TableGen: AsmMatcher missing-features list minimization.

When returning a 'cannot match due to missing CPU features' error code,
if there are multiple potential matches with different feature sets,
return the smallest set of missing features from the alternatives as
that's most likely to be the one that's desired.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158673 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 9 insertions, 3 deletions

diff --git a/utils/TableGen/AsmMatcherEmitter.cpp b/utils/TableGen/AsmMatcherEmitter.cpp
index e980b1a..f88e337 100644
--- a/utils/TableGen/AsmMatcherEmitter.cpp
+++ b/utils/TableGen/AsmMatcherEmitter.cpp
@@ -2575,6 +2575,7 @@ void AsmMatcherEmitter::run(raw_ostream &OS) {
   OS << "  bool HadMatchOtherThanFeatures = false;\n";
   OS << "  bool HadMatchOtherThanPredicate = false;\n";
   OS << "  unsigned RetCode = Match_InvalidOperand;\n";
+  OS << "  unsigned MissingFeatures = ~0U;\n";
   OS << "  // Set ErrorInfo to the operand that mismatches if it is\n";
   OS << "  // wrong for all instances of the instruction.\n";
   OS << "  ErrorInfo = ~0U;\n";
@@ -2622,7 +2623,11 @@ void AsmMatcherEmitter::run(raw_ostream &OS) {
   OS << "    if ((AvailableFeatures & it->RequiredFeatures) "
      << "!= it->RequiredFeatures) {\n";
   OS << "      HadMatchOtherThanFeatures = true;\n";
-  OS << "      ErrorInfo = it->RequiredFeatures & ~AvailableFeatures;\n";
+  OS << "      unsigned NewMissingFeatures = it->RequiredFeatures & "
+        "~AvailableFeatures;\n";
+  OS << "      if (CountPopulation_32(NewMissingFeatures) <= "
+        "CountPopulation_32(MissingFeatures))\n";
+  OS << "        MissingFeatures = NewMissingFeatures;\n";
   OS << "      continue;\n";
   OS << "    }\n";
   OS << "\n";
@@ -2656,8 +2661,9 @@ void AsmMatcherEmitter::run(raw_ostream &OS) {
 
   OS << "  // Okay, we had no match.  Try to return a useful error code.\n";
   OS << "  if (HadMatchOtherThanPredicate || !HadMatchOtherThanFeatures)";
-  OS << " return RetCode;\n";
-  OS << "  assert(ErrorInfo && \"missing feature(s) but what?!\");";
+  OS << "  return RetCode;\n";
+  OS << "  // Missing feature matches return which features were missing\n";
+  OS << "  ErrorInfo = MissingFeatures;\n";
   OS << "  return Match_MissingFeature;\n";
   OS << "}\n\n";