From: Richard Lowe <richlowe@richlowe.net>
Date: Sat, 27 Oct 2012 02:44:09 +0100
Subject: [PATCH] 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.

See http://wiki.illumos.org/display/illumos/GCC+Modifications

Index: gcc-9.git/src/gcc/common.opt
===================================================================
--- gcc-9.git.orig/src/gcc/common.opt
+++ gcc-9.git/src/gcc/common.opt
@@ -2499,6 +2499,10 @@ fstrict-aliasing
 Common Report Var(flag_strict_aliasing) Optimization
 Assume strict aliasing rules apply.
 
+fstrict-calling-conventions
+Common Report Var(flag_strict_calling_conventions) Init(1)
+Use strict ABI calling conventions even for static functions
+
 fstrict-overflow
 Common Report
 Treat signed overflow as undefined.  Negated as -fwrapv -fwrapv-pointer.
Index: gcc-9.git/src/gcc/config/i386/i386.c
===================================================================
--- gcc-9.git.orig/src/gcc/config/i386/i386.c
+++ gcc-9.git/src/gcc/config/i386/i386.c
@@ -6608,6 +6608,7 @@ ix86_function_regparm (const_tree type,
 
   /* Use register calling convention for local functions when possible.  */
   if (decl
+      && (TARGET_64BIT || !flag_strict_calling_conventions)
       && TREE_CODE (decl) == FUNCTION_DECL)
     {
       cgraph_node *target = cgraph_node::get (decl);
@@ -6717,6 +6718,7 @@ ix86_function_sseregparm (const_tree typ
       /* TARGET_SSE_MATH */
       && (target_opts_for_fn (target->decl)->x_ix86_fpmath & FPMATH_SSE)
       && opt_for_fn (target->decl, optimize)
+      && (TARGET_64BIT || !flag_strict_calling_conventions)
       && !(profile_flag && !flag_fentry))
     {
       cgraph_local_info *i = &target->local;
Index: gcc-9.git/src/gcc/doc/invoke.texi
===================================================================
--- gcc-9.git.orig/src/gcc/doc/invoke.texi
+++ gcc-9.git/src/gcc/doc/invoke.texi
@@ -13756,6 +13756,12 @@ overflow on addition and subtraction wra
 representation.  This flag disables some optimizations which assume
 pointer overflow is invalid.
 
+@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 -fstrict-overflow
 @opindex fstrict-overflow
 This option implies @option{-fno-wrapv} @option{-fno-wrapv-pointer} and when
Index: gcc-9.git/src/gcc/testsuite/gcc.target/i386/local.c
===================================================================
--- gcc-9.git.orig/src/gcc/testsuite/gcc.target/i386/local.c
+++ gcc-9.git/src/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 ilp32 } } */
+/* { 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 } } } } */
 
Index: gcc-9.git/src/gcc/testsuite/gcc.target/i386/strict-cc.c
===================================================================
--- /dev/null
+++ gcc-9.git/src/gcc/testsuite/gcc.target/i386/strict-cc.c
@@ -0,0 +1,22 @@
+/* { 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 t(int, int, int, int, int) __attribute__ ((noinline));
+
+m()
+{
+    t(1, 2, 3, 4, 5);
+}
+
+static t(int a, int b, int c, int d, int e)
+{
+    printf("%d\n", a, b, c, d, e);
+}