1 files changed, 21 insertions, 11 deletions

diff --git a/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp b/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
index 1e661d82dad..4ccadf915cc 100644
--- a/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
+++ b/llvm/lib/Target/ARM/AsmParser/ARMAsmParser.cpp
@@ -4419,9 +4419,8 @@ ARMAsmParser::parseModImm(OperandVector &Operands) {
   int64_t Imm1, Imm2;
 
   if ((Parser.getTok().isNot(AsmToken::Hash) &&
-       Parser.getTok().isNot(AsmToken::Dollar) /* looking for an immediate */ )
-      || Lexer.peekTok().is(AsmToken::Colon)
-      || Lexer.peekTok().is(AsmToken::LParen) /* avoid complex operands */ )
+       Parser.getTok().isNot(AsmToken::Dollar))
+      || Lexer.peekTok().is(AsmToken::Colon))
     return MatchOperand_NoMatch;
 
   SMLoc S = Parser.getTok().getLoc();
@@ -4440,7 +4439,7 @@ ARMAsmParser::parseModImm(OperandVector &Operands) {
   const MCConstantExpr *CE = dyn_cast<MCConstantExpr>(Imm1Exp);
 
   if (CE) {
-    // immediate must fit within 32-bits
+    // Immediate must fit within 32-bits
     Imm1 = CE->getValue();
     if (Imm1 < INT32_MIN || Imm1 > UINT32_MAX) {
       Error(Sx1, "immediate operand must be representable with 32 bits");
@@ -4455,19 +4454,30 @@ ARMAsmParser::parseModImm(OperandVector &Operands) {
                                                   Sx1, Ex1));
       return MatchOperand_Success;
     }
-  } else {
-    Error(Sx1, "constant expression expected");
-    return MatchOperand_ParseFail;
-  }
 
-  if (Parser.getTok().isNot(AsmToken::Comma)) {
-    // Consider [mov r0, #-10], which is aliased with mvn. We cannot fail
-    // the parse here.
+    // We have parsed an immediate which is not for us, fallback to a plain
+    // immediate. This can happen for instruction aliases. For an example,
+    // ARMInstrInfo.td defines the alias [mov <-> mvn] which can transform
+    // a mov (mvn) with a mod_imm_neg/mod_imm_not operand into the opposite
+    // instruction with a mod_imm operand. The alias is defined such that the
+    // parser method is shared, that's why we have to do this here.
+    if (Parser.getTok().is(AsmToken::EndOfStatement)) {
+      Operands.push_back(ARMOperand::CreateImm(Imm1Exp, Sx1, Ex1));
+      return MatchOperand_Success;
+    }
+  } else {
+    // Operands like #(l1 - l2) can only be evaluated at a later stage (via an
+    // MCFixup). Fallback to a plain immediate.
     Operands.push_back(ARMOperand::CreateImm(Imm1Exp, Sx1, Ex1));
     return MatchOperand_Success;
   }
 
   // From this point onward, we expect the input to be a (#bits, #rot) pair
+  if (Parser.getTok().isNot(AsmToken::Comma)) {
+    Error(Sx1, "expected modified immediate operand: #[0, 255], #even[0-30]");
+    return MatchOperand_ParseFail;
+  }
+
   if (Imm1 & ~0xFF) {
     Error(Sx1, "immediate operand must a number in the range [0, 255]");
     return MatchOperand_ParseFail;