[KeyInstr][Clang] Aggregate init + copy (#134639)

This patch is part of a stack that teaches Clang to generate Key Instructions
metadata for C and C++.

RFC:
https://discourse.llvm.org/t/rfc-improving-is-stmt-placement-for-better-interactive-debugging/82668

The feature is only functional in LLVM if LLVM is built with CMake flag
LLVM_EXPERIMENTAL_KEY_INSTRUCTIONs. Eventually that flag will be removed.

Author: OCHyams

clang/lib/CodeGen/CGDebugInfo.h

@@ -892,20 +892,6 @@ class CGDebugInfo {
   }
 };
 
-/// A scoped helper to set the current source atom group for
-/// CGDebugInfo::addInstToCurrentSourceAtom. A source atom is a source construct
-/// that is "interesting" for debug stepping purposes. We use an atom group
-/// number to track the instruction(s) that implement the functionality for the
-/// atom, plus backup instructions/source locations.
-class ApplyAtomGroup {
-  uint64_t OriginalAtom = 0;
-  CGDebugInfo *DI = nullptr;
-
-public:
-  ApplyAtomGroup(CGDebugInfo *DI);
-  ~ApplyAtomGroup();
-};
-
 /// A scoped helper to set the current debug location to the specified
 /// location or preferred location of the specified Expr.
 class ApplyDebugLocation {

clang/lib/CodeGen/CGExprAgg.cpp

@@ -1332,6 +1332,7 @@ static bool isBlockVarRef(const Expr *E) {
 }
 
 void AggExprEmitter::VisitBinAssign(const BinaryOperator *E) {
+  ApplyAtomGroup Grp(CGF.getDebugInfo());
   // For an assignment to work, the value on the right has
   // to be compatible with the value on the left.
   assert(CGF.getContext().hasSameUnqualifiedType(E->getLHS()->getType(),
@@ -2393,7 +2394,8 @@ void CodeGenFunction::EmitAggregateCopy(LValue Dest, LValue Src, QualType Ty,
     }
   }
 
-  auto Inst = Builder.CreateMemCpy(DestPtr, SrcPtr, SizeVal, isVolatile);
+  auto *Inst = Builder.CreateMemCpy(DestPtr, SrcPtr, SizeVal, isVolatile);
+  addInstToCurrentSourceAtom(Inst, nullptr);
 
   // Determine the metadata to describe the position of any padding in this
   // memcpy, as well as the TBAA tags for the members of the struct, in case

clang/lib/CodeGen/CodeGenFunction.h

@@ -258,6 +258,20 @@ template <> struct DominatingValue<RValue> {
   }
 };
 
+/// A scoped helper to set the current source atom group for
+/// CGDebugInfo::addInstToCurrentSourceAtom. A source atom is a source construct
+/// that is "interesting" for debug stepping purposes. We use an atom group
+/// number to track the instruction(s) that implement the functionality for the
+/// atom, plus backup instructions/source locations.
+class ApplyAtomGroup {
+  uint64_t OriginalAtom = 0;
+  CGDebugInfo *DI = nullptr;
+
+public:
+  ApplyAtomGroup(CGDebugInfo *DI);
+  ~ApplyAtomGroup();
+};
+
 /// CodeGenFunction - This class organizes the per-function state that is used
 /// while generating LLVM code.
 class CodeGenFunction : public CodeGenTypeCache {
@@ -3035,6 +3049,7 @@ class CodeGenFunction : public CodeGenTypeCache {
 
   /// Emit an aggregate assignment.
   void EmitAggregateAssign(LValue Dest, LValue Src, QualType EltTy) {
+    ApplyAtomGroup Grp(getDebugInfo());
     bool IsVolatile = hasVolatileMember(EltTy);
     EmitAggregateCopy(Dest, Src, EltTy, AggValueSlot::MayOverlap, IsVolatile);
   }

clang/test/DebugInfo/KeyInstructions/agg.c

@@ -0,0 +1,17 @@
+// RUN: %clang_cc1 -gkey-instructions -x c++ %s -debug-info-kind=line-tables-only -emit-llvm -o - \
+// RUN: | FileCheck %s --implicit-check-not atomGroup --implicit-check-not atomRank
+
+// RUN: %clang_cc1 -gkey-instructions -x c %s -debug-info-kind=line-tables-only -emit-llvm -o - \
+// RUN: | FileCheck %s --implicit-check-not atomGroup --implicit-check-not atomRank
+
+typedef struct { int a, b, c; } Struct;
+void fun(Struct a) {
+// CHECK: call void @llvm.memcpy{{.*}}, !dbg [[G1R1:!.*]]
+  Struct b = a;
+
+// CHECK: call void @llvm.memcpy{{.*}}, !dbg [[G2R1:!.*]]
+  b = a;
+}
+
+// CHECK: [[G1R1]] = !DILocation({{.*}}, atomGroup: 1, atomRank: 1)
+// CHECK: [[G2R1]] = !DILocation({{.*}}, atomGroup: 2, atomRank: 1)