Tighten heuristic for coroutine debug info workaround.

The OutermostLoad condition is supposed to strip the outermost
DW_OP_deref operation because dbg.declares are implicitly
indirect. This patch makes sure the heuristic is only applied to
dbg.declare intrinsics and only if the outermost instruction is a
load.

This was found while qualifying the latest Swift compiler rebranch.

rdar://82037764

llvm/lib/Transforms/Coroutines/CoroFrame.cpp

@@ -2511,7 +2511,7 @@ void coro::salvageDebugInfo(
   DIExpression *Expr = DVI->getExpression();
   // Follow the pointer arithmetic all the way to the incoming
   // function argument and convert into a DIExpression.
-  bool OutermostLoad = true;
+  bool SkipOutermostLoad = !isa<DbgValueInst>(DVI);
   Value *Storage = DVI->getVariableLocationOp(0);
   Value *OriginalStorage = Storage;
   while (auto *Inst = dyn_cast_or_null<Instruction>(Storage)) {
@@ -2523,9 +2523,8 @@ void coro::salvageDebugInfo(
       // implicitly a memory location no DW_OP_deref operation for the
       // last direct load from an alloca is necessary.  This condition
       // effectively drops the *last* DW_OP_deref in the expression.
-      if (!OutermostLoad)
+      if (!SkipOutermostLoad)
         Expr = DIExpression::prepend(Expr, DIExpression::DerefBefore);
-      OutermostLoad = false;
     } else if (auto *StInst = dyn_cast<StoreInst>(Inst)) {
       Storage = StInst->getOperand(0);
     } else {
@@ -2542,6 +2541,7 @@ void coro::salvageDebugInfo(
       Storage = Op;
       Expr = DIExpression::appendOpsToArg(Expr, Ops, 0, /*StackValue*/ false);
     }
+    SkipOutermostLoad = false;
   }
   if (!Storage)
     return;

llvm/test/Transforms/Coroutines/coro-debug.ll

@@ -35,6 +35,7 @@ sw.bb:                                            ; preds = %entry
   call void @llvm.dbg.declare(metadata i32* %x.addr, metadata !12, metadata !13), !dbg !14
   call void @llvm.dbg.declare(metadata i8** %coro_hdl, metadata !15, metadata !13), !dbg !16
   call void @llvm.dbg.declare(metadata i32* %late_local, metadata !29, metadata !13), !dbg !16
+  call void @llvm.dbg.value(metadata i32 %direct, metadata !30, metadata !13), !dbg !14
   ; don't crash when encountering nonsensical debug info, verfifier doesn't yet reject these
   call void @llvm.dbg.declare(metadata i8* null, metadata !28, metadata !13), !dbg !16
   call void @llvm.dbg.declare(metadata !{}, metadata !28, metadata !13), !dbg !16
@@ -68,6 +69,9 @@ coro_Suspend:                                     ; preds = %coro_Cleanup, %sw.d
   ret i8* %8, !dbg !24
 }
 
+; Function Attrs: nounwind readnone speculatable
+declare void @llvm.dbg.value(metadata, metadata, metadata) #1
+
 ; Function Attrs: nounwind readnone speculatable
 declare void @llvm.dbg.declare(metadata, metadata, metadata) #1
 
@@ -146,6 +150,7 @@ attributes #7 = { noduplicate }
 !27 = !DILocalVariable(name: "undefined", scope: !6, file: !7, line: 55, type: !11)
 !28 = !DILocalVariable(name: "null", scope: !6, file: !7, line: 55, type: !11)
 !29 = !DILocalVariable(name: "partial_dead", scope: !6, file: !7, line: 55, type: !11)
+!30 = !DILocalVariable(name: "direct_value", scope: !6, file: !7, line: 55, type: !11)
 
 ; CHECK: define i8* @f(i32 %x) #0 !dbg ![[ORIG:[0-9]+]]
 ; CHECK: define internal fastcc void @f.resume(%f.Frame* noalias nonnull align 8 dereferenceable(32) %FramePtr) #0 !dbg ![[RESUME:[0-9]+]]
@@ -160,6 +165,7 @@ attributes #7 = { noduplicate }
 ; Note that keeping the undef value here could be acceptable, too.
 ; CHECK-NOT: call void @llvm.dbg.declare(metadata i32* undef, metadata !{{[0-9]+}}, metadata !DIExpression())
 ; CHECK: call void @coro.devirt.trigger(i8* null)
+; CHECK: call void @llvm.dbg.value(metadata %f.Frame** {{.*}}, metadata ![[RESUME_DIRECT_VALUE:[0-9]+]], metadata !DIExpression(DW_OP_deref, DW_OP_plus_uconst, {{[0-9]+}}, DW_OP_deref))
 ; CHECK: define internal fastcc void @f.destroy(%f.Frame* noalias nonnull align 8 dereferenceable(32) %FramePtr) #0 !dbg ![[DESTROY:[0-9]+]]
 ; CHECK: define internal fastcc void @f.cleanup(%f.Frame* noalias nonnull align 8 dereferenceable(32) %FramePtr) #0 !dbg ![[CLEANUP:[0-9]+]]
 
@@ -170,6 +176,7 @@ attributes #7 = { noduplicate }
 ; CHECK: ![[RESUME_X]] = !DILocalVariable(name: "x", arg: 1, scope: ![[RESUME]]
 ; CHECK: ![[RESUME_DIRECT]] = !DILocalVariable(name: "direct_mem", scope: ![[RESUME]]
 ; CHECK: ![[RESUME_CONST]] = !DILocalVariable(name: "direct_const", scope: ![[RESUME]]
+; CHECK: ![[RESUME_DIRECT_VALUE]] = !DILocalVariable(name: "direct_value", scope: ![[RESUME]]
 
 ; CHECK: ![[DESTROY]] = distinct !DISubprogram(name: "f", linkageName: "flink"