re PR rtl-optimization/68920 (Undesirable if-conversion for a rarely taken branch)

gcc/

2016-01-11  Yuri Rumyantsev  <ysrumyan@gmail.com>

	PR rtl-optimization/68920
	* config/i386/i386.c (ix86_option_override_internal): Restrict number
	of conditional moves for  RTL if-conversion to 1 for
	TARGET_ONE_IF_CONV_INSN.
	* config/i386/i386.h (TARGET_ONE_IF_CONV_INSN): New macros.
	* config/i386/x86-tune.def (X86_TUNE_ONE_IF_CONV_INSN): New macros.
	* params.def (PARAM_MAX_RTL_IF_CONVERSION_INSNS) : Introduce new
	parameter to restirct number of conditional moves for
	RTL if-conversion.
	* doc/invoke.texi (max-rtl-if-conversion-insns): Document it.
	* ifcvt.c (bb_ok_for_noce_convert_multiple_sets): Limit number of
	conditionl moves.

gcc/testsuite/

2016-01-11  Yuri Rumyantsev  <ysrumyan@gmail.com>

	PR rtl-optimization/68920
	* gcc.dg/ifcvt-4.c: Add "--param max-rtl-if-conversion-insns=3" option
	for ix86 targets.
	* gcc.dg/ifcvt-5.c: New test.

From-SVN: r232220

gcc/ChangeLog

+2016-01-11  Yuri Rumyantsev  <ysrumyan@gmail.com>
+
+	PR rtl-optimization/68920
+	* config/i386/i386.c (ix86_option_override_internal): Restrict number
+	of conditional moves for  RTL if-conversion to 1 for
+	TARGET_ONE_IF_CONV_INSN.
+	* config/i386/i386.h (TARGET_ONE_IF_CONV_INSN): New macros.
+	* config/i386/x86-tune.def (X86_TUNE_ONE_IF_CONV_INSN): New macros.
+	* params.def (PARAM_MAX_RTL_IF_CONVERSION_INSNS) : Introduce new
+	parameter to restirct number of conditional moves for
+	RTL if-conversion.
+	* doc/invoke.texi (max-rtl-if-conversion-insns): Document it.
+	* ifcvt.c (bb_ok_for_noce_convert_multiple_sets): Limit number of
+	conditionl moves.
+
 2016-01-11  Alexandre Oliva <aoliva@redhat.com>
 
 	PR bootstrap/69123

gcc/config/i386/i386.c

@@ -5343,6 +5343,13 @@ ix86_option_override_internal (bool main_args_p,
 			 opts->x_param_values,
 			 opts_set->x_param_values);
 
+  /* Restrict number of if-converted SET insns to 1.  */
+  if (TARGET_ONE_IF_CONV_INSN)
+    maybe_set_param_value (PARAM_MAX_RTL_IF_CONVERSION_INSNS,
+			   1,
+			   opts->x_param_values,
+			   opts_set->x_param_values);
+
   /* Enable sw prefetching at -O3 for CPUS that prefetching is helpful.  */
   if (opts->x_flag_prefetch_loop_arrays < 0
       && HAVE_prefetch

gcc/config/i386/i386.h

@@ -499,6 +499,8 @@ extern unsigned char ix86_tune_features[X86_TUNE_LAST];
     ix86_tune_features[X86_TUNE_ADJUST_UNROLL]
 #define TARGET_AVOID_FALSE_DEP_FOR_BMI \
 	ix86_tune_features[X86_TUNE_AVOID_FALSE_DEP_FOR_BMI]
+#define TARGET_ONE_IF_CONV_INSN \
+	ix86_tune_features[X86_TUNE_ONE_IF_CONV_INSN]
 
 /* Feature tests against the various architecture variations.  */
 enum ix86_arch_indices {

gcc/config/i386/x86-tune.def

@@ -550,3 +550,8 @@ DEF_TUNE (X86_TUNE_PROMOTE_QI_REGS, "promote_qi_regs", 0)
    unrolling small loop less important. For, such architectures we adjust
    the unroll factor so that the unrolled loop fits the loop buffer.  */
 DEF_TUNE (X86_TUNE_ADJUST_UNROLL, "adjust_unroll_factor", m_BDVER3 | m_BDVER4)
+
+/* X86_TUNE_ONE_IF_CONV_INSNS: Restrict a number of set insns to be
+   if-converted to one.  */
+DEF_TUNE (X86_TUNE_ONE_IF_CONV_INSN, "one_if_conv_insn",
+	  m_SILVERMONT | m_KNL | m_INTEL | m_CORE_ALL | m_GENERIC)

gcc/doc/invoke.texi

@@ -10365,6 +10365,14 @@ In each case, the @var{value} is an integer.  The allowable choices for
 When branch is predicted to be taken with probability lower than this threshold
 (in percent), then it is considered well predictable. The default is 10.
 
