[RFA] Restore combine.c split point for multiply-accumulate instructions

[Jeff Law <law at redhat dot com>]

find_split_point will tend to favor splitting complex insns in such a 
way as to encourage multiply-add insns.  It does this by splitting an 
unrecognizable insn at the (plus (mult)).

Now that many MULTs are canonicalized as ASHIFT, that code to prefer the 
multiply-add is no longer triggering when it could/should.  This 
ultimately results in splitting at the ASHIFT rather than the containing 
PLUS and thus we generate distinct shift and add insns rather than a 
single shadd insn on the PA (and probably other architectures).

This patch will treat (plus (ashift)) just like (plus (mult)) which 
encourages creation of shift-add insns.

This has been bootstrapped and regression tested on 
x86-unknown-linux-gnu and with an hppa2.0w-hp-hpux11.00 cross compiler 
on the hppa.exp testsuite (full disclosure -- hppa.exp only has two 
tests, so it's far from extensive).

I've also verified this is one of the changes ultimately necessary to 
resolve the code generation regressions caused by Venkat's combine.c 
change on the PA across my 300+ testfiles for a PA cross compiler.

OK for the trunk?



Jeff



diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 490386e..250fa0a 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,8 @@
 2015-05-20  Jeff Law  <law@redhat.com>
 
+	* combine.c (find_split_point): Handle ASHIFT like MULT to encourage
+	multiply-accumulate/shift-add insn generation.
+
 	* config/pa/pa.c (pa_print_operand): New 'o' output modifier.
 	(pa_mem_shadd_constant_p): Renamed from pa_shadd_constant_p.
 	(pa_shadd_constant_p): Allow constants for shadd insns rather
diff --git a/gcc/combine.c b/gcc/combine.c
index a90849e..ab6de3a 100644
--- a/gcc/combine.c
+++ b/gcc/combine.c
@@ -5145,7 +5163,9 @@ find_split_point (rtx *loc, rtx_insn *insn, bool set_src)
       /* Split at a multiply-accumulate instruction.  However if this is
          the SET_SRC, we likely do not have such an instruction and it's
          worthless to try this split.  */
-      if (!set_src && GET_CODE (XEXP (x, 0)) == MULT)
+      if (!set_src
+	  && (GET_CODE (XEXP (x, 0)) == MULT
+	      || GET_CODE (XEXP (x, 0)) == ASHIFT))
         return loc;
 
     default:
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index f20a131..bac0973 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,5 +1,7 @@
 2015-05-20  Jeff Law  <law@redhat.com>
 
+	* gcc.target/hppa/shadd-2.c: New test.
+
 	* gcc.target/hppa/hppa.exp: New target test driver.
 	* gcc.target/hppa/shadd-1.c: New test.
 
diff --git a/gcc/testsuite/gcc.target/hppa/shadd-2.c b/gcc/testsuite/gcc.target/hppa/shadd-2.c
new file mode 100644
index 0000000..34708e5
--- /dev/null
+++ b/gcc/testsuite/gcc.target/hppa/shadd-2.c
@@ -0,0 +1,49 @@
+/* { dg-do compile }  */
+/* { dg-options "-O2" }  */
+/* { dg-final { scan-assembler-times "sh.add" 2 } }  */
+
+typedef struct rtx_def *rtx;
+typedef const struct rtx_def *const_rtx;
+enum machine_mode
+{
+  VOIDmode, BLKmode, CCmode, CCGCmode, CCGOCmode, CCNOmode, CCAmode, CCCmode,
+    CCOmode, CCSmode, CCZmode, CCFPmode, CCFPUmode, BImode, QImode, HImode,
+    SImode, DImode, TImode, OImode, QQmode, HQmode, SQmode, DQmode, TQmode,
+    UQQmode, UHQmode, USQmode, UDQmode, UTQmode, HAmode, SAmode, DAmode,
+    TAmode, UHAmode, USAmode, UDAmode, UTAmode, SFmode, DFmode, XFmode,
+    TFmode, SDmode, DDmode, TDmode, CQImode, CHImode, CSImode, CDImode,
+    CTImode, COImode, SCmode, DCmode, XCmode, TCmode, V2QImode, V4QImode,
+    V2HImode, V1SImode, V8QImode, V4HImode, V2SImode, V1DImode, V16QImode,
+    V8HImode, V4SImode, V2DImode, V1TImode, V32QImode, V16HImode, V8SImode,
+    V4DImode, V2TImode, V64QImode, V32HImode, V16SImode, V8DImode, V4TImode,
+    V2SFmode, V4SFmode, V2DFmode, V8SFmode, V4DFmode, V2TFmode, V16SFmode,
+    V8DFmode, V4TFmode, MAX_MACHINE_MODE, NUM_MACHINE_MODES = MAX_MACHINE_MODE
+};
+struct rtx_def
+{
+  __extension__ enum machine_mode mode:8;
+};
+struct target_regs
+{
+  unsigned char x_hard_regno_nregs[53][MAX_MACHINE_MODE];
+};
+extern void oof (void);
+extern int rhs_regno (rtx);
+
+extern struct target_regs default_target_regs;
+__inline__ unsigned int
+end_hard_regno (enum machine_mode mode, unsigned int regno)
+{
+  return regno +
+    ((&default_target_regs)->x_hard_regno_nregs)[regno][(int) mode];
+}
+
+void
+note_btr_set (rtx dest, const_rtx set
+	      __attribute__ ((__unused__)), void *data)
+{
+  int regno, end_regno;
+  end_regno = end_hard_regno (((dest)->mode), (rhs_regno (dest)));
+  for (; regno < end_regno; regno++)
+    oof ();
+}