PR21101: tablegen's FastISel emitter should filter out unused functions.

FastISel has a fixed set of virtual functions that are overridden by the
tablegen-generated code for each target. These functions are distinguished by
the kinds of operands, e.g., register + immediate = "ri". The FastISel emitter
has been blindly emitting functions with different combinations of operand
kinds, even for combinations that are completely unused by FastISel, e.g.,
"fastEmit_rrr". Change to filter out functions that will be irrelevant for
FastISel and do not bother generating the code for them. Also add explicit
"override" keywords for the virtual functions that are overridden.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218838 91177308-0d34-0410-b5e6-96231b3b80d8

utils/TableGen/FastISelEmitter.cpp

@@ -19,6 +19,7 @@
 
 #include "CodeGenDAGPatterns.h"
 #include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/StringSwitch.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/TableGen/Error.h"
@@ -541,6 +542,17 @@ void FastISelMap::collectPatterns(CodeGenDAGPatterns &CGP) {
         continue;
     }
 
+    // Check if the operands match one of the patterns handled by FastISel.
+    std::string ManglingSuffix;
+    raw_string_ostream SuffixOS(ManglingSuffix);
+    Operands.PrintManglingSuffix(SuffixOS, ImmediatePredicates, true);
+    SuffixOS.flush();
+    if (!StringSwitch<bool>(ManglingSuffix)
+        .Cases("", "r", "rr", "ri", "rf", true)
+        .Cases("rri", "i", "f", true)
+        .Default(false))
+      continue;
+
     // Get the predicate that guards this pattern.
     std::string PredicateCheck = Pattern.getPredicateCheck();
 
@@ -803,7 +815,10 @@ void FastISelMap::printFunctionDefinitions(raw_ostream &OS) {
     if (!Operands.empty())
       OS << ", ";
     Operands.PrintParameters(OS);
-    OS << ") {\n";
+    OS << ") ";
+    if (!Operands.hasAnyImmediateCodes())
+      OS << "override ";
+    OS << "{\n";
 
     // If there are any forms of this signature available that operate on
     // constrained forms of the immediate (e.g., 32-bit sext immediate in a