[TableGen] Prevent invalid code generation when emitting AssemblerPredicate conditions.

Summary:
The loop which emits AssemblerPredicate conditions also links them together by emitting a '&&'.
If the 1st predicate is not an AssemblerPredicate, while the 2nd one is, nothing gets emitted for the 1st one, but we still emit the '&&' because of the 2nd predicate.
This generated code looks like "( && Cond2)" and is invalid.

Reviewers: dsanders

Reviewed By: dsanders

Subscribers: dsanders, llvm-commits

Differential Revision: http://reviews.llvm.org/D8294

llvm-svn: 234312

llvm/test/TableGen/AsmPredicateCondsEmission.td

@@ -0,0 +1,31 @@
+// RUN: llvm-tblgen -gen-disassembler -I %p/../../include %s | FileCheck %s
+
+// Check that we don't generate invalid code of the form "( && Cond2)" when
+// emitting AssemblerPredicate conditions. In the example below, the invalid
+// code would be: "return ( && (Bits & arch::AssemblerCondition2));".
+
+include "llvm/Target/Target.td"
+
+def archInstrInfo : InstrInfo { }
+
+def arch : Target {
+  let InstructionSet = archInstrInfo;
+}
+
+def Pred1 : Predicate<"Condition1">;
+def Pred2 : Predicate<"Condition2">,
+            AssemblerPredicate<"AssemblerCondition2">;
+
+def foo : Instruction {
+  let Size = 2;
+  let OutOperandList = (outs);
+  let InOperandList = (ins);
+  field bits<16> Inst;
+  let Inst = 0xAAAA;
+  let AsmString = "foo";
+  field bits<16> SoftFail = 0;
+  // This is the important bit:
+  let Predicates = [Pred1, Pred2];
+}
+
+// CHECK: return ((Bits & arch::AssemblerCondition2));

llvm/utils/TableGen/FixedLenDecoderEmitter.cpp

@@ -1112,6 +1112,7 @@ bool FilterChooser::emitPredicateMatch(raw_ostream &o, unsigned &Indentation,
                                        unsigned Opc) const {
   ListInit *Predicates =
     AllInstructions[Opc]->TheDef->getValueAsListInit("Predicates");
+  bool IsFirstEmission = true;
   for (unsigned i = 0; i < Predicates->getSize(); ++i) {
     Record *Pred = Predicates->getElementAsRecord(i);
     if (!Pred->getValue("AssemblerMatcherPredicate"))
@@ -1122,7 +1123,7 @@ bool FilterChooser::emitPredicateMatch(raw_ostream &o, unsigned &Indentation,
     if (!P.length())
       continue;
 
-    if (i != 0)
+    if (!IsFirstEmission)
       o << " && ";
 
     StringRef SR(P);
@@ -1133,6 +1134,7 @@ bool FilterChooser::emitPredicateMatch(raw_ostream &o, unsigned &Indentation,
       pairs = pairs.second.split(',');
     }
     emitSinglePredicateMatch(o, pairs.first, Emitter->PredicateNamespace);
+    IsFirstEmission = false;
   }
   return Predicates->getSize() > 0;
 }