[PGO] Don't unconditionally request BBInfo in verifyFuncBFI() (#140804)

This breaks in the case where there are unreachable blocks after an
entry block with no successors, which don't have a `BBInfo`, causing
crashes.

`BBInfo` doesn't exist for unreachable blocks, see
https://reviews.llvm.org/D27280.

Fixes #135828.

Author: aeubanks

llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp

@@ -2086,10 +2086,12 @@ static void verifyFuncBFI(PGOUseFunc &Func, LoopInfo &LI,
 
   unsigned BBNum = 0, BBMisMatchNum = 0, NonZeroBBNum = 0;
   for (auto &BBI : F) {
-    uint64_t CountValue = 0;
-    uint64_t BFICountValue = 0;
+    PGOUseBBInfo *BBInfo = Func.findBBInfo(&BBI);
+    if (!BBInfo)
+      continue;
 
-    CountValue = Func.getBBInfo(&BBI).Count.value_or(CountValue);
+    uint64_t CountValue = BBInfo->Count.value_or(CountValue);
+    uint64_t BFICountValue = 0;
 
     BBNum++;
     if (CountValue)

llvm/test/Transforms/PGOProfile/unreachable_bb2.ll

@@ -0,0 +1,29 @@
+; RUN: split-file %s %t
+; RUN: llvm-profdata merge %t/a.proftext -o %t/a.profdata
+; RUN: opt < %t/a.ll -passes=pgo-instr-use -pgo-test-profile-file=%t/a.profdata -S | FileCheck %s
+
+;--- a.ll
+
+declare ptr @bar()
+
+; CHECK: define ptr @foo
+; Ensure the profile hash matches. If it doesn't we emit the "instr_prof_hash_mismatch" metadata.
+; CHECK-NOT: instr_prof_hash_mismatch
+define ptr @foo() {
+entry:
+  ret ptr null
+
+2:
+  ret ptr null
+}
+
+;--- a.proftext
+# IR level Instrumentation Flag
+:ir
+foo
+# Func Hash:
+742261418966908927
+# Num Counters:
+1
+# Counter Values:
+1