[AArch64] Support "S" inline assembler constraint

This patch re-introduces the "S" inline assembler constraint. This matches
an absolute symbolic address or a label reference. The primary use case is

asm("adrp %0, %1\n\t"
    "add %0, %0, :lo12:%1" : "=r"(addr) : "S"(&var));

I say re-introduces as it seems like "S" was implemented in the original
AArch64 backend, but it looks like it wasn't carried forward to the merged
backend. The original implementation had A and L modifiers that could be
used to print ":lo12:" to the string. It looks like gcc doesn't use these
and :lo12: is expected to be written in the inline assembly string so I've
not implemented A and L. Clang already supports the S modifier.

Fixes PR37180

Differential Revision: https://reviews.llvm.org/D46745

llvm-svn: 332444

2 files changed, 25 insertions, 1 deletions

diff --git a/llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp b/llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp
index 7788fa5d3cc..f5ee0c46c07 100644
--- a/llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp
+++ b/llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp
@@ -276,6 +276,11 @@ void AArch64AsmPrinter::printOperand(const MachineInstr *MI, unsigned OpNum,
     printOffset(MO.getOffset(), O);
     break;
   }
+  case MachineOperand::MO_BlockAddress: {
+    MCSymbol *Sym = GetBlockAddressSymbol(MO.getBlockAddress());
+    Sym->print(O, MAI);
+    break;
+  }
   }
 }
 
diff --git a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
index 51063ee7fb4..b5b65e0b817 100644
--- a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -5212,7 +5212,7 @@ SDValue AArch64TargetLowering::getRecipEstimate(SDValue Operand,
 
 // Table of Constraints
 // TODO: This is the current set of constraints supported by ARM for the
-// compiler, not all of them may make sense, e.g. S may be difficult to support.
+// compiler, not all of them may make sense.
 //
 // r - A general register
 // w - An FP/SIMD register of some size in the range v0-v31
@@ -5272,6 +5272,8 @@ AArch64TargetLowering::getConstraintType(StringRef Constraint) const {
     // currently handle addresses it is the same as 'r'.
     case 'Q':
       return C_Memory;
+    case 'S': // A symbolic address
+      return C_Other;
     }
   }
   return TargetLowering::getConstraintType(Constraint);
@@ -5396,6 +5398,23 @@ void AArch64TargetLowering::LowerAsmOperandForConstraint(
       Result = DAG.getRegister(AArch64::WZR, MVT::i32);
     break;
   }
+  case 'S': {
+    // An absolute symbolic address or label reference.
+    if (const GlobalAddressSDNode *GA = dyn_cast<GlobalAddressSDNode>(Op)) {
+      Result = DAG.getTargetGlobalAddress(GA->getGlobal(), SDLoc(Op),
+                                          GA->getValueType(0));
+    } else if (const BlockAddressSDNode *BA =
+                   dyn_cast<BlockAddressSDNode>(Op)) {
+      Result =
+          DAG.getTargetBlockAddress(BA->getBlockAddress(), BA->getValueType(0));
+    } else if (const ExternalSymbolSDNode *ES =
+                   dyn_cast<ExternalSymbolSDNode>(Op)) {
+      Result =
+          DAG.getTargetExternalSymbol(ES->getSymbol(), ES->getValueType(0));
+    } else
+      return;
+    break;
+  }
 
   case 'I':
   case 'J':