[PATCH] D84802: Add control over debug lines dropping

[Jacek Galazka via Phabricator via llvm-commits]

jacek-galazka created this revision.
jacek-galazka added a reviewer: echristo.
Herald added subscribers: llvm-commits, asbirlea, hiraditya.
Herald added a project: LLVM.
jacek-galazka requested review of this revision.

Control if GVN and LICM pass should retain debug locations of moved instructions.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D84802

Files:
  llvm/lib/Transforms/Scalar/GVN.cpp
  llvm/lib/Transforms/Scalar/LICM.cpp


Index: llvm/lib/Transforms/Scalar/LICM.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/LICM.cpp
+++ llvm/lib/Transforms/Scalar/LICM.cpp
@@ -134,6 +134,10 @@
              "number of accesses allowed to be present in a loop in order to "
              "enable memory promotion."));
 
+cl::opt<bool> AllowJumpyDebugTables(
+    "allow-jumpy-debug-lines-tables", cl::Hidden, cl::init(false),
+    cl::desc("Retain debug locations of instructions moved by eg. LICM."));
+
 static bool inSubLoop(BasicBlock *BB, Loop *CurLoop, LoopInfo *LI);
 static bool isNotUsedOrFreeInLoop(const Instruction &I, const Loop *CurLoop,
                                   const LoopSafetyInfo *SafetyInfo,
@@ -1659,9 +1663,10 @@
     moveInstructionBefore(I, *Dest->getTerminator(), *SafetyInfo, MSSAU, SE);
 
   // Apply line 0 debug locations when we are moving instructions to different
-  // basic blocks because we want to avoid jumpy line tables.
+  // basic blocks if we want to avoid jumpy line tables.
   if (const DebugLoc &DL = I.getDebugLoc())
-    I.setDebugLoc(DebugLoc::get(0, 0, DL.getScope(), DL.getInlinedAt()));
+    if (!AllowJumpyDebugTables)
+      I.setDebugLoc(DebugLoc::get(0, 0, DL.getScope(), DL.getInlinedAt()));
 
   if (isa<LoadInst>(I))
     ++NumMovedLoads;
Index: llvm/lib/Transforms/Scalar/GVN.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/GVN.cpp
+++ llvm/lib/Transforms/Scalar/GVN.cpp
@@ -122,6 +122,8 @@
              "into) when deducing if a value is fully avaliable or not in GVN "
              "(default = 600)"));
 
+extern cl::opt<bool> AllowJumpyDebugTables;
+
 struct llvm::GVN::Expression {
   uint32_t opcode;
   bool commutative = false;
@@ -1312,10 +1314,12 @@
   // Assign value numbers to the new instructions.
   for (Instruction *I : NewInsts) {
     // Instructions that have been inserted in predecessor(s) to materialize
-    // the load address do not retain their original debug locations. Doing
-    // so could lead to confusing (but correct) source attributions.
+    // the load address can retain their original debug locations. Doing
+    // so leads to confusing source attributions. However as locations are
+    // correct, they can be useful.
     if (const DebugLoc &DL = I->getDebugLoc())
-      I->setDebugLoc(DebugLoc::get(0, 0, DL.getScope(), DL.getInlinedAt()));
+      if (!AllowJumpyDebugTables)
+        I->setDebugLoc(DebugLoc::get(0, 0, DL.getScope(), DL.getInlinedAt()));
 
     // FIXME: We really _ought_ to insert these value numbers into their
     // parent's availability map.  However, in doing so, we risk getting into


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