[Instruction] Add updateLocationAfterHoist helper

Introduce a helper on Instruction which can be used to update the debug
location after hoisting.

Use this in GVN and LICM, where we were mistakenly introducing new line
0 locations after hoisting (the docs recommend dropping the location in
this case).

For more context, see the discussion in https://reviews.llvm.org/D60913.

Differential Revision: https://reviews.llvm.org/D85670

include/llvm/IR/Instruction.h

@@ -492,6 +492,10 @@ public:
   /// merged DebugLoc.
   void applyMergedLocation(const DILocation *LocA, const DILocation *LocB);
 
+  /// Updates the debug location given that the instruction has been hoisted
+  /// from a block to a predecessor of that block.
+  void updateLocationAfterHoist();
+
 private:
   /// Return true if we have an entry in the on-the-side metadata hash.
   bool hasMetadataHashEntry() const {

lib/IR/DebugInfo.cpp

@@ -696,6 +696,24 @@ void Instruction::applyMergedLocation(const DILocation *LocA,
   setDebugLoc(DILocation::getMergedLocation(LocA, LocB));
 }
 
+void Instruction::updateLocationAfterHoist() {
+  const DebugLoc &DL = getDebugLoc();
+  if (!DL)
+    return;
+
+  // If we didn't hoist a call, drop the location to allow a location from a
+  // preceding instruction to propagate.
+  if (!isa<CallBase>(this)) {
+    setDebugLoc(DebugLoc());
+    return;
+  }
+
+  // Set a line 0 location for (potentially inlinable) calls. Set the scope to
+  // the parent function's scope if it's available, and drop any inlinedAt info
+  // to avoid making it look like the inlined callee was reached early.
+  setDebugLoc(DebugLoc::get(0, 0, DL.getScope()));
+}
+
 //===----------------------------------------------------------------------===//
 // LLVM C API implementations.
 //===----------------------------------------------------------------------===//

lib/Transforms/Scalar/GVN.cpp

@@ -46,7 +46,6 @@
 #include "llvm/IR/Constant.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DataLayout.h"
-#include "llvm/IR/DebugInfoMetadata.h"
 #include "llvm/IR/DebugLoc.h"
 #include "llvm/IR/Dominators.h"
 #include "llvm/IR/Function.h"
@@ -1314,8 +1313,7 @@ bool GVN::PerformLoadPRE(LoadInst *LI, AvailValInBlkVect &ValuesPerBlock,
     // 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.
-    if (const DebugLoc &DL = I->getDebugLoc())
-      I->setDebugLoc(DebugLoc::get(0, 0, DL.getScope(), DL.getInlinedAt()));
+    I->updateLocationAfterHoist();
 
     // FIXME: We really _ought_ to insert these value numbers into their
     // parent's availability map.  However, in doing so, we risk getting into

lib/Transforms/Scalar/LICM.cpp

@@ -1658,10 +1658,7 @@ static void hoist(Instruction &I, const DominatorTree *DT, const Loop *CurLoop,
     // Move the new node to the destination block, before its terminator.
     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.
-  if (const DebugLoc &DL = I.getDebugLoc())
-    I.setDebugLoc(DebugLoc::get(0, 0, DL.getScope(), DL.getInlinedAt()));
+  I.updateLocationAfterHoist();
 
   if (isa<LoadInst>(I))
     ++NumMovedLoads;

test/DebugInfo/Generic/licm-hoist-debug-loc.ll

@@ -18,9 +18,8 @@
 ; We make sure that the instruction that is hoisted into the preheader
 ; does not have a debug location.
 ; CHECK: for.body.lr.ph:
-; CHECK: getelementptr{{.*}}%p.addr, i64 4{{.*}} !dbg [[zero:![0-9]+]]
+; CHECK: getelementptr{{.*}}%p.addr, i64 4{{$}}
 ; CHECK: for.body:
-; CHECK: [[zero]] = !DILocation(line: 0
 ;
 ; ModuleID = 't.ll'
 source_filename = "test.c"

test/Transforms/GVN/PRE/phi-translate.ll

@@ -4,8 +4,8 @@ target datalayout = "e-p:64:64:64"
 
