[cherry-pick][SelectionDAG] Disable FastISel for swiftasync functions (#70741)

llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp

@@ -204,6 +204,16 @@ static RegisterScheduler
 defaultListDAGScheduler("default", "Best scheduler for the target",
                         createDefaultScheduler);
 
+static bool dontUseFastISelFor(const Function &Fn) {
+  // Don't enable FastISel for functions with swiftasync Arguments.
+  // Debug info on those is reliant on good Argument lowering, and FastISel is
+  // not capable of lowering the entire function. Mixing the two selectors tend
+  // to result in poor lowering of Arguments.
+  return any_of(Fn.args(), [](const Argument &Arg) {
+    return Arg.hasAttribute(Attribute::AttrKind::SwiftAsync);
+  });
+}
+
 namespace llvm {
 
   //===--------------------------------------------------------------------===//
@@ -219,21 +229,22 @@ namespace llvm {
                     CodeGenOpt::Level NewOptLevel) : IS(ISel) {
       SavedOptLevel = IS.OptLevel;
       SavedFastISel = IS.TM.Options.EnableFastISel;
-      if (NewOptLevel == SavedOptLevel)
-        return;
-      IS.OptLevel = NewOptLevel;
-      IS.TM.setOptLevel(NewOptLevel);
-      LLVM_DEBUG(dbgs() << "\nChanging optimization level for Function "
-                        << IS.MF->getFunction().getName() << "\n");
-      LLVM_DEBUG(dbgs() << "\tBefore: -O" << SavedOptLevel << " ; After: -O"
-                        << NewOptLevel << "\n");
-      if (NewOptLevel == CodeGenOpt::None) {
-        IS.TM.setFastISel(IS.TM.getO0WantsFastISel());
-        LLVM_DEBUG(
-            dbgs() << "\tFastISel is "
-                   << (IS.TM.Options.EnableFastISel ? "enabled" : "disabled")
-                   << "\n");
+      if (NewOptLevel != SavedOptLevel) {
+        IS.OptLevel = NewOptLevel;
+        IS.TM.setOptLevel(NewOptLevel);
+        LLVM_DEBUG(dbgs() << "\nChanging optimization level for Function "
+                          << IS.MF->getFunction().getName() << "\n");
+        LLVM_DEBUG(dbgs() << "\tBefore: -O" << SavedOptLevel << " ; After: -O"
+                          << NewOptLevel << "\n");
+        if (NewOptLevel == CodeGenOpt::None)
+          IS.TM.setFastISel(IS.TM.getO0WantsFastISel());
       }
+      if (dontUseFastISelFor(IS.MF->getFunction()))
+        IS.TM.setFastISel(false);
+      LLVM_DEBUG(
+          dbgs() << "\tFastISel is "
+                 << (IS.TM.Options.EnableFastISel ? "enabled" : "disabled")
+                 << "\n");
     }
 
     ~OptLevelChanger() {

llvm/test/CodeGen/X86/swift-async-no-fastisel.ll

@@ -0,0 +1,40 @@
+; RUN: llc %s --fast-isel=true --stop-after=finalize-isel -o %t \
+; RUN:   -experimental-debug-variable-locations=false --global-isel=false
+; RUN:   FileCheck %s < %t
+; RUN:   FileCheck %s --check-prefix=INTRINSICS < %t
+
+
+source_filename = "ir_x86.ll"
+target triple = "x86_64-*"
+
+define swifttailcc void @foo(ptr swiftasync %0) !dbg !43 {
+  call void asm sideeffect "", "r"(ptr %0), !dbg !62
+  ; FastISEL doesn't preserve %0 here. Check that this function is lowered with SelectionDAG.
+  call void @llvm.dbg.value(metadata ptr %0, metadata !54, metadata !DIExpression(DW_OP_plus_uconst, 4242)), !dbg !62
+  ret void, !dbg !62
+}
+
+; CHECK-NOT: DBG_VALUE $noreg
+; INTRINSICS: ![[VAR:[0-9]*]] = !DILocalVariable(name: "msg",
+; INTRINSICS: DBG_VALUE {{.*}}, ![[VAR]], !DIExpression(DW_OP_plus_uconst, 4242)
+
+
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+!llvm.module.flags = !{!6, !7, !8, !9, !10}
+!llvm.dbg.cu = !{!16}
+
+!6 = !{i32 7, !"Dwarf Version", i32 4}
+!7 = !{i32 2, !"Debug Info Version", i32 3}
+!8 = !{i32 1, !"wchar_size", i32 4}
+!9 = !{i32 8, !"PIC Level", i32 2}
+!10 = !{i32 7, !"uwtable", i32 2}
+!16 = distinct !DICompileUnit(language: DW_LANG_Swift, file: !17, producer: "blah", emissionKind: FullDebug)
+!17 = !DIFile(filename: "blah", directory: "blah")
+!43 = distinct !DISubprogram(name: "blah", linkageName: "blah", file: !17, line: 87, type: !44, scopeLine: 87, unit: !16, retainedNodes: !48)
+!44 = !DISubroutineType(types: !45)
+!45 = !{!46}
+!46 = !DICompositeType(tag: DW_TAG_structure_type, name: "blah")
+!48 = !{!54}
+!54 = !DILocalVariable(name: "msg", arg: 1, scope: !43, file: !17, line: 87, type: !46)
+!62 = !DILocation(line: 87, column: 30, scope: !43)