[PATCH, rs6000] Stop non-volatile CR usage from killing shrink-wrap

[Pat Haugen <pthaugen@linux.vnet.ibm.com>]

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The following patch allows shrink-wrapping to succeed in the presence of
non-volatile CR save/restore. The movesi_from_cr define_insn used to
list all CRs as used, even though it's only the non-volatile values that
we are interested in saving/restoring. This prevented the prolog from
being moved past the early exit test because that compare was defining a
register used in the prolog (a volatile CR). The patch removes the
mentions of the volatile CRs and renames the functions involved so that
it's hopefully clear they are for prolog generation only.

Bootstrap/regtest on powerpc64le-linux with no new regressions. Ok for
trunk?

-Pat



2017-08-28  Pat Haugen  <pthaugen@us.ibm.com>

	* config/rs6000/rs6000.c (rs6000_emit_prolog_move_from_cr): Rename from
	rs6000_emit_move_from_cr and call renamed function.
	(rs6000_emit_prologue): Call renamed functions.
	* config/rs6000/rs6000.md (prolog_movesi_from_cr): Rename from
	prolog_movesi_from_cr, remove volatile CRs.


testsuite/ChangeLog:
2017-08-28  Pat Haugen  <pthaugen@us.ibm.com>

	* gcc.target/powerpc/cr_shrink-wrap.c: New.


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Index: gcc/config/rs6000/rs6000.c
===================================================================
--- gcc/config/rs6000/rs6000.c	(revision 251389)
+++ gcc/config/rs6000/rs6000.c	(working copy)
@@ -26083,10 +26083,14 @@ rs6000_emit_savres_rtx (rs6000_stack_t *
   return insn;
 }
 
-/* Emit code to store CR fields that need to be saved into REG.  */
+/* Emit prolog code to store CR fields that need to be saved into REG. This
+   function should only be called when moving the non-volatile CRs to REG, it
+   is not a general purpose routine to move the entire set of CRs to REG.
+   Specifically, gen_prolog_movesi_from_cr() does not contain uses of the
+   volatile CRs.  */
 
 static void
-rs6000_emit_move_from_cr (rtx reg)
+rs6000_emit_prolog_move_from_cr (rtx reg)
 {
   /* Only the ELFv2 ABI allows storing only selected fields.  */
   if (DEFAULT_ABI == ABI_ELFv2 && TARGET_MFCRF)
@@ -26117,7 +26121,7 @@ rs6000_emit_move_from_cr (rtx reg)
 	 as well, using logical operations to combine the values.  */
     }
 
-  emit_insn (gen_movesi_from_cr (reg));
+  emit_insn (gen_prolog_movesi_from_cr (reg));
 }
 
 /* Return whether the split-stack arg pointer (r12) is used.  */
@@ -26857,7 +26861,7 @@ rs6000_emit_prologue (void)
     {
       cr_save_rtx = gen_rtx_REG (SImode, cr_save_regno);
       START_USE (cr_save_regno);
-      rs6000_emit_move_from_cr (cr_save_rtx);
+      rs6000_emit_prolog_move_from_cr (cr_save_rtx);
     }
 
   /* Do any required saving of fpr's.  If only one or two to save, do
@@ -27095,7 +27099,7 @@ rs6000_emit_prologue (void)
 	{
 	  START_USE (0);
 	  cr_save_rtx = gen_rtx_REG (SImode, 0);
-	  rs6000_emit_move_from_cr (cr_save_rtx);
+	  rs6000_emit_prolog_move_from_cr (cr_save_rtx);
 	}
 
       /* Saving CR requires a two-instruction sequence: one instruction
@@ -27182,7 +27186,7 @@ rs6000_emit_prologue (void)
       /* ??? We might get better performance by using multiple mfocrf
 	 instructions.  */
       crsave = gen_rtx_REG (SImode, 0);
-      emit_insn (gen_movesi_from_cr (crsave));
+      emit_insn (gen_prolog_movesi_from_cr (crsave));
 
       for (i = 0; i < 8; i++)
 	if (!call_used_regs[CR0_REGNO + i])
Index: gcc/config/rs6000/rs6000.md
===================================================================
--- gcc/config/rs6000/rs6000.md	(revision 251389)
+++ gcc/config/rs6000/rs6000.md	(working copy)
@@ -13032,12 +13032,14 @@ (define_insn "*movesi_from_cr_one"
 }"
   [(set_attr "type" "mfcrf")])
 
-(define_insn "movesi_from_cr"
+;; Don't include the volatile CRs since their values are not used wrt CR save
+;; in the prolog and doing so prevents shrink-wrapping because we can't move the
+;; prolog past an insn (early exit test) that defines a register used in the
+;; prolog.
+(define_insn "prolog_movesi_from_cr"
   [(set (match_operand:SI 0 "gpc_reg_operand" "=r")
-        (unspec:SI [(reg:CC CR0_REGNO) (reg:CC CR1_REGNO)
-		    (reg:CC CR2_REGNO) (reg:CC CR3_REGNO)
-		    (reg:CC CR4_REGNO) (reg:CC CR5_REGNO)
-		    (reg:CC CR6_REGNO) (reg:CC CR7_REGNO)]
+        (unspec:SI [(reg:CC CR2_REGNO) (reg:CC CR3_REGNO)
+		    (reg:CC CR4_REGNO)]
 		   UNSPEC_MOVESI_FROM_CR))]
   ""
   "mfcr %0"
Index: gcc/testsuite/gcc.target/powerpc/cr_shrink-wrap.c
===================================================================
--- gcc/testsuite/gcc.target/powerpc/cr_shrink-wrap.c	(nonexistent)
+++ gcc/testsuite/gcc.target/powerpc/cr_shrink-wrap.c	(working copy)
@@ -0,0 +1,11 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-rtl-pro_and_epilogue" } */
+
+void foo(int i)
+{
+  if (i > 0)
+    /* Non-volatile CR kill on true path should not prevent shrink-wrap.  */
+    asm ("" : : : "cr2", "cr3");
+}
+
+/* { dg-final { scan-rtl-dump-times "Performing shrink-wrapping" 1 "pro_and_epilogue" } } */