Re: [PING^2][PATCH] -fuse-caller-save - Implement TARGET_FN_OTHER_HARD_REG_USAGE hook for MIPS

[Tom de Vries <Tom_deVries at mentor dot com>]

On 10-01-14 09:47, Richard Sandiford wrote:
> Tom de Vries <Tom_deVries@mentor.com> writes:
> > >   Why not just collect the usage information at
> > > the end of final rather than at the beginning, so that all splits during
> > > final have been done?
> >
> > If we have a call to a leaf function, the final rtl representation does not
> > contain calls. The problem does not lie in the final pass where the callee is
> > analyzed, but in the caller, where information is used, and where the unsplit
> > call is missing the clobber of r6.
>
> Ah, so when you're using this hook in final, you're actually adding in
> the set of registers that will be clobbered by a future caller's CALL_INSN,
> as well as the registers that are clobbered by the callee itself?

Right. The first part is not the intended usage of the hook, but it was the 
simplest fix.

> That seems a bit error-prone, since we don't know at this stage what
> the future caller will look like.  (Things like the target attribute
> make this harder to predict.)
>
> I think it would be cleaner to just calculate the callee-clobbered
> registers during final and leave the caller to say what it clobbers.

Agree. I've rewritten the patch as such.

> FWIW, I still think it'd be better to collect the set at the end of final
> (after any final splits) rather than at the beginning.

Hmm. I was not aware that splits can happen during final. I'll try to update 
that patch as well.

> > > For other cases (where the usage isn't explicit
> > > at the rtl level), why not record the usage in CALL_INSN_FUNCTION_USAGE
> > > instead?
> >
> > Right, we could add the r6 clobber that way. But to keep things simple, I've
> > used the hook instead.
>
> Why's it simpler though?  That's the kind of thing CALL_INSN_FUNCTION_USAGE
> is there for.

It was simpler to implement. But you're right, using CALL_INSN_FUNCTION_USAGE 
was simple as well.

build and reg-tested on MIPS. OK for stage1? (You've alread OK-ed the test-case 
part).

Thanks,
- Tom

> Thanks,
> Richard

2014-01-12  Radovan Obradovic  <robradovic@mips.com>
            Tom de Vries  <tom@codesourcery.com>

	* config/mips/mips.c (POST_CALL_TMP_REG): Define.
	(mips_split_call): Use POST_CALL_TMP_REG.
	(mips_fn_other_hard_reg_usage): New function.
	(TARGET_FN_OTHER_HARD_REG_USAGE): Define targhook using new function.
	(mips_expand_call): Add POST_CALL_TMP_REG clobber.

	* gcc.target/mips/mips.exp: Add use-caller-save to -ffoo/-fno-foo
	options.
	* gcc.target/mips/fuse-caller-save.c: New test.
---
 gcc/config/mips/mips.c                           | 41 +++++++++++++++++++++---
 gcc/testsuite/gcc.target/mips/fuse-caller-save.c | 30 +++++++++++++++++
 gcc/testsuite/gcc.target/mips/mips.exp           |  1 +
 3 files changed, 67 insertions(+), 5 deletions(-)
 create mode 100644 gcc/testsuite/gcc.target/mips/fuse-caller-save.c

diff --git a/gcc/config/mips/mips.c b/gcc/config/mips/mips.c
index 617391c..ef7a3f9 100644
--- a/gcc/config/mips/mips.c
+++ b/gcc/config/mips/mips.c
@@ -175,6 +175,11 @@ along with GCC; see the file COPYING3.  If not see
 /* Return the usual opcode for a nop.  */
 #define MIPS_NOP 0
 
+/* Temporary register that is used after a call, and suitable for both
+   MIPS16 and non-MIPS16 code.  $4 and $5 are used for returning complex double
+   values in soft-float code, so $6 is the first suitable candidate.  */
+#define POST_CALL_TMP_REG (GP_ARG_FIRST + 2)
+
 /* Classifies an address.
 
    ADDRESS_REG
@@ -6906,11 +6911,19 @@ mips_expand_call (enum mips_call_type type, rtx result, rtx addr,
 {
   rtx orig_addr, pattern, insn;
   int fp_code;
+  rtx post_call_tmp_reg = gen_rtx_REG (word_mode, POST_CALL_TMP_REG);
 
   fp_code = aux == 0 ? 0 : (int) GET_MODE (aux);
   insn = mips16_build_call_stub (result, &addr, args_size, fp_code);
   if (insn)
     {
+      if (TARGET_EXPLICIT_RELOCS
+	  && TARGET_CALL_CLOBBERED_GP
+	  && !find_reg_note (insn, REG_NORETURN, 0))
+	CALL_INSN_FUNCTION_USAGE (insn)
+	  = gen_rtx_EXPR_LIST (VOIDmode,
+			       gen_rtx_CLOBBER (VOIDmode, post_call_tmp_reg),
+			       CALL_INSN_FUNCTION_USAGE (insn));
       gcc_assert (!lazy_p && type == MIPS_CALL_NORMAL);
       return insn;
     }
@@ -6966,7 +6979,16 @@ mips_expand_call (enum mips_call_type type, rtx result, rtx addr,
       pattern = fn (result, addr, args_size);
     }
 
