Add support for ARM modified-immediate assembly syntax.

Certain ARM instructions accept 32-bit immediate operands encoded as a 8-bit
integer value (0-255) and a 4-bit rotation (0-30, even). Current ARM assembly
syntax support in LLVM allows the decoded (32-bit) immediate to be specified
as a single immediate operand for such instructions:

mov r0, #4278190080

The ARMARM defines an extended assembly syntax allowing the encoding to be made
more explicit, as in:

mov r0, #255, #8 ; (same 32-bit value as above)

The behaviour of the two instructions can be different w.r.t flags, which is
documented under "Modified immediate constants" in ARMARM. This patch enables
support for this extended syntax at the MC layer.

llvm-svn: 223113

1 files changed, 35 insertions, 1 deletions

diff --git a/llvm/lib/Target/ARM/ARMMCInstLower.cpp b/llvm/lib/Target/ARM/ARMMCInstLower.cpp
index 023f5f8e37a..fd4f5ff3f20 100644
--- a/llvm/lib/Target/ARM/ARMMCInstLower.cpp
+++ b/llvm/lib/Target/ARM/ARMMCInstLower.cpp
@@ -119,11 +119,45 @@ void llvm::LowerARMMachineInstrToMCInst(const MachineInstr *MI, MCInst &OutMI,
                                         ARMAsmPrinter &AP) {
   OutMI.setOpcode(MI->getOpcode());
 
+  // In the MC layer, we keep modified immediates in their encoded form
+  bool EncodeImms = false;
+  switch (MI->getOpcode()) {
+  default: break;
+  case ARM::MOVi:
+  case ARM::MVNi:
+  case ARM::CMPri:
+  case ARM::CMNri:
+  case ARM::TSTri:
+  case ARM::TEQri:
+  case ARM::MSRi:
+  case ARM::ADCri:
+  case ARM::ADDri:
+  case ARM::ADDSri:
+  case ARM::SBCri:
+  case ARM::SUBri:
+  case ARM::SUBSri:
+  case ARM::ANDri:
+  case ARM::ORRri:
+  case ARM::EORri:
+  case ARM::BICri:
+  case ARM::RSBri:
+  case ARM::RSBSri:
+  case ARM::RSCri:
+    EncodeImms = true;
+    break;
+  }
+
   for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
     const MachineOperand &MO = MI->getOperand(i);
 
     MCOperand MCOp;
-    if (AP.lowerOperand(MO, MCOp))
+    if (AP.lowerOperand(MO, MCOp)) {
+      if (MCOp.isImm() && EncodeImms) {
+        int32_t Enc = ARM_AM::getSOImmVal(MCOp.getImm());
+        if (Enc != -1)
+          MCOp.setImm(Enc);
+      }
       OutMI.addOperand(MCOp);
+    }
   }
 }