Alternative approach: Allow jumping to D labels in naked DMD-style inline-asm by making them asm labels too

Author: kinke

gen/asmstmt.cpp

@@ -532,10 +532,14 @@ void CompoundAsmStatement_toIR(CompoundAsmStatement *stmt, IRState *p) {
       }
       Identifier *const ident = targetLabel->ident;
 
-      // if the label is defined in inline asm, no special handling is necessary, skip
-      if (fd->asmLabels && llvm::any_of(*fd->asmLabels, [ident](Identifier *i) {
-            return i->equals(ident);
-          })) {
+      // if the label is defined in inline asm, we can jump to it directly
+      if (fd->isNaked() // in naked DMD-style inline-asm functions, all D labels
+                        // become assembly labels too (and the extra forwarding
+                        // code would mess with the stack due to an i32 alloca)
+          || (fd->asmLabels &&
+              llvm::any_of(*fd->asmLabels, [ident](Identifier *i) {
+                return i->equals(ident);
+              }))) {
         continue;
       }
 
@@ -544,18 +548,6 @@ void CompoundAsmStatement_toIR(CompoundAsmStatement *stmt, IRState *p) {
         continue;
       }
 
-      // the extra forwarding code needs an i32 alloca, so messes with the stack
-      if (fd->isNaked()) {
-        error(stmt->loc,
-              "branch to non-assembly D label `%s` not allowed in "
-              "naked inline assembly",
-              ident->toChars());
-        errorSupplemental(
-            stmt->loc,
-            "Either define the label inside an `asm` block, or drop `naked`.");
-        continue;
-      }
-
       // record that the jump needs to be handled in the post-asm dispatcher
       gotoToVal[targetLabel] = n_goto;
 

gen/statements.cpp

@@ -1542,15 +1542,20 @@ class ToIRVisitor : public Visitor {
     auto &PGO = irs->funcGen().pgo;
     PGO.setCurrentStmt(stmt);
 
+    auto fd = irs->func()->decl;
+
+    const auto getFullAsmLabelString = [stmt, fd]() {
+      std::stringstream s;
+      printLabelName(s, mangleExact(fd), stmt->ident->toChars());
+      s << ":";
+      return s.str();
+    };
+
     // if it's an inline asm label, we don't create a basicblock, just emit it
     // in the asm
     if (irs->asmBlock) {
       auto a = new IRAsmStmt;
-      std::stringstream label;
-      printLabelName(label, mangleExact(irs->func()->decl),
-                     stmt->ident->toChars());
-      label << ":";
-      a->code = label.str();
+      a->code = getFullAsmLabelString();
       irs->asmBlock->s.push_back(a);
 
       // disable inlining
@@ -1565,6 +1570,13 @@ class ToIRVisitor : public Visitor {
       }
 
       irs->ir->SetInsertPoint(labelBB);
+
+      // in a naked DMD-style inline-asm function, create an assembly label too
+      // (so that inline-asm can jump to it directly)
+      if (fd->isNaked()) {
+        DtoInlineAsmExpr(stmt->loc, getFullAsmLabelString(), "", {}, {},
+                         irs->ir->getVoidTy());
+      }
     }
 
     PGO.emitCounterIncrement(stmt);