[PATCH] Take register pressure into account for vec_construct/scalar_to_vec when the components are not loaded from memory.

[liuhongt <hongtao.liu@intel.com>]

> Hmm, I would suggest you put reg_needed into the class and accumulate
> over all vec_construct, with your patch you pessimize a single v32qi
> over two separate v16qi for example.  Also currently the whole block is
> gated with INTEGRAL_TYPE_P but register pressure would be also
> a concern for floating point vectors.  finish_cost would then apply an
> adjustment.

Changed.

> 'target_avail_regs' is for GENERAL_REGS, does that include APX regs?
> I don't see anything similar for FP regs, but I guess the target should know
> or maybe there's a #regs in regclass query already.
Haven't see any, use below setting.

unsigned target_avail_sse = TARGET_64BIT ? (TARGET_AVX512F ? 32 : 16) : 8;

Bootstrapped and regtested on x86_64-pc-linux-gnu{-m32,}.
No big impact on SPEC2017.
Observe 1 big improvement from other benchmark by avoiding vectorization with
vec_construct v32qi which caused lots of spills.

Ok for trunk?

For vec_contruct, the components must be live at the same time if
they're not loaded from memory, when the number of those components
exceeds available registers, spill happens. Try to account that with a
rough estimation.
??? Ideally, we should have an overall estimation of register pressure
if we know the live range of all variables.

gcc/ChangeLog:

	* config/i386/i386.cc (ix86_vector_costs::add_stmt_cost):
	Count sse_reg/gpr_regs for components not loaded from memory.
	(ix86_vector_costs:ix86_vector_costs): New constructor.
	(ix86_vector_costs::m_num_gpr_needed[3]): New private memeber.
	(ix86_vector_costs::m_num_sse_needed[3]): Ditto.
	(ix86_vector_costs::finish_cost): Estimate overall register
	pressure cost.
	(ix86_vector_costs::ix86_vect_estimate_reg_pressure): New
	function.
---
 gcc/config/i386/i386.cc | 54 ++++++++++++++++++++++++++++++++++++++---
 1 file changed, 50 insertions(+), 4 deletions(-)

diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
index 9390f525b99..dcaea6c2096 100644
--- a/gcc/config/i386/i386.cc
+++ b/gcc/config/i386/i386.cc
@@ -24562,15 +24562,34 @@ ix86_noce_conversion_profitable_p (rtx_insn *seq, struct noce_if_info *if_info)
 /* x86-specific vector costs.  */
 class ix86_vector_costs : public vector_costs
 {
-  using vector_costs::vector_costs;
+public:
+  ix86_vector_costs (vec_info *, bool);
 
   unsigned int add_stmt_cost (int count, vect_cost_for_stmt kind,
 			      stmt_vec_info stmt_info, slp_tree node,
 			      tree vectype, int misalign,
 			      vect_cost_model_location where) override;
   void finish_cost (const vector_costs *) override;
+
+private:
+
+  /* Estimate register pressure of the vectorized code.  */
+  void ix86_vect_estimate_reg_pressure ();
+  /* Number of GENERAL_REGS/SSE_REGS used in the vectorizer, it's used for
+     estimation of register pressure.
+     ??? Currently it's only used by vec_construct/scalar_to_vec
+     where we know it's not loaded from memory.  */
+  unsigned m_num_gpr_needed[3];
+  unsigned m_num_sse_needed[3];
 };
 
+ix86_vector_costs::ix86_vector_costs (vec_info* vinfo, bool costing_for_scalar)
+  : vector_costs (vinfo, costing_for_scalar),
+    m_num_gpr_needed (),
+    m_num_sse_needed ()
+{
+}
+
 /* Implement targetm.vectorize.create_costs.  */
 
 static vector_costs *
@@ -24748,8 +24767,7 @@ ix86_vector_costs::add_stmt_cost (int count, vect_cost_for_stmt kind,
     }
   else if ((kind == vec_construct || kind == scalar_to_vec)
 	   && node
-	   && SLP_TREE_DEF_TYPE (node) == vect_external_def
-	   && INTEGRAL_TYPE_P (TREE_TYPE (vectype)))
+	   && SLP_TREE_DEF_TYPE (node) == vect_external_def)
     {
       stmt_cost = ix86_builtin_vectorization_cost (kind, vectype, misalign);
       unsigned i;
@@ -24785,7 +24803,15 @@ ix86_vector_costs::add_stmt_cost (int count, vect_cost_for_stmt kind,
 		  && (gimple_assign_rhs_code (def) != BIT_FIELD_REF
 		      || !VECTOR_TYPE_P (TREE_TYPE
 				(TREE_OPERAND (gimple_assign_rhs1 (def), 0))))))
-	    stmt_cost += ix86_cost->sse_to_integer;
+	    {
+	      if (fp)
+		m_num_sse_needed[where]++;
+	      else
+		{
+		  m_num_gpr_needed[where]++;
+		  stmt_cost += ix86_cost->sse_to_integer;
+		}
+	    }
 	}
       FOR_EACH_VEC_ELT (SLP_TREE_SCALAR_OPS (node), i, op)
 	if (TREE_CODE (op) == SSA_NAME)
@@ -24821,6 +24847,24 @@ ix86_vector_costs::add_stmt_cost (int count, vect_cost_for_stmt kind,
   return retval;
 }
 
+void
+ix86_vector_costs::ix86_vect_estimate_reg_pressure ()
+{
+  unsigned gpr_spill_cost = COSTS_N_INSNS (ix86_cost->int_store [2]) / 2;
+  unsigned sse_spill_cost = COSTS_N_INSNS (ix86_cost->sse_store[0]) / 2;
+
+  /* Any better way to have target available fp registers, currently use SSE_REGS.  */
+  unsigned target_avail_sse = TARGET_64BIT ? (TARGET_AVX512F ? 32 : 16) : 8;
+  for (unsigned i = 0; i != 3; i++)
+    {
+      if (m_num_gpr_needed[i] > target_avail_regs)
+	m_costs[i] += gpr_spill_cost * (m_num_gpr_needed[i] - target_avail_regs);
+      /* Only measure sse registers pressure.  */
+      if (TARGET_SSE && (m_num_sse_needed[i] > target_avail_sse))
+	m_costs[i] += sse_spill_cost * (m_num_sse_needed[i] - target_avail_sse);
+    }
+}
+
 void
 ix86_vector_costs::finish_cost (const vector_costs *scalar_costs)
 {
@@ -24843,6 +24887,8 @@ ix86_vector_costs::finish_cost (const vector_costs *scalar_costs)
 	m_costs[vect_body] = INT_MAX;
     }
 
+  ix86_vect_estimate_reg_pressure ();
+
   vector_costs::finish_cost (scalar_costs);
 }
 
-- 
2.31.1