-  return mips_emit_call_insn (pattern, orig_addr, addr, lazy_p);
+  insn = mips_emit_call_insn (pattern, orig_addr, addr, lazy_p);
+  if (TARGET_EXPLICIT_RELOCS
+      && TARGET_CALL_CLOBBERED_GP
+      && !find_reg_note (insn, REG_NORETURN, 0))
+    CALL_INSN_FUNCTION_USAGE (insn)
+      = gen_rtx_EXPR_LIST (VOIDmode,
+			   gen_rtx_CLOBBER (VOIDmode, post_call_tmp_reg),
+			   CALL_INSN_FUNCTION_USAGE (insn));
+
+  return insn;
 }
 
 /* Split call instruction INSN into a $gp-clobbering call and
@@ -6978,10 +7000,8 @@ mips_split_call (rtx insn, rtx call_pattern)
 {
   emit_call_insn (call_pattern);
   if (!find_reg_note (insn, REG_NORETURN, 0))
-    /* Pick a temporary register that is suitable for both MIPS16 and
-       non-MIPS16 code.  $4 and $5 are used for returning complex double
-       values in soft-float code, so $6 is the first suitable candidate.  */
-    mips_restore_gp_from_cprestore_slot (gen_rtx_REG (Pmode, GP_ARG_FIRST + 2));
+    mips_restore_gp_from_cprestore_slot (gen_rtx_REG (Pmode,
+						      POST_CALL_TMP_REG));
 }
 
 /* Return true if a call to DECL may need to use JALX.  */
@@ -18687,6 +18707,14 @@ mips_case_values_threshold (void)
   else
     return default_case_values_threshold ();
 }
+
+/* Implement TARGET_FN_OTHER_HARD_REG_USAGE.  */
+
+static bool
+mips_fn_other_hard_reg_usage (struct hard_reg_set_container *fn_used_regs)
+{
+  return true;
+}
 
 /* Initialize the GCC target structure.  */
 #undef TARGET_ASM_ALIGNED_HI_OP
@@ -18921,6 +18949,9 @@ mips_case_values_threshold (void)
 #undef TARGET_CASE_VALUES_THRESHOLD
 #define TARGET_CASE_VALUES_THRESHOLD mips_case_values_threshold
 
+#undef TARGET_FN_OTHER_HARD_REG_USAGE
+#define TARGET_FN_OTHER_HARD_REG_USAGE mips_fn_other_hard_reg_usage
+
 struct gcc_target targetm = TARGET_INITIALIZER;
 
 #include "gt-mips.h"
diff --git a/gcc/testsuite/gcc.target/mips/fuse-caller-save.c b/gcc/testsuite/gcc.target/mips/fuse-caller-save.c
new file mode 100644
index 0000000..1fd6c7d
--- /dev/null
+++ b/gcc/testsuite/gcc.target/mips/fuse-caller-save.c
@@ -0,0 +1,30 @@
+/* { dg-do compile } */
+/* { dg-options "-fuse-caller-save" } */
+/* { dg-skip-if "" { *-*-* }  { "*" } { "-Os" } } */
+/* Testing -fuse-caller-save optimization option.  */
+
+static int __attribute__((noinline)) NOCOMPRESSION
+bar (int x)
+{
+  return x + 3;
+}
+
+int __attribute__((noinline)) NOCOMPRESSION
+foo (int y)
+{
+  return y + bar (y);
+}
+
+int NOCOMPRESSION
+main (void)
+{
+  return !(foo (5) == 13);
+}
+
+/* Check that there are only 2 stack-saves: r31 in main and foo.  */
+
+/* Check that there only 2 sw/sd.  */
+/* { dg-final { scan-assembler-times "(?n)s\[wd\]\t\\\$.*,.*\\(\\\$sp\\)" 2 } } */
+
+/* Check that the first caller-save register is unused.  */
+/* { dg-final { scan-assembler-not "\\\$16" } } */
diff --git a/gcc/testsuite/gcc.target/mips/mips.exp b/gcc/testsuite/gcc.target/mips/mips.exp
index 8c72cff..6ad8160 100644
--- a/gcc/testsuite/gcc.target/mips/mips.exp
+++ b/gcc/testsuite/gcc.target/mips/mips.exp
@@ -305,6 +305,7 @@ foreach option {
     tree-vectorize
     unroll-all-loops
     unroll-loops
+    use-caller-save
 } {
     lappend mips_option_groups $option "-f(no-|)$option"
 }
-- 
1.8.3.2