Optimize display+display statements.

src/V3Const.cpp

@@ -1906,7 +1906,7 @@ private:
 	    }
 	    else if (0	// Disabled, as vpm assertions are faster without due to short-circuiting
 		     && operandIfIf(nodep)) {
-		UINFO(0,"IF({a}) IF({b}) => IF({a} && {b})"<<endl);
+		UINFO(9,"IF({a}) IF({b}) => IF({a} && {b})"<<endl);
 		AstNodeIf* lowerIfp = nodep->ifsp()->castNodeIf();
 		AstNode* condp = nodep->condp()->unlinkFrBack();
 		AstNode* lowerIfsp = lowerIfp->ifsp()->unlinkFrBackWithNext();
@@ -1922,6 +1922,49 @@ private:
 	}
     }
 
+    virtual void visit(AstDisplay* nodep) {
+        // DISPLAY(SFORMAT(text1)),DISPLAY(SFORMAT(text2)) -> DISPLAY(SFORMAT(text1+text2))
+        nodep->iterateChildren(*this);
+        if (stmtDisplayDisplay(nodep)) return;
+    }
+    bool stmtDisplayDisplay(AstDisplay* nodep) {
+        // DISPLAY(SFORMAT(text1)),DISPLAY(SFORMAT(text2)) -> DISPLAY(SFORMAT(text1+text2))
+        if (!m_modp) return false;  // Don't optimize under single statement
+        if (!nodep->backp()) return false;
+        AstDisplay* prevp = nodep->backp()->castDisplay();
+        if (!prevp) return false;
+        if (!((prevp->displayType() == nodep->displayType())
+              || (prevp->displayType() == AstDisplayType::DT_WRITE
+                  && nodep->displayType() == AstDisplayType::DT_DISPLAY)
+              || (prevp->displayType() == AstDisplayType::DT_DISPLAY
+                  && nodep->displayType() == AstDisplayType::DT_WRITE)))
+            return false;
+        if ((prevp->filep() && !nodep->filep())
+            || (!prevp->filep() && nodep->filep())
+            || !prevp->filep()->sameTree(nodep->filep())) return false;
+        if (!prevp->fmtp() || prevp->fmtp()->nextp()
+            || !nodep->fmtp() || nodep->fmtp()->nextp()) return false;
+        AstSFormatF* pformatp = prevp->fmtp();
+        if (!pformatp || pformatp->exprsp() || pformatp->scopeNamep()) return false;
+        AstSFormatF* nformatp = nodep->fmtp();
+        if (!nformatp || nformatp->exprsp() || nformatp->scopeNamep()) return false;
+        //
+        UINFO(9,"DISPLAY(SF({a})) DISPLAY(SF({b})) -> DISPLAY(SF({a}+{b}))"<<endl);
+        // Convert DT_DISPLAY to DT_WRITE as may allow later optimizations
+        if (prevp->displayType() == AstDisplayType::DT_DISPLAY) {
+            prevp->displayType(AstDisplayType::DT_WRITE);
+            pformatp->text(pformatp->text()+"\n");
+        }
+        // We can't replace prev() as the edit tracking iterators will get confused.
+        // So instead we edit the prev note itself.
+        if (prevp->addNewline()) pformatp->text(pformatp->text()+"\n");
+        pformatp->text(pformatp->text()+nformatp->text());
+        if (!prevp->addNewline() && nodep->addNewline()) {
+            pformatp->text(pformatp->text()+"\n");
+        }
+        nodep->unlinkFrBack()->deleteTree(); VL_DANGLING(nodep);
+        return true;
+    }
     virtual void visit(AstSFormatF* nodep) {
 	// Substitute constants into displays.  The main point of this is to
 	// simplify assertion methodologies which call functions with display's.
@@ -1960,7 +2003,7 @@ private:
 				UINFO(9,"     DispConst: "<<fmt<<" -> "<<out<<"  for "<<argp<<endl);
 				// fmt = out w/ replace % with %% as it must be literal.
 				fmt = VString::quotePercent(out);
-				argp->unlinkFrBack()->deleteTree();
+				argp->unlinkFrBack()->deleteTree(); VL_DANGLING(argp);
 			    }
 			    argp=nextp;
 			}

src/V3Descope.cpp

@@ -166,7 +166,7 @@ private:
 		    }
 		}
 		// Not really any way the user could do this, and we'd need to come up with some return value
-		//newfuncp->addStmtsp(new AstDisplay (newfuncp->fileline(), AstDisplayType::DT_DISPLAY,
+		//newfuncp->addStmtsp(new AstDisplay (newfuncp->fileline(), AstDisplayType::DT_WARNING,
 		//				      string("%%Error: ")+name+"() called with bad scope", NULL));
 		//newfuncp->addStmtsp(new AstStop (newfuncp->fileline()));
 		if (debug()>=9) newfuncp->dumpTree(cout,"   newfunc: ");

test_regress/t/t_display_merge.pl

@@ -0,0 +1,27 @@
+#!/usr/bin/perl
+if (!$::Driver) { use FindBin; exec("$FindBin::Bin/bootstrap.pl", @ARGV, $0); die; }
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2003 by Wilson Snyder. This program is free software; you can
+# redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+
+compile (
+    verilator_flags2=>["--stats"],
+    );
+
+execute (
+    check_finished=>1,
+    expect=> (quotemeta(
+'Merge:
+This should merge
+*-* All Finished *-*')
+	      .'.*')
+    );
+
+file_grep ("$Self->{obj_dir}/$Self->{VM_PREFIX}__stats.txt",
+	   qr/Node count, DISPLAY \s+ 5 \s+ 1 \s+ 1 \s+ 1/);
+
+ok(1);
+1;

test_regress/t/t_display_merge.v

@@ -0,0 +1,15 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed into the Public Domain, for any use,
+// without warranty, 2017 by Wilson Snyder.
+
+module t (/*AUTOARG*/);
+   initial begin
+      $display("Merge:");
+      $write("This ");
+      $write("should ");
+      $display("merge");
+      $write("*-* All Finished *-*\n");
+      $finish;
+   end
+endmodule