+@item max-rtl-if-conversion-insns
+RTL if-conversion tries to remove conditional branches around a block and
+replace them with conditionally executed instructions.  This parameter
+gives the maximum number of instructions in a block which should be
+considered for if-conversion.  The default is 10, though the compiler will
+also use other heuristics to decide whether if-conversion is likely to be
+profitable.
+
 @item max-crossjump-edges
 The maximum number of incoming edges to consider for cross-jumping.
 The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in

gcc/ifcvt.c

@@ -44,6 +44,7 @@
 #include "shrink-wrap.h"
 #include "rtl-iter.h"
 #include "ifcvt.h"
+#include "params.h"
 
 #ifndef MAX_CONDITIONAL_EXECUTE
 #define MAX_CONDITIONAL_EXECUTE \
@@ -3242,6 +3243,8 @@ bb_ok_for_noce_convert_multiple_sets (basic_block test_bb,
 {
   rtx_insn *insn;
   unsigned count = 0;
+  unsigned param = PARAM_VALUE (PARAM_MAX_RTL_IF_CONVERSION_INSNS);
+  unsigned limit = MIN (ii->branch_cost, param);
 
   FOR_BB_INSNS (test_bb, insn)
     {
@@ -3277,8 +3280,8 @@ bb_ok_for_noce_convert_multiple_sets (basic_block test_bb,
   /* FORNOW: Our cost model is a count of the number of instructions we
      would if-convert.  This is suboptimal, and should be improved as part
      of a wider rework of branch_cost.  */
-  if (count > ii->branch_cost)
-    return FALSE;
+  if (count > limit)
+    return false;
 
   return count > 0;
 }
@@ -3823,7 +3826,6 @@ cond_move_process_if_block (struct noce_if_info *if_info)
     }
 
   num_updated_if_blocks++;
-
   success_p = TRUE;
 
 done:
@@ -4810,7 +4812,6 @@ find_if_case_1 (basic_block test_bb, edge then_edge, edge else_edge)
 
   num_true_changes++;
   num_updated_if_blocks++;
-
   return TRUE;
 }
 

gcc/params.def

@@ -1177,6 +1177,12 @@ DEFPARAM (PARAM_MAX_SSA_NAME_QUERY_DEPTH,
 	  "Maximum recursion depth allowed when querying a property of an"
 	  " SSA name.",
 	  2, 1, 0)
+
+DEFPARAM (PARAM_MAX_RTL_IF_CONVERSION_INSNS,
+	  "max-rtl-if-conversion-insns",
+	  "Maximum number of insns in a basic block to consider for RTL "
+	  "if-conversion.",
+	  10, 0, 99)
 /*
 
 Local variables:

gcc/testsuite/ChangeLog

+2016-01-11  Yuri Rumyantsev  <ysrumyan@gmail.com>
+
+	PR rtl-optimization/68920
+	* gcc.dg/ifcvt-4.c: Add "--param max-rtl-if-conversion-insns=3" option
+	for ix86 targets.
+	* gcc.dg/ifcvt-5.c: New test.
+
 2016-01-11  Alexandre Oliva <aoliva@redhat.com>
 
 	PR bootstrap/69123

gcc/testsuite/gcc.dg/ifcvt-4.c

-/* { dg-options "-fdump-rtl-ce1 -O2" } */
+/* { dg-options "-fdump-rtl-ce1 -O2 --param max-rtl-if-conversion-insns=3" } */
 /* { dg-skip-if "Multiple set if-conversion not guaranteed on all subtargets" { "arm*-*-* powerpc64le*-*-*" } {"*"} { "" } }  */
 
 int

gcc/testsuite/gcc.dg/ifcvt-5.c

+/* Check that multi-insn if-conversion is not done if the override
+   parameter would not allow it.  */
+
+/* { dg-options "-fdump-rtl-ce1 -O2 --param max-rtl-if-conversion-insns=1" } */
+int
+foo (int x, int y, int a)
+{
+  int i = x;
+  int j = y;
+  if (x > y)
+    {
+      i = a;
+      j = i;
+    }
+  return i * j;
+}
+/* { dg-final { scan-rtl-dump "0 true changes made" "ce1" } } */