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[COMMITTED,1/2] Phi analyzer - Do not create phi groups with a single phi.

Message ID 921b7149-303a-bf0f-e550-864d5d4b5056@redhat.com
State New
Headers show
Series [COMMITTED,1/2] Phi analyzer - Do not create phi groups with a single phi. | expand

Commit Message

Andrew MacLeod Aug. 23, 2023, 6:47 p.m. UTC 
Rangers Phi Analyzer was creating a group consisting of a single PHI, 
which was problematic.  It didn't really help anything, and it prevented 
larger groups from including those PHIs and stopped some useful things 
from happening.

Bootstrapped on x86_64-pc-linux-gnu  with no regressions. Pushed.

Andrew
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Patch

From 9855b3f0a2869d456f0ee34a94a1231eb6d44c4a Mon Sep 17 00:00:00 2001
From: Andrew MacLeod <amacleod@redhat.com>
Date: Wed, 16 Aug 2023 13:23:06 -0400
Subject: [PATCH 1/4] Don't process phi groups with one phi.

The phi analyzer should not create a phi group containing a single phi.

	* gimple-range-phi.cc (phi_analyzer::operator[]): Return NULL if
	no group was created.
	(phi_analyzer::process_phi): Do not create groups of one phi node.
---
 gcc/gimple-range-phi.cc | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/gcc/gimple-range-phi.cc b/gcc/gimple-range-phi.cc
index ffb4691d06b..a94b90a4660 100644
--- a/gcc/gimple-range-phi.cc
+++ b/gcc/gimple-range-phi.cc
@@ -344,9 +344,10 @@  phi_analyzer::operator[] (tree name)
       process_phi (as_a<gphi *> (SSA_NAME_DEF_STMT (name)));
       if (bitmap_bit_p (m_simple, v))
 	return  NULL;
-      // If m_simple bit isn't set, then process_phi allocated the table
-      // and should have a group.
-      gcc_checking_assert (v < m_tab.length ());
+     // If m_simple bit isn't set, and process_phi didn't allocated the table
+     // no group was created, so return NULL.
+     if (v >= m_tab.length ())
+      return NULL;
     }
   return m_tab[v];
 }
@@ -363,6 +364,7 @@  phi_analyzer::process_phi (gphi *phi)
   unsigned x;
   m_work.truncate (0);
   m_work.safe_push (gimple_phi_result (phi));
+  unsigned phi_count = 1;
   bitmap_clear (m_current);
 
   // We can only have 2 externals: an initial value and a modifier.
@@ -407,6 +409,7 @@  phi_analyzer::process_phi (gphi *phi)
 	      gimple *arg_stmt = SSA_NAME_DEF_STMT (arg);
 	      if (arg_stmt && is_a<gphi *> (arg_stmt))
 		{
+		  phi_count++;
 		  m_work.safe_push (arg);
 		  continue;
 		}
@@ -430,9 +433,12 @@  phi_analyzer::process_phi (gphi *phi)
 	}
     }
 
-  // If there are no names in the group, we're done.
-  if (bitmap_empty_p (m_current))
+  // If there are less than 2 names, just return.  This PHI may be included
+  // by another PHI, making it simple or a group of one will prevent a larger
+  // group from being formed.
+  if (phi_count < 2)
     return;
+  gcc_checking_assert (!bitmap_empty_p (m_current));
 
   phi_group *g = NULL;
   if (cycle_p)
-- 
2.41.0