[GlobalISel][IRTranslator] Add debug loc with line 0 to constants emitted into the entry block.

Constants, including G_GLOBAL_VALUE, are all emitted into the entry block which
lets us use the vreg def assuming it dominates all other users. However, it can
cause jumpy debug behaviour since the DebugLoc attached to these MIs are from
a user instruction that could be in a different block.

Fixes PR40887.

Differential Revision: https://reviews.llvm.org/D63286

llvm-svn: 363331

1 files changed, 14 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp b/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
index 78b452899ef..e900a797cc7 100644
--- a/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
@@ -136,7 +136,11 @@ public:
     LLVM_DEBUG(dbgs() << "Checking DILocation from " << *CurrInst
                       << " was copied to " << MI);
 #endif
-    assert(CurrInst->getDebugLoc() == MI.getDebugLoc() &&
+    // We allow insts in the entry block to have a debug loc line of 0 because
+    // they could have originated from constants, and we don't want a jumpy
+    // debug experience.
+    assert((CurrInst->getDebugLoc() == MI.getDebugLoc() ||
+            MI.getDebugLoc().getLine() == 0) &&
            "Line info was not transferred to all instructions");
   }
 };
@@ -1713,8 +1717,15 @@ bool IRTranslator::valueIsSplit(const Value &V,
 
 bool IRTranslator::translate(const Instruction &Inst) {
   CurBuilder->setDebugLoc(Inst.getDebugLoc());
-  EntryBuilder->setDebugLoc(Inst.getDebugLoc());
-  switch(Inst.getOpcode()) {
+  // We only emit constants into the entry block from here. To prevent jumpy
+  // debug behaviour set the line to 0.
+  if (const DebugLoc &DL = Inst.getDebugLoc())
+    EntryBuilder->setDebugLoc(
+        DebugLoc::get(0, 0, DL.getScope(), DL.getInlinedAt()));
+  else
+    EntryBuilder->setDebugLoc(DebugLoc());
+
+  switch (Inst.getOpcode()) {
 #define HANDLE_INST(NUM, OPCODE, CLASS)                                        \
   case Instruction::OPCODE:                                                    \
     return translate##OPCODE(Inst, *CurBuilder.get());