[PATCH] D47545: [MC][X86] Allow assembler variable assignment to register name.

[Reid Kleckner via Phabricator via llvm-commits]

rnk added inline comments.


================
Comment at: llvm/lib/MC/MCParser/AsmParser.cpp:1114-1121
     // If this is an absolute variable reference, substitute it now to preserve
     // semantics in the face of reassignment.
-    if (Sym->isVariable() &&
-        isa<MCConstantExpr>(Sym->getVariableValue(/*SetUsed*/ false))) {
-      if (Variant)
-        return Error(EndLoc, "unexpected modifier on variable reference");
-
-      Res = Sym->getVariableValue(/*SetUsed*/ false);
-      return false;
+    if (Sym->isVariable()) {
+      auto V = Sym->getVariableValue(/*SetUsed*/ false);
+      bool DoInline = isa<MCConstantExpr>(V);
+      if (auto TV = dyn_cast<MCTargetExpr>(V))
+        DoInline = TV->inlineAssignedExpr();
----------------
Given that we already have logic like this, I'm OK with this. I guess gnu as treats `=` assignments much more textually than we do.


================
Comment at: llvm/lib/Target/X86/AsmParser/X86AsmParser.cpp:2197
+    SMLoc StartLoc = Parser.getTok().getLoc();
+    // Normal Expression parse fails, check if it could be a register.
+    unsigned RegNo;
----------------
Does this generalize to more than just registers? Could it include things like `foo = $42`, or `foo = 0x40(%rcx)` as some kind of alias for an accessor? We might want to allow these things so that we don't have to do this fire drill again the next time a Linux developer writes some creative GNU as.


Repository:
  rL LLVM

https://reviews.llvm.org/D47545