[llvm] [MIRSampleProfile] Check nullptr Reader to avoid crash when profile file missing (PR #190186)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-pgo

Author: Frank515 (frank-515)

<details>
<summary>Changes</summary>

Fixes #<!-- -->189764

When the profile sample use file is not found, Reader is nullptr and causes a crash in MIRProfileLoader::runOnFunction.
This patch adds a null check at the beginning of the function to avoid the nullptr dereference.

---
Full diff: https://github.com/llvm/llvm-project/pull/190186.diff


1 Files Affected:

- (modified) llvm/lib/CodeGen/MIRSampleProfile.cpp (+2) 


``````````diff
diff --git a/llvm/lib/CodeGen/MIRSampleProfile.cpp b/llvm/lib/CodeGen/MIRSampleProfile.cpp
index 1f00446465c12..e2b31f9afb46d 100644
--- a/llvm/lib/CodeGen/MIRSampleProfile.cpp
+++ b/llvm/lib/CodeGen/MIRSampleProfile.cpp
@@ -317,6 +317,8 @@ bool MIRProfileLoader::runOnFunction(MachineFunction &MF) {
   // discriminator would end up getting zero samples. This could in turn undo
   // the sample distribution effort done by previous BFI maintenance and the
   // probe distribution factor work for pseudo probes.
+  if (!Reader)
+    return false;
   if (!Reader->profileIsFS())
     return false;
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/190186