From: David Malcolm <dmalcolm@redhat.com>
Date: Wed, 16 Sep 2020 17:12:39 +0000 (-0400)
Subject: analyzer: getchar has no side-effects
X-Git-Tag: basepoints/gcc-12~5015
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e097c9ab83192fc2f738ec6426a275282e9a51ea;p=thirdparty%2Fgcc.git

analyzer: getchar has no side-effects

Seen whilst debugging another issue, where the analyzer was assuming
conservatively that a call to getchar could clobber a global.

This is handled for most of the other stdio functions by the list
in sm-file.cc

gcc/analyzer/ChangeLog:
	* region-model.cc (region_model::on_call_pre): Treat getchar as
	having no side-effects.

gcc/testsuite/ChangeLog:
	* gcc.dg/analyzer/getchar-1.c: New test.
---

diff --git a/gcc/analyzer/region-model.cc b/gcc/analyzer/region-model.cc
index d53272e4332c..1312391557db 100644
--- a/gcc/analyzer/region-model.cc
+++ b/gcc/analyzer/region-model.cc
@@ -732,6 +732,11 @@ region_model::on_call_pre (const gcall *call, region_model_context *ctxt)
 	return impl_call_calloc (cd);
       else if (is_named_call_p (callee_fndecl, "alloca", call, 1))
 	return impl_call_alloca (cd);
+      else if (is_named_call_p (callee_fndecl, "getchar", call, 0))
+	{
+	  /* No side-effects (tracking stream state is out-of-scope
+	     for the analyzer).  */
+	}
       else if (is_named_call_p (callee_fndecl, "memset", call, 3))
 	{
 	  impl_call_memset (cd);
diff --git a/gcc/testsuite/gcc.dg/analyzer/getchar-1.c b/gcc/testsuite/gcc.dg/analyzer/getchar-1.c
new file mode 100644
index 000000000000..25595e0786ee
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/analyzer/getchar-1.c
@@ -0,0 +1,19 @@
+#include <stdio.h>
+#include "analyzer-decls.h"
+
+int test_1 (void)
+{
+  int c = getchar ();
+  return c;
+}
+
+int glob_2;
+int test_2 (void)
+{
+  int c;
+  glob_2 = 42;
+  __analyzer_eval (glob_2 == 42); /* { dg-warning "TRUE" } */
+  c = getchar ();
+  __analyzer_eval (glob_2 == 42); /* { dg-warning "TRUE" } */
+  return c;
+}