[DebugInfo][RemoveDIs] Don't pointlessly scan funcs for debug-info (#79327)

The utility functions this patch modifies are part of cleanly
transitioning from a context where we use dbg.value intrinsics to one
where we use DPValue objects to record debug-info, and back again.
However, this is a waste of time in non-debug builds (i.e. no -g on the
command line). We still have to call the function on all blocks though
to set the IsNewDbgInfoFormat flag.

To reduce the overhead of this, test whether there's any debug-info in
the function by checking whether the function has a DISubprogram, and
pass a flag down to the utility functions indicating whether they can
skip the scan.

It feels a bit dumb to me now that we're scanning and setting a flag in
a load of blocks when we don't have to -- however it's been really
valuable during development for working out where spurious dbg.value
intrinsics leak into a RemoveDIs context. Happily we'll be able to just
delete this flag entirely when RemoveDIs lands and sticks, and the
conversion routines will eventually be pushed down into the debug-info
autoupgrade path.

1 files changed, 10 insertions, 2 deletions

diff --git a/llvm/lib/IR/BasicBlock.cpp b/llvm/lib/IR/BasicBlock.cpp
index dca528328384..e9d15989b6e5 100644
--- a/llvm/lib/IR/BasicBlock.cpp
+++ b/llvm/lib/IR/BasicBlock.cpp
@@ -60,13 +60,17 @@ DPMarker *BasicBlock::createMarker(InstListType::iterator It) {
   return DPM;
 }
 
-void BasicBlock::convertToNewDbgValues() {
+void BasicBlock::convertToNewDbgValues(bool HasNoDebugInfo) {
   // Is the command line option set?
   if (!UseNewDbgInfoFormat)
     return;
 
   IsNewDbgInfoFormat = true;
 
+  // If the caller knows there's no debug-info in this function, do nothing.
+  if (HasNoDebugInfo)
+    return;
+
   // Iterate over all instructions in the instruction list, collecting dbg.value
   // instructions and converting them to DPValues. Once we find a "real"
   // instruction, attach all those DPValues to a DPMarker in that instruction.
@@ -93,10 +97,14 @@ void BasicBlock::convertToNewDbgValues() {
   }
 }
 
-void BasicBlock::convertFromNewDbgValues() {
+void BasicBlock::convertFromNewDbgValues(bool HasNoDebugInfo) {
   invalidateOrders();
   IsNewDbgInfoFormat = false;
 
+  // If the caller knows there's no debug-info in this function, do nothing.
+  if (HasNoDebugInfo)
+    return;
+
   // Iterate over the block, finding instructions annotated with DPMarkers.
   // Convert any attached DPValues to dbg.values and insert ahead of the
   // instruction.