From 70167935fc3299af0397c2269a990f15666a1bde Mon Sep 17 00:00:00 2001
From: William Cohen <wcohen@redhat.com>
Date: Wed, 22 Sep 2021 17:34:25 -0400
Subject: [PATCH] Do liveness analysis after location information set and use
 regno info

Initially the call to the liveness analysis was being done before
the location information was setup.  Relocated the call after the
location information has been setup.

Corrected liveness analysis code to use the register number.  Also
added print out the function the liveness analysis is being run on.
Note that for probes on inlined functions this name will be different
than the probe point function name, it will be the actual function
that the code was inlined into.
---
 analysis.cxx |  9 +++------
 tapsets.cxx  | 14 +++++++-------
 2 files changed, 10 insertions(+), 13 deletions(-)

diff --git a/analysis.cxx b/analysis.cxx
index 60962f245..2c0da978a 100644
--- a/analysis.cxx
+++ b/analysis.cxx
@@ -199,7 +199,6 @@ int liveness(const char *executable,
 	// Determine whether 32-bit or 64-bit code as the register names are different in dyninst
 	int reg_width = func_to_analyze.co->cs()->getAddressWidth();
 
-	#if 0
 	// Find where the variable is located
 	location *loc = ctx.locations.back ();
 
@@ -207,10 +206,7 @@ int liveness(const char *executable,
 	if (loc->type != loc_register) return 0;
 
 	// Map dwarf number to dyninst register name, punt if out of range
-	unsigned int regno = loc->offset;
-	#else
-	unsigned int regno = 5; // Dummy up to arg1 of x86
-	#endif
+	unsigned int regno = loc->regno;
 	switch (reg_width){
 	case 4:
 		if (regno >= (sizeof(dyninst_register_32)/sizeof(MachRegister))) return 0;
@@ -248,7 +244,8 @@ int liveness(const char *executable,
 	// Query to see if whether the register is live at that point
 	bool used;
 	la.query(iloc, LivenessAnalyzer::Before, r, used);
-	cout << "liveness analysis " << executable << " " << hex << addr << endl;
+	cout << "liveness analysis " << executable << " " << func->name()
+	     << " " << hex << addr << endl;
 	cout << r.name() <<  (used ? " used"  : " unused") << endl;
 	return (used ? 1 : -1);
 }
diff --git a/tapsets.cxx b/tapsets.cxx
index 348d9c613..f4876cc5f 100644
--- a/tapsets.cxx
+++ b/tapsets.cxx
@@ -4721,13 +4721,6 @@ dwarf_var_expanding_visitor::visit_target_symbol (target_symbol *e)
       ctx.pc = addr;
       ctx.userspace_p = userspace_p;
 
-      // Check if change to variable has any effect
-      if (lvalue) {
-	      if (liveness(q.dw.module_name.c_str(), addr, ctx) < 0) {
-		      // warn that the write has no effect
-	      }
-      }
-
       // NB: pass the ctx.e (copied/rewritten veraion e, not orig_e),
       // so [x] index expressions have their intra-synthetic-function names
       Dwarf_Die endtype;
@@ -4737,6 +4730,13 @@ dwarf_var_expanding_visitor::visit_target_symbol (target_symbol *e)
 	q.dw.literal_stmt_for_local (ctx, getscopes(e), e->sym_name(),
 				     ctx.e, lvalue, &endtype);
 
+      // Now that have location information check if change to variable has any effect
+      if (lvalue) {
+	      if (liveness(q.dw.module_name.c_str(), addr, ctx) < 0) {
+		      // FIXME: warn that the write has no effect
+	      }
+      }
+
       q.dw.sess.globals.insert(q.dw.sess.globals.end(),
                               ctx.globals.begin(),
                               ctx.globals.end());
-- 
2.43.5