[PATCH] D151606: [NFC][CLANG] Fix Static Code Analyzer Concerns with bad bit right shift operation in getNVPTXLaneID()

[Soumi Manna via Phabricator via cfe-commits]

Manna created this revision.
Manna added a reviewer: tahonermann.
Herald added subscribers: mattd, gchakrabarti, asavonic, manas, ASDenysPetrov, 
dkrupp, donat.nagy, Szelethus, a.sidorin, baloghadamsoftware.
Herald added a project: All.
Manna requested review of this revision.
Herald added a project: clang.

In getNVPTXLaneID(CodeGenFunction &), the value of LaneIDBits is 4294967295 
since function call 
llvm::Log2_32(CGF->getTarget()->getGridValue().GV_Warp_Size) might return 
4294967295.

  unsigned LaneIDBits =
       llvm::Log2_32(CGF.getTarget().getGridValue().GV_Warp_Size);
  unsigned LaneIDMask = ~0u >> (32u - LaneIDBits); 
  
  `

The shift amount (32U - LaneIDBits) might be 33, So it has undefined behavior 
for right shifting by more than 31 bits.

This patch adds an assert to guard the LaneIDBits overflow issue with  
LaneIDMask value.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D151606

Files:
  clang/lib/CodeGen/CGOpenMPRuntimeGPU.cpp


Index: clang/lib/CodeGen/CGOpenMPRuntimeGPU.cpp
===================================================================
--- clang/lib/CodeGen/CGOpenMPRuntimeGPU.cpp
+++ clang/lib/CodeGen/CGOpenMPRuntimeGPU.cpp
@@ -528,6 +528,8 @@
   CGBuilderTy &Bld = CGF.Builder;
   unsigned LaneIDBits =
       llvm::Log2_32(CGF.getTarget().getGridValue().GV_Warp_Size);
+  assert((32U - LaneIDBits) <= 33 &&
+         "Invalid LaneIDBits size in NVPTX device.");
   unsigned LaneIDMask = ~0u >> (32u - LaneIDBits);
   auto &RT = static_cast<CGOpenMPRuntimeGPU &>(CGF.CGM.getOpenMPRuntime());
   return Bld.CreateAnd(RT.getGPUThreadID(CGF), Bld.getInt32(LaneIDMask),



Index: clang/lib/CodeGen/CGOpenMPRuntimeGPU.cpp
===================================================================
--- clang/lib/CodeGen/CGOpenMPRuntimeGPU.cpp
+++ clang/lib/CodeGen/CGOpenMPRuntimeGPU.cpp
@@ -528,6 +528,8 @@
   CGBuilderTy &Bld = CGF.Builder;
   unsigned LaneIDBits =
       llvm::Log2_32(CGF.getTarget().getGridValue().GV_Warp_Size);
+  assert((32U - LaneIDBits) <= 33 &&
+         "Invalid LaneIDBits size in NVPTX device.");
   unsigned LaneIDMask = ~0u >> (32u - LaneIDBits);
   auto &RT = static_cast<CGOpenMPRuntimeGPU &>(CGF.CGM.getOpenMPRuntime());
   return Bld.CreateAnd(RT.getGPUThreadID(CGF), Bld.getInt32(LaneIDMask),

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