Source map fixes (#6550)

* Keep debug locations at function start

The `fn_prolog_epilog.debugInfo` test is failing otherwise, since there
was debug information associated to the nop instruction at the beginning
of the function.

* Do not clear the debug information when reaching the end of the source map

The last segment should extend to the end of the function.

* Propagate debug location from the function prolog to its first instruction

* Fix printing of epilogue location

The text parser no longer propagates locations to the epilogue, so we
should always print the location if there is one.

* Fix debug location smearing

The debug location of the last instruction should not smear into the
function epilogue, and a debug location from a previous function should
not smear into the prologue of the current function.

2 files changed, 5 insertions, 2 deletions

diff --git a/src/passes/DebugLocationPropagation.cpp b/src/passes/DebugLocationPropagation.cpp
index 07ae53faa..e2d1ac50f 100644
--- a/src/passes/DebugLocationPropagation.cpp
+++ b/src/passes/DebugLocationPropagation.cpp
@@ -64,6 +64,10 @@ struct DebugLocationPropagation
         if (auto it = locs.find(previous); it != locs.end()) {
           locs[curr] = it->second;
         }
+      } else if (self->getFunction()->prologLocation.size()) {
+        // Instructions may inherit their locations from the function
+        // prolog.
+        locs[curr] = *self->getFunction()->prologLocation.begin();
       }
     }
     expressionStack.push_back(curr);
diff --git a/src/passes/Print.cpp b/src/passes/Print.cpp
index b30a1180d..1ecf382d9 100644
--- a/src/passes/Print.cpp
+++ b/src/passes/Print.cpp
@@ -3025,8 +3025,7 @@ void PrintSExpression::visitDefinedFunction(Function* curr) {
     // Print the stack IR.
     printStackIR(curr->stackIR.get(), *this);
   }
-  if (currFunction->epilogLocation.size() &&
-      lastPrintedLocation != *currFunction->epilogLocation.begin()) {
+  if (currFunction->epilogLocation.size()) {
     // Print last debug location: mix of decIndent and printDebugLocation
     // logic.
     doIndent(o, indent);