Check result of emitStrLen before passing it to CreateGEP

Summary:
This fixes PR43081, where the transformation of `strchr(p, 0) -> p +
strlen(p)` can cause a segfault, if `-fno-builtin-strlen` is used.  In
that case, `emitStrLen` returns nullptr, which CreateGEP is not designed
to handle.  Also add the minimized code from the PR as a test case.

Reviewers: xbolva00, spatel, jdoerfert, efriedma

Reviewed By: efriedma

Subscribers: lebedev.ri, hiraditya, cfe-commits, llvm-commits

Tags: #clang, #llvm

Differential Revision: https://reviews.llvm.org/D70143

1 files changed, 2 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
index 0324993a820..18a17119b47 100644
--- a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -364,8 +364,8 @@ Value *LibCallSimplifier::optimizeStrChr(CallInst *CI, IRBuilder<> &B) {
   StringRef Str;
   if (!getConstantStringInfo(SrcStr, Str)) {
     if (CharC->isZero()) // strchr(p, 0) -> p + strlen(p)
-      return B.CreateGEP(B.getInt8Ty(), SrcStr, emitStrLen(SrcStr, B, DL, TLI),
-                         "strchr");
+      if (Value *StrLen = emitStrLen(SrcStr, B, DL, TLI))
+        return B.CreateGEP(B.getInt8Ty(), SrcStr, StrLen, "strchr");
     return nullptr;
   }