When a callchain entry has no srcline available, we ended up
comparing the instruction pointer. I consider this to be not
too useful. Rather, I think we should group the entries by
function name, which this patch adds. For people who want to
split the data on the IP boundary, using `-g address` is the
correct choice.

Before:

~~~~~
   100.00%    38.86%  [.] main
            |
            |--61.14%--main inlining.cpp:14
            |          std::norm<double> complex:664
            |          std::_Norm_helper<true>::_S_do_it<double> complex:654
            |          std::abs<double> complex:597
            |          std::__complex_abs complex:589
            |          |
            |          |--56.03%--hypot
            |          |          |
            |          |          |--8.45%--__hypot_finite
            |          |          |
            |          |          |--7.62%--__hypot_finite
            |          |          |
            |          |          |--2.29%--__hypot_finite
            |          |          |
            |          |          |--2.24%--__hypot_finite
            |          |          |
            |          |          |--2.06%--__hypot_finite
            |          |          |
            |          |          |--1.81%--__hypot_finite
...
~~~~~

After:

~~~~~
   100.00%    38.86%  [.] main
            |
            |--61.14%--main inlining.cpp:14
            |          std::norm<double> complex:664
            |          std::_Norm_helper<true>::_S_do_it<double> complex:654
            |          std::abs<double> complex:597
            |          std::__complex_abs complex:589
            |          |
            |          |--60.29%--hypot
            |          |          |
            |          |           --56.03%--__hypot_finite
            |          |
            |           --0.85%--cabs
~~~~~

Cc: Arnaldo Carvalho de Melo <redacted>
Cc: David Ahern <redacted>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <redacted>
Cc: Yao Jin <redacted>
Signed-off-by: Milian Wolff <redacted>
---
 tools/perf/util/callchain.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/tools/perf/util/callchain.c b/tools/perf/util/callchain.c
index d1c5d1d422cb..daf491ea0a7f 100644
--- a/tools/perf/util/callchain.c
+++ b/tools/perf/util/callchain.c

@@ -638,11 +638,9 @@ enum match_result {
 	MATCH_GT,
 };
 
-static enum match_result match_chain_srcline(struct callchain_cursor_node *node,
-					     struct callchain_list *cnode)
+static enum match_result match_chain_strings(const char *left,
+					     const char *right)
 {
-	const char *left = cnode->srcline;
-	const char *right = node->srcline;
 	enum match_result ret = MATCH_EQ;
 	int cmp;
 

@@ -652,10 +650,8 @@ static enum match_result match_chain_srcline(struct callchain_cursor_node *node,
 		cmp = 1;
 	else if (left && !right)
 		cmp = -1;
-	else if (cnode->ip == node->ip)
-		cmp = 0;
 	else
-		cmp = (cnode->ip < node->ip) ? -1 : 1;
+		return MATCH_ERROR;
 
 	if (cmp != 0)
 		ret = cmp < 0 ? MATCH_LT : MATCH_GT;

@@ -670,10 +666,18 @@ static enum match_result match_chain(struct callchain_cursor_node *node,
 	u64 left, right;
 
 	if (callchain_param.key == CCKEY_SRCLINE) {
-		enum match_result match = match_chain_srcline(node, cnode);
+		enum match_result match = match_chain_strings(cnode->srcline,
+							      node->srcline);
+
+		// if no srcline is available, fallback to symbol name
+		if (match == MATCH_ERROR && cnode->ms.sym && node->sym)
+			match = match_chain_strings(cnode->ms.sym->name,
+						    node->sym->name);
 
 		if (match != MATCH_ERROR)
 			return match;
+
+		// otherwise fall-back to IP-based comparison below
 	}
 
 	if (cnode->ms.sym && sym && callchain_param.key == CCKEY_FUNCTION) {

-- 
2.14.1