventions
       && !(profile_flag && !flag_fentry))
     {
       if (target->local && target->can_change_signature)
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index cb83dd8a1cc..348df5caf1d 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -7296,6 +7296,12 @@ with multiple statement cases using flow-sensitive points-to information.
 Only warns when the converted pointer is dereferenced.
 Does not warn about incomplete types.
 
+@item -fstrict-calling-conventions
+@opindex fstrict-calling-conventions
+Use strict ABI calling conventions even with local functions.
+This disable certain optimizations that may cause GCC to call local
+functions in a manner other than that described by the ABI.
+
 @item -Wstrict-overflow
 @itemx -Wstrict-overflow=@var{n}
 @opindex Wstrict-overflow
diff --git a/gcc/testsuite/gcc.target/i386/local.c b/gcc/testsuite/gcc.target/i386/local.c
index f4444951e12..3a487583d81 100644
--- a/gcc/testsuite/gcc.target/i386/local.c
+++ b/gcc/testsuite/gcc.target/i386/local.c
@@ -1,5 +1,6 @@
 /* { dg-do compile } */
-/* { dg-options "-O2 -funit-at-a-time" } */
+/* { dg-options "-O2 -funit-at-a-time -fno-strict-calling-conventions" { target ia32 } } */
+/* { dg-options "-O2 -funit-at-a-time" { target lp64 } } */
 /* { dg-final { scan-assembler "magic\[^\\n\]*eax" { target ia32 } } } */
 /* { dg-final { scan-assembler "magic\[^\\n\]*(edi|ecx)" { target { ! ia32 } } } } */
 
diff --git a/gcc/testsuite/gcc.target/i386/strict-cc.c b/gcc/testsuite/gcc.target/i386/strict-cc.c
new file mode 100644
index 00000000000..fa0543e52ff
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/strict-cc.c
@@ -0,0 +1,24 @@
+/* { dg-do compile { target { ilp32 } } } */
+/* { dg-options "-O2 -funit-at-a-time -fstrict-calling-conventions"  } */
+/* { dg-final { scan-assembler "pushl.*\\\$1" } } */
+/* { dg-final { scan-assembler "pushl.*\\\$2" } } */
+/* { dg-final { scan-assembler "pushl.*\\\$3" } } */
+/* { dg-final { scan-assembler "pushl.*\\\$4" } } */
+/* { dg-final { scan-assembler "pushl.*\\\$5" } } */
+
+#include <stdio.h>
+
+/* Verify that local calling convention is not used if strict conventions.  */
+static int t(int, int, int, int, int) __attribute__ ((noinline));
+
+int
+m()
+{
+    t(1, 2, 3, 4, 5);
+}
+
+static int
+t(int a, int b, int c, int d, int e)
+{
+    printf("%d\n", a, b, c, d, e);
+}