[PATCH] Avoid creating useless debug temporaries

[Eric Botcazou <botcazou@adacore.com>]

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Hi,

insert_debug_temp_for_var_def has some strange code whereby it creates debug 
temporaries for SINGLE_RHS (RHS for gimple_assign_single_p) but not for other 
RHS in the same situation.  Removing it saves 25% of compilation time at -g -O 
for a pathological testcase I have.

Bootstrapped/regtested on x86-64/Linux, OK for the mainline?


2023-04-25  Eric Botcazou  <ebotcazou@adacore.com>

	* tree-ssa.cc (insert_debug_temp_for_var_def): Do not create
	superfluous debug temporaries for single GIMPLE assignments.

-- 
Eric Botcazou

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diff --git a/gcc/tree-ssa.cc b/gcc/tree-ssa.cc
index a5cad2d344e..4ca1f5f3104 100644
--- a/gcc/tree-ssa.cc
+++ b/gcc/tree-ssa.cc
@@ -412,8 +412,7 @@ insert_debug_temp_for_var_def (gimple_stmt_iterator *gsi, tree var)
     {
       /* If there's a single use of VAR, and VAR is the entire debug
 	 expression (usecount would have been incremented again
-	 otherwise), and the definition involves only constants and
-	 SSA names, then we can propagate VALUE into this single use,
+	 otherwise), then we can propagate VALUE into this single use,
 	 avoiding the temp.
 
 	 We can also avoid using a temp if VALUE can be shared and
@@ -424,11 +423,9 @@ insert_debug_temp_for_var_def (gimple_stmt_iterator *gsi, tree var)
 	 are deferred to a debug temp, although we could avoid temps
 	 at the expense of duplication of expressions.  */
 
-      if (CONSTANT_CLASS_P (value)
+      if (usecount == 1
 	  || gimple_code (def_stmt) == GIMPLE_PHI
-	  || (usecount == 1
-	      && (!gimple_assign_single_p (def_stmt)
-		  || is_gimple_min_invariant (value)))
+	  || CONSTANT_CLASS_P (value)
 	  || is_gimple_reg (value))
 	;
       else
@@ -466,11 +463,6 @@ insert_debug_temp_for_var_def (gimple_stmt_iterator *gsi, tree var)
       if (value)
 	{
 	  FOR_EACH_IMM_USE_ON_STMT (use_p, imm_iter)
-	    /* unshare_expr is not needed here.  vexpr is either a
-	       SINGLE_RHS, that can be safely shared, some other RHS
-	       that was unshared when we found it had a single debug
-	       use, or a DEBUG_EXPR_DECL, that can be safely
-	       shared.  */
 	    SET_USE (use_p, unshare_expr (value));
 	  /* If we didn't replace uses with a debug decl fold the
 	     resulting expression.  Otherwise we end up with invalid IL.  */