Use ppc_r12 for some global call sequences

After the mechanical exchange of ppc_r11 and ppc_r12 we now can use
ppc_r12 for global calls to hold the callees address without clobbering
r11 (which potentially contains IMT_REG, VTABLE_REG and RGCTX_REG).
We don't need to change all indirect calls, only those potentially reaching
functions containing a TOC setup based on r12 (in particular functions
in shared libs).  As the instruction sequence patcher can only deal
with one destination register we also need to make some additional
calls use r12.  We probably should convert all calls that currently
use r0 to use r12 if no other conflicts arise but this is enough to build.

Index: mono-3.4.0/mono/mini/exceptions-ppc.c
===================================================================
--- mono-3.4.0.orig/mono/mini/exceptions-ppc.c
+++ mono-3.4.0/mono/mini/exceptions-ppc.c
@@ -391,8 +391,8 @@ mono_arch_get_throw_exception_generic (i
 			ppc_bcctrl (code, PPC_BR_ALWAYS, 0);
 		} else {
 			ppc_load (code, ppc_r3, (gulong)mono_defaults.corlib);
-			ppc_load_func (code, ppc_r0, mono_exception_from_token);
-			ppc_mtctr (code, ppc_r0);
+			ppc_load_func (code, PPC_CALL_REG, mono_exception_from_token);
+			ppc_mtctr (code, PPC_CALL_REG);
 			ppc_bcctrl (code, PPC_BR_ALWAYS, 0);
 		}
 	}
@@ -426,8 +426,8 @@ mono_arch_get_throw_exception_generic (i
 		ppc_mtctr (code, ppc_r12);
 		ppc_bcctrl (code, PPC_BR_ALWAYS, 0);
 	} else {
-		ppc_load_func (code, ppc_r0, mono_ppc_throw_exception);
-		ppc_mtctr (code, ppc_r0);
+		ppc_load_func (code, PPC_CALL_REG, mono_ppc_throw_exception);
+		ppc_mtctr (code, PPC_CALL_REG);
 		ppc_bcctrl (code, PPC_BR_ALWAYS, 0);
 	}
 	/* we should never reach this breakpoint */
Index: mono-3.4.0/mono/mini/mini-ppc.c
===================================================================
--- mono-3.4.0.orig/mono/mini/mini-ppc.c
+++ mono-3.4.0/mono/mini/mini-ppc.c
@@ -1782,8 +1782,8 @@ mono_arch_instrument_prolog (MonoCompile
 
 	ppc_load_ptr (code, ppc_r3, cfg->method);
 	ppc_li (code, ppc_r4, 0); /* NULL ebp for now */
-	ppc_load_func (code, ppc_r0, func);
-	ppc_mtlr (code, ppc_r0);
+	ppc_load_func (code, PPC_CALL_REG, func);
+	ppc_mtlr (code, PPC_CALL_REG);
 	ppc_blrl (code);
 	return code;
 }
@@ -1880,8 +1880,8 @@ mono_arch_instrument_epilog_full (MonoCo
 	}
 
 	ppc_load_ptr (code, ppc_r3, cfg->method);
-	ppc_load_func (code, ppc_r0, func);
-	ppc_mtlr (code, ppc_r0);
+	ppc_load_func (code, PPC_CALL_REG, func);
+	ppc_mtlr (code, PPC_CALL_REG);
 	ppc_blrl (code);
 
 	switch (save_mode) {
@@ -2922,7 +2922,7 @@ ppc_patch_full (guchar *code, const guch
 
