[Clang] Always verify LLVM IR inputs

We get a lot of issues that basically boil down to "I passed
malformed LLVM IR to clang and it crashed". Clang does not perform
IR verification by default in (non-assertion-enabled) release
builds, and that's sensible for IR that Clang itself produces,
which is expected to always be valid. However, if people pass in
their own handwritten IR, we should report if it is malformed,
instead of crashing. We should also report it in a way that does
not produce a crash trace and ask for a bug report, as currently
happens in assertions-enabled builds.

I've only added the verification for textual IR inputs. I don't
want to force verification for bitcode inputs, as these would
affect typical LTO scenarios, and are usually coming from Clang
itself.

Author: nikic

clang/include/clang/Basic/DiagnosticFrontendKinds.td

@@ -379,6 +379,8 @@ def err_ast_action_on_llvm_ir : Error<
   "cannot apply AST actions to LLVM IR file '%0'">,
   DefaultFatal;
 
+def err_invalid_llvm_ir : Error<"invalid LLVM IR input: %0">;
+
 def err_os_unsupport_riscv_fmv : Error<
   "function multiversioning is currently only supported on Linux">;
 

clang/lib/CodeGen/CodeGenAction.cpp

@@ -39,6 +39,7 @@
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/LLVMRemarkStreamer.h"
 #include "llvm/IR/Module.h"
+#include "llvm/IR/Verifier.h"
 #include "llvm/IRReader/IRReader.h"
 #include "llvm/LTO/LTOBackend.h"
 #include "llvm/Linker/Linker.h"
@@ -1048,8 +1049,20 @@ CodeGenAction::loadModule(MemoryBufferRef MBRef) {
 
   // Handle textual IR and bitcode file with one single module.
   llvm::SMDiagnostic Err;
-  if (std::unique_ptr<llvm::Module> M = parseIR(MBRef, Err, *VMContext))
+  if (std::unique_ptr<llvm::Module> M = parseIR(MBRef, Err, *VMContext)) {
+    // For textual LLVM IR files, always verify the input and report the error
+    // in a way that does not ask people to report an issue for it.
+    if (!llvm::isBitcode((const unsigned char *)MBRef.getBufferStart(),
+                         (const unsigned char *)MBRef.getBufferEnd())) {
+      std::string VerifierErr;
+      raw_string_ostream VerifierErrStream(VerifierErr);
+      if (llvm::verifyModule(*M, &VerifierErrStream)) {
+        CI.getDiagnostics().Report(diag::err_invalid_llvm_ir) << VerifierErr;
+        return {};
+      }
+    }
     return M;
+  }
 
   // If MBRef is a bitcode with multiple modules (e.g., -fsplit-lto-unit
   // output), place the extra modules (actually only one, a regular LTO module)

clang/test/CodeGen/invalid_llvm_ir.ll

@@ -0,0 +1,10 @@
+; RUN: not %clang %s 2>&1 | FileCheck %s
+
+; CHECK: error: invalid LLVM IR input: PHINode should have one entry for each predecessor of its parent basic block!
+; CHECK-NEXT: %phi = phi i32 [ 0, %entry ]
+
+define void @test() {
+entry:
+  %phi = phi i32 [ 0, %entry ]
+  ret void
+}