[MC] [AArch64] Correctly resolve ":abs_g1:3" etc.

[efriedma]

Summary

We have to treat constructs like this as if they were "symbolic", to use the correct codepath to resolve them This mostly only affects movz etc. because the other uses of classifySymbolRef conservatively treat everything that isn't a constant as if it were a symbol.

Depends on D55896.

[mstorsjo]

LGTM

[peter.smith]

LGTM as well

[mgrang]

LGTM. I have verified that this patch fixes the error if the label is defined before the use (mentioned in D55896).

llvm/trunk/lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp

if (SE) {
     // It's a simple symbol reference with no addend.
     DarwinRefKind = SE->getKind();
     return true;
   }
 
   // Check that it looks like a symbol + an addend
   MCValue Res;
   bool Relocatable = Expr->evaluateAsRelocatable(Res, nullptr, nullptr);
-  if (!Relocatable || !Res.getSymA() || Res.getSymB())
+  if (!Relocatable || Res.getSymB())
     return false;
 
+  // Treat expressions with an ELFRefKind (like ":abs_g1:3", or
+  // ":abs_g1:x" where x is constant) as symbolic even if there is no symbol.
+  if (!Res.getSymA() && ELFRefKind == AArch64MCExpr::VK_INVALID)
+    return false;
+
+  if (Res.getSymA())
     DarwinRefKind = Res.getSymA()->getKind();
   Addend = Res.getConstant();
 
   // It's some symbol reference + a constant addend, but really
   // shouldn't use both Darwin and ELF syntax.
   return ELFRefKind == AArch64MCExpr::VK_INVALID ||
          DarwinRefKind == MCSymbolRefExpr::VK_None;
 }
 

llvm/trunk/test/MC/AArch64/fixup-absolute.s

 // RUN: llvm-mc -triple aarch64--none-eabi -filetype obj < %s -o - | llvm-objdump -d - | FileCheck %s
 
+onepart_before = 0x1234
+twopart_before = 0x12345678
+threepart_before = 0x1234567890AB
+fourpart_before = 0x1234567890ABCDEF
+
+// CHECK: mov     x0, #1311673391471656960
 // CHECK: mov     x0, #1311673391471656960
-movz x0, #:abs_g3:fourpart
+movz x0, #:abs_g3:fourpart_before
+movz x0, #:abs_g3:fourpart_after
 // CHECK: mov     x0, #20014547599360
-movz x0, #:abs_g2:threepart
+// CHECK: mov     x0, #20014547599360
+movz x0, #:abs_g2:threepart_before
+movz x0, #:abs_g2:threepart_after
+// CHECK: movk    x0, #22136, lsl #32
 // CHECK: movk    x0, #22136, lsl #32
-movk x0, #:abs_g2_nc:fourpart
+movk x0, #:abs_g2_nc:fourpart_before
+movk x0, #:abs_g2_nc:fourpart_after
 // CHECK: mov     x0, #305397760
-movz x0, #:abs_g1:twopart
+// CHECK: mov     x0, #305397760
+movz x0, #:abs_g1:twopart_before
+movz x0, #:abs_g1:twopart_after
+// CHECK: movk    x0, #37035, lsl #16
 // CHECK: movk    x0, #37035, lsl #16
-movk x0, #:abs_g1_nc:fourpart
+movk x0, #:abs_g1_nc:fourpart_before
+movk x0, #:abs_g1_nc:fourpart_after
 // CHECK: mov     x0, #4660
-movz x0, #:abs_g0:onepart
+// CHECK: mov     x0, #4660
+movz x0, #:abs_g0:onepart_before
+movz x0, #:abs_g0:onepart_after
+// CHECK: movk    x0, #52719
 // CHECK: movk    x0, #52719
-movk x0, #:abs_g0_nc:fourpart
+movk x0, #:abs_g0_nc:fourpart_before
+movk x0, #:abs_g0_nc:fourpart_after
 
-onepart = 0x1234
-twopart = 0x12345678
-threepart = 0x1234567890AB
-fourpart = 0x1234567890ABCDEF
+onepart_after = 0x1234
+twopart_after = 0x12345678
+threepart_after = 0x1234567890AB
+fourpart_after = 0x1234567890ABCDEF