[MC] Avoid inlining constant symbols with variants.

[niravd]

Summary

Defer unnecessary early inlining of constants to symbol
variants. Fixes PR38945.

[rnk]

lgtm

[nickdesaulniers]

llvm/lib/MC/MCParser/AsmParser.cpp

1128 ↗

(On Diff #165812)

I'm not super enthused about relying on the enum's value being zero as opposed to checking that Variant == MCSymbolRefExpr::VK_None, but it looks like it's done so anyways on L1132, so I guess it's fine.

llvm/test/MC/PowerPC/pr38945.s

9 ↗

(On Diff #165812)

Can you add a test for the - prefix for negating the number, too (assuming it works and doesn't need additional code changed)?

ie

cmpwi 8,(-NUMBER)@l
cmpwi 8,-NUMBER@l

llvm/trunk/lib/MC/MCParser/AsmParser.cpp

case AsmToken::Identifier: {
     }
 
     MCSymbol *Sym = getContext().getOrCreateSymbol(SymbolName);
 
     // If this is an absolute variable reference, substitute it now to preserve
     // semantics in the face of reassignment.
     if (Sym->isVariable()) {
       auto V = Sym->getVariableValue(/*SetUsed*/ false);
-      bool DoInline = isa<MCConstantExpr>(V);
+      bool DoInline = isa<MCConstantExpr>(V) && !Variant;
       if (auto TV = dyn_cast<MCTargetExpr>(V))
         DoInline = TV->inlineAssignedExpr();
       if (DoInline) {
         if (Variant)
           return Error(EndLoc, "unexpected modifier on variable reference");
         Res = Sym->getVariableValue(/*SetUsed*/ false);
         return false;
       }

llvm/trunk/test/MC/PowerPC/pr38945.s

+// RUN: llvm-mc -triple=powerpc64-pc-linux %s -o - | FileCheck %s
+
+NUMBER = 0x6ffffff9
+
+        .text
+.globl  main
+main:
+  cmpwi   8,(NUMBER)@l
+  cmpwi   8,-(NUMBER)@l
+  cmpwi   8,(-NUMBER)@l
+  cmpwi   8,NUMBER@l
+  cmpwi   8,-NUMBER@l
+
+
+// CHECK: main:
+// CHECK: cmpwi 8, -7
+// CHECK: cmpwi 8, 7
+// CHECK: cmpwi 8, 7
+// CHECK: cmpwi 8, -7
+// CHECK: cmpwi 8, 7
+