[Bitcode] Drop invalid branch_weight in BitcodeReader

Summary:
If bitcode reader gets an invalid branch weight, drop that from the
inputs. This allows us to read the broken modules we generated before
the verifier was able to catch this.

rdar://64870641

Reviewers: yrouban, t.p.northover, dexonsmith, arphaman, aprantl

Reviewed By: aprantl

Subscribers: aprantl, hiraditya, jkorous, ributzka, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D83699

1 files changed, 30 insertions, 0 deletions

diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
index 86b8f5c..2c7882b 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -5394,6 +5394,36 @@ Error BitcodeReader::materialize(GlobalValue *GV) {
     }
   }
 
+  // "Upgrade" older incorrect branch weights by dropping them.
+  for (auto &I : instructions(F)) {
+    if (auto *MD = I.getMetadata(LLVMContext::MD_prof)) {
+      if (MD->getOperand(0) != nullptr && isa<MDString>(MD->getOperand(0))) {
+        MDString *MDS = cast<MDString>(MD->getOperand(0));
+        StringRef ProfName = MDS->getString();
+        // Check consistency of !prof branch_weights metadata.
+        if (!ProfName.equals("branch_weights"))
+          continue;
+        unsigned ExpectedNumOperands = 0;
+        if (BranchInst *BI = dyn_cast<BranchInst>(&I))
+          ExpectedNumOperands = BI->getNumSuccessors();
+        else if (SwitchInst *SI = dyn_cast<SwitchInst>(&I))
+          ExpectedNumOperands = SI->getNumSuccessors();
+        else if (isa<CallInst>(&I))
+          ExpectedNumOperands = 1;
+        else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(&I))
+          ExpectedNumOperands = IBI->getNumDestinations();
+        else if (isa<SelectInst>(&I))
+          ExpectedNumOperands = 2;
+        else
+          continue; // ignore and continue.
+
+        // If branch weight doesn't match, just strip branch weight.
+        if (MD->getNumOperands() != 1 + ExpectedNumOperands)
+          I.setMetadata(LLVMContext::MD_prof, nullptr);
+      }
+    }
+  }
+
   // Look for functions that rely on old function attribute behavior.
   UpgradeFunctionAttributes(*F);