 ; CHECK-LABEL: @foo(
 ; CHECK: entry.end_crit_edge:
-; CHECK: %[[INDEX:[a-z0-9.]+]] = sext i32 %x to i64{{.*}} !dbg [[ZERO_LOC:![0-9]+]]
-; CHECK: %[[ADDRESS:[a-z0-9.]+]] = getelementptr [100 x i32], [100 x i32]* @G, i64 0, i64 %[[INDEX]]{{.*}} !dbg [[ZERO_LOC]]
+; CHECK: %[[INDEX:[a-z0-9.]+]] = sext i32 %x to i64{{$}}
+; CHECK: %[[ADDRESS:[a-z0-9.]+]] = getelementptr [100 x i32], [100 x i32]* @G, i64 0, i64 %[[INDEX]]{{$}}
 ; CHECK:   %n.pre = load i32, i32* %[[ADDRESS]], align 4, !dbg [[N_LOC:![0-9]+]]
 ; CHECK: br label %end
 ; CHECK: then:
@@ -14,8 +14,7 @@ target datalayout = "e-p:64:64:64"
 ; CHECK:   %n = phi i32 [ %n.pre, %entry.end_crit_edge ], [ %z, %then ], !dbg [[N_LOC]]
 ; CHECK:   ret i32 %n
 
-; CHECK-DAG: [[N_LOC]] = !DILocation(line: 47, column: 1, scope: !{{.*}})
-; CHECK-DAG: [[ZERO_LOC]] = !DILocation(line: 0
+; CHECK: [[N_LOC]] = !DILocation(line: 47, column: 1, scope: !{{.*}})
 
 @G = external global [100 x i32]
 define i32 @foo(i32 %x, i32 %z) !dbg !6 {

test/Transforms/LICM/hoisting-preheader-debugloc.ll

@@ -1,6 +1,6 @@
 ; RUN: opt -S -licm < %s | FileCheck %s
 
-; CHECK: %arrayidx4.promoted = load i32, i32* %arrayidx4, align 1, !tbaa !59
+; CHECK: %arrayidx4.promoted = load i32, i32* %arrayidx4, align 1, !tbaa !{{[0-9]+$}}
 
 target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"

unittests/IR/InstructionsTest.cpp

@@ -1304,5 +1304,52 @@ TEST(InstructionsTest, UnaryOperator) {
   I->deleteValue();
 }
 
+TEST(InstructionsTest, UpdateLocationAfterHoist) {
+  LLVMContext C;
+  std::unique_ptr<Module> M = parseIR(C,
+                                      R"(
+      declare void @callee()
+
+      define void @f() {
+        call void @callee()           ; Inst with no location.
+        call void @callee(), !dbg !11 ; Call with location.
+        ret void, !dbg !11            ; Non-call inst with location.
+      }
+
+      !llvm.dbg.cu = !{!0}
+      !llvm.module.flags = !{!3, !4}
+      !0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 6.0.0", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+      !1 = !DIFile(filename: "t2.c", directory: "foo")
+      !2 = !{}
+      !3 = !{i32 2, !"Dwarf Version", i32 4}
+      !4 = !{i32 2, !"Debug Info Version", i32 3}
+      !8 = distinct !DISubprogram(name: "f", scope: !1, file: !1, line: 1, type: !9, isLocal: false, isDefinition: true, scopeLine: 1, isOptimized: false, unit: !0, retainedNodes: !2)
+      !9 = !DISubroutineType(types: !10)
+      !10 = !{null}
+      !11 = !DILocation(line: 2, column: 7, scope: !8)
+  )");
+  ASSERT_TRUE(M);
+  Function *F = cast<Function>(M->getNamedValue("f"));
+  BasicBlock &BB = F->front();
+
+  auto *I1 = BB.getFirstNonPHI();
+  auto *I2 = I1->getNextNode();
+  auto *I3 = BB.getTerminator();
+
+  EXPECT_FALSE(bool(I1->getDebugLoc()));
+  I1->updateLocationAfterHoist();
+  EXPECT_FALSE(bool(I1->getDebugLoc()));
+
+  const MDNode *Scope = I2->getDebugLoc().getScope();
+  EXPECT_EQ(I2->getDebugLoc().getLine(), 2U);
+  I2->updateLocationAfterHoist();
+  EXPECT_EQ(I2->getDebugLoc().getLine(), 0U);
+  EXPECT_EQ(I2->getDebugLoc().getScope(), Scope);
+
+  EXPECT_EQ(I3->getDebugLoc().getLine(), 2U);
+  I3->updateLocationAfterHoist();
+  EXPECT_FALSE(bool(I3->getDebugLoc()));
+}
+
 } // end anonymous namespace
 } // end namespace llvm