[TableGen] Avoid emitting a switch that only contains a default.

[topperc]

Addresses post commit feedback from #174471

[llvmbot]

@llvm/pr-subscribers-tablegen

@llvm/pr-subscribers-llvm-selectiondag

Author: Craig Topper (topperc)

Changes

Addresses post commit feedback from #174471

---

Full diff: https://github.com/llvm/llvm-project/pull/177391.diff

1 Files Affected:

• (modified) llvm/utils/TableGen/DAGISelMatcherEmitter.cpp (+16-12)

diff --git a/llvm/utils/TableGen/DAGISelMatcherEmitter.cpp b/llvm/utils/TableGen/DAGISelMatcherEmitter.cpp
index eaecccf215342..0ab19d686714f 100644
--- a/llvm/utils/TableGen/DAGISelMatcherEmitter.cpp
+++ b/llvm/utils/TableGen/DAGISelMatcherEmitter.cpp
@@ -1364,19 +1364,23 @@ void MatcherTableEmitter::EmitValueTypeFunction(raw_ostream &OS) {
 
   for (const auto &[VTs, Idx] : ValueTypeMap) {
     OS << "  case " << (Idx - 1) << ":\n";
-    OS << "    switch (HwMode) {\n";
-    if (!VTs.hasDefault())
-      OS << "    default:\n      return MVT();\n";
-    for (const auto [Mode, VT] : VTs) {
-      if (Mode == DefaultMode)
-        OS << "    default:\n";
-      else
-        OS << "    case " << Mode << ":\n";
-      OS << "      return " << getEnumName(VT) << ";\n";
-    }
+    if (VTs.isSimple()) {
+      OS << "    return " << getEnumName(VTs.getSimple()) << ";\n";
+    } else {
+      OS << "    switch (HwMode) {\n";
+      if (!VTs.hasDefault())
+        OS << "    default:\n      return MVT();\n";
+      for (const auto [Mode, VT] : VTs) {
+        if (Mode == DefaultMode)
+          OS << "    default:\n";
+        else
+          OS << "    case " << Mode << ":\n";
+        OS << "      return " << getEnumName(VT) << ";\n";
+      }
 
-    OS << "    }\n";
-    OS << "    break;\n";
+      OS << "    }\n";
+      OS << "    break;\n";
+    }
   }
 
   OS << "  }\n";

[arsenm]

Bad warning to have enabled on generated code but ok

[RKSimon]

LGTM - cheers!