 			if (!is_fd) {
 				guint8 *buf = (guint8*)&seq [5];
-				ppc_mr (buf, ppc_r0, ppc_r12);
+				ppc_mr (buf, PPC_CALL_REG, ppc_r12);
 				ppc_nop (buf);
 			}
 		} else {
@@ -2935,7 +2935,7 @@ ppc_patch_full (guchar *code, const guch
 		/* FIXME: we're assuming we're using r12 here */
 		ppc_load_ptr_sequence (code, ppc_r12, target);
 #else
-		ppc_load_ptr_sequence (code, ppc_r0, target);
+		ppc_load_ptr_sequence (code, PPC_CALL_REG, target);
 #endif
 		mono_arch_flush_icache ((guint8*)seq, 28);
 #else
@@ -2951,8 +2951,8 @@ ppc_patch_full (guchar *code, const guch
 		g_assert ((seq [2] >> 26) == 31);
 		g_assert (seq [3] == 0x4e800021 || seq [3] == 0x4e800020 || seq [3] == 0x4e800420);
 		/* FIXME: make this thread safe */
-		ppc_lis (code, ppc_r0, (guint32)(target) >> 16);
-		ppc_ori (code, ppc_r0, ppc_r0, (guint32)(target) & 0xffff);
+		ppc_lis (code, PPC_CALL_REG, (guint32)(target) >> 16);
+		ppc_ori (code, PPC_CALL_REG, PPC_CALL_REG, (guint32)(target) & 0xffff);
 		mono_arch_flush_icache (code - 8, 8);
 #endif
 	} else {
@@ -3370,8 +3370,8 @@ mono_arch_output_basic_block (MonoCompil
 			mono_add_patch_info (cfg, code - cfg->native_code, MONO_PATCH_INFO_INTERNAL_METHOD, 
 					     (gpointer)"mono_break");
 			if ((FORCE_INDIR_CALL || cfg->method->dynamic) && !cfg->compile_aot) {
-				ppc_load_func (code, ppc_r0, 0);
-				ppc_mtlr (code, ppc_r0);
+				ppc_load_func (code, PPC_CALL_REG, 0);
+				ppc_mtlr (code, PPC_CALL_REG);
 				ppc_blrl (code);
 			} else {
 				ppc_bl (code, 0);
@@ -3818,8 +3818,8 @@ mono_arch_output_basic_block (MonoCompil
 			else
 				mono_add_patch_info (cfg, offset, MONO_PATCH_INFO_ABS, call->fptr);
 			if ((FORCE_INDIR_CALL || cfg->method->dynamic) && !cfg->compile_aot) {
-				ppc_load_func (code, ppc_r0, 0);
-				ppc_mtlr (code, ppc_r0);
+				ppc_load_func (code, PPC_CALL_REG, 0);
+				ppc_mtlr (code, PPC_CALL_REG);
 				ppc_blrl (code);
 			} else {
 				ppc_bl (code, 0);
@@ -3912,8 +3912,8 @@ mono_arch_output_basic_block (MonoCompil
 			mono_add_patch_info (cfg, code - cfg->native_code, MONO_PATCH_INFO_INTERNAL_METHOD, 
 					     (gpointer)"mono_arch_throw_exception");
 			if ((FORCE_INDIR_CALL || cfg->method->dynamic) && !cfg->compile_aot) {
-				ppc_load_func (code, ppc_r0, 0);
-				ppc_mtlr (code, ppc_r0);
+				ppc_load_func (code, PPC_CALL_REG, 0);
+				ppc_mtlr (code, PPC_CALL_REG);
 				ppc_blrl (code);
 			} else {
 				ppc_bl (code, 0);
@@ -3926,8 +3926,8 @@ mono_arch_output_basic_block (MonoCompil
 			mono_add_patch_info (cfg, code - cfg->native_code, MONO_PATCH_INFO_INTERNAL_METHOD, 
 					     (gpointer)"mono_arch_rethrow_exception");
 			if ((FORCE_INDIR_CALL || cfg->method->dynamic) && !cfg->compile_aot) {
-				ppc_load_func (code, ppc_r0, 0);
-				ppc_mtlr (code, ppc_r0);
+				ppc_load_func (code, PPC_CALL_REG, 0);
+				ppc_mtlr (code, PPC_CALL_REG);
 				ppc_blrl (code);
 			} else {
 				ppc_bl (code, 0);
@@ -5070,8 +5070,8 @@ mono_arch_emit_prolog (MonoCompile *cfg)
 			mono_add_patch_info (cfg, code - cfg->native_code, MONO_PATCH_INFO_INTERNAL_METHOD, 
 				     (gpointer)"mono_get_lmf_addr");
 			if ((FORCE_INDIR_CALL || cfg->method->dynamic) && !cfg->compile_aot) {
-				ppc_load_func (code, ppc_r0, 0);
-				ppc_mtlr (code, ppc_r0);
+				ppc_load_func (code, PPC_CALL_REG, 0);
+				ppc_mtlr (code, PPC_CALL_REG);
 				ppc_blrl (code);
 			} else {
 				ppc_bl (code, 0);
@@ -5380,8 +5380,8 @@ mono_arch_emit_exceptions (MonoCompile *
 			patch_info->data.name = "mono_arch_throw_corlib_exception";
 			patch_info->ip.i = code - cfg->native_code;
 			if (FORCE_INDIR_CALL || cfg->method->dynamic) {
-				ppc_load_func (code, ppc_r0, 0);
-				ppc_mtctr (code, ppc_r0);
+				ppc_load_func (code, PPC_CALL_REG, 0);
+				ppc_mtctr (code, PPC_CALL_REG);
 				ppc_bcctr (code, PPC_BR_ALWAYS, 0);
 			} else {
 				ppc_bl (code, 0);
Index: mono-3.4.0/mono/mini/mini-ppc.h
===================================================================
--- mono-3.4.0.orig/mono/mini/mini-ppc.h
+++ mono-3.4.0/mono/mini/mini-ppc.h
@@ -172,6 +172,8 @@ typedef struct MonoCompileArch {
 #define PPC_FIRST_FPARG_REG ppc_f1
 #endif
 
+#define PPC_CALL_REG ppc_r12
+
 #if defined(HAVE_WORKING_SIGALTSTACK) && !defined(__APPLE__)
 #define MONO_ARCH_SIGSEGV_ON_ALTSTACK 1
 #define MONO_ARCH_SIGNAL_STACK_SIZE (12 * 1024)
Index: mono-3.4.0/mono/mini/tramp-ppc.c
===================================================================
--- mono-3.4.0.orig/mono/mini/tramp-ppc.c
+++ mono-3.4.0/mono/mini/tramp-ppc.c
@@ -306,8 +306,8 @@ mono_arch_create_generic_trampoline (Mon
 		ppc_mtlr (code, ppc_r12);
 		ppc_blrl (code);
 	}  else {
-		ppc_load_func (code, ppc_r0, mono_get_lmf_addr);
-		ppc_mtlr (code, ppc_r0);
+		ppc_load_func (code, PPC_CALL_REG, mono_get_lmf_addr);
+		ppc_mtlr (code, PPC_CALL_REG);
 		ppc_blrl (code);
 	}
 	/* we build the MonoLMF structure on the stack - see mini-ppc.h
@@ -368,8 +368,8 @@ mono_arch_create_generic_trampoline (Mon
 		ppc_blrl (code);
 	} else {
 		tramp_handler = mono_get_trampoline_func (tramp_type);
-		ppc_load_func (code, ppc_r0, tramp_handler);
-		ppc_mtlr (code, ppc_r0);
+		ppc_load_func (code, PPC_CALL_REG, tramp_handler);
+		ppc_mtlr (code, PPC_CALL_REG);
 		ppc_blrl (code);
 	}