Come up with the flag -fipa-stack-alignment.

2018-11-09  Martin Liska  <mliska@suse.cz>

	* common.opt: Add -fipa-stack-alignment flag.
	* doc/invoke.texi: Document it.
	* final.c (rest_of_clean_state): Guard stack
	shrinking with flag.
2018-11-09  Martin Liska  <mliska@suse.cz>

	* gcc.target/i386/ipa-stack-alignment.c: New test.

From-SVN: r265970

gcc/ChangeLog

 2018-11-09  Martin Liska  <mliska@suse.cz>
 
+	* common.opt: Add -fipa-stack-alignment flag.
+	* doc/invoke.texi: Document it.
+	* final.c (rest_of_clean_state): Guard stack
+	shrinking with flag.
+
+2018-11-09  Martin Liska  <mliska@suse.cz>
+
 	* cgraph.h (ipa_discover_readonly_nonaddressable_vars): Rename
 	to ...
 	(ipa_discover_variable_flags): ... this.

gcc/common.opt

@@ -1728,6 +1728,10 @@ fipa-reference-addressable
 Common Report Var(flag_ipa_reference_addressable) Init(0) Optimization
 Discover read-only, write-only and non-addressable static variables.
 
+fipa-stack-alignment
+Common Report Var(flag_ipa_stack_alignment) Init(1) Optimization
+Reduce stack alignment on call sites if possible.
+
 fipa-matrix-reorg
 Common Ignore
 Does nothing. Preserved for backward compatibility.

gcc/doc/invoke.texi

@@ -414,7 +414,7 @@ Objective-C and Objective-C++ Dialects}.
 -finline-small-functions  -fipa-cp  -fipa-cp-clone @gol
 -fipa-bit-cp -fipa-vrp @gol
 -fipa-pta  -fipa-profile  -fipa-pure-const  -fipa-reference  -fipa-reference-addressable @gol
--fipa-icf  -fira-algorithm=@var{algorithm} @gol
+-fipa-stack-alignment  -fipa-icf  -fira-algorithm=@var{algorithm} @gol
 -fira-region=@var{region}  -fira-hoist-pressure @gol
 -fira-loop-pressure  -fno-ira-share-save-slots @gol
 -fno-ira-share-spill-slots @gol
@@ -8917,6 +8917,11 @@ Enabled by default at @option{-O} and higher.
 Discover read-only, write-only and non-addressable static variables.
 Enabled by default at @option{-O} and higher.
 
+@item -fipa-stack-alignment
+@opindex fipa-stack-alignment
+Reduce stack alignment on call sites if possible.
+Enabled by default.
+
 @item -fipa-pta
 @opindex fipa-pta
 Perform interprocedural pointer analysis and interprocedural modification

gcc/final.c

@@ -4890,7 +4890,8 @@ rest_of_clean_state (void)
   /* We can reduce stack alignment on call site only when we are sure that
      the function body just produced will be actually used in the final
      executable.  */
-  if (decl_binds_to_current_def_p (current_function_decl))
+  if (flag_ipa_stack_alignment
+      && decl_binds_to_current_def_p (current_function_decl))
     {
       unsigned int pref = crtl->preferred_stack_boundary;
       if (crtl->stack_alignment_needed > crtl->preferred_stack_boundary)

gcc/testsuite/ChangeLog

 2018-11-09  Martin Liska  <mliska@suse.cz>
 
+	* gcc.target/i386/ipa-stack-alignment.c: New test.
+
+2018-11-09  Martin Liska  <mliska@suse.cz>
+
 	* gcc.dg/tree-ssa/writeonly-2.c: New test.
 
 2018-11-09  Jakub Jelinek  <jakub@redhat.com>

gcc/testsuite/gcc.target/i386/ipa-stack-alignment.c

+/* { dg-do compile } */
+/* { dg-options "-fno-ipa-stack-alignment -O" } */
+
+typedef struct {
+  long a;
+  long b[];
+} c;
+
+c *d;
+void e() { d->b[0] = 5; }
+void f() { e(); }
+
+/* { dg-final { scan-assembler "sub.*%.sp" } } */