[GISel] Explicitly disable BF16 tablegen patterns.

We currently have an issue where bf16 patters can be used to match fp16 types,
as GISel does not know about the difference between the two types. This patch
explicitly disables them to make sure that they are never used.

Author: davemgreen

llvm/test/CodeGen/AArch64/fptrunc.ll

@@ -1,6 +1,7 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 3
 ; RUN: llc -mtriple=aarch64 -global-isel=0 -verify-machineinstrs %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-SD
 ; RUN: llc -mtriple=aarch64 -global-isel=1 -verify-machineinstrs %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-GI
+; RUN: llc -mtriple=aarch64 -global-isel=1 -mattr=+fullfp16,+bf16 -verify-machineinstrs %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-GI
 
 define float @fptrunc_f64_f32(double %a) {
 ; CHECK-LABEL: fptrunc_f64_f32:

llvm/utils/TableGen/GlobalISelEmitter.cpp

@@ -2346,6 +2346,20 @@ void GlobalISelEmitter::emitRunCustomAction(raw_ostream &OS) {
      << "}\n";
 }
 
+bool hasBFloatType(const TreePatternNode &Node) {
+  for (unsigned I = 0, E = Node.getNumTypes(); I < E; I++) {
+    auto Ty = Node.getType(I);
+    for (auto T : Ty)
+      if (T.second == MVT::bf16 ||
+          (T.second.isVector() && T.second.getScalarType() == MVT::bf16))
+        return true;
+  }
+  for (const TreePatternNode &C : Node.children())
+    if (hasBFloatType(C))
+      return true;
+  return false;
+}
+
 void GlobalISelEmitter::run(raw_ostream &OS) {
   if (!UseCoverageFile.empty()) {
     RuleCoverage = CodeGenCoverage();
@@ -2382,6 +2396,13 @@ void GlobalISelEmitter::run(raw_ostream &OS) {
 
     if (Pat.getGISelShouldIgnore())
       continue; // skip without warning
+
+    // Skip any patterns containing BF16 types, as GISel cannot currently tell
+    // the difference between fp16 and bf16. FIXME: This can be removed once
+    // BF16 is supported properly.
+    if (hasBFloatType(Pat.getSrcPattern()))
+      continue;
+
     auto MatcherOrErr = runOnPattern(Pat);
 
     // The pattern analysis can fail, indicating an unsupported pattern.