[clang] 51717c9 - [dataflow] Avoid copying environment

[Sam McCall via cfe-commits]

Author: Sam McCall
Date: 2023-06-22T21:08:57+02:00
New Revision: 51717c93e74936a7d22f262b8c5f63efae3f8d11

URL: https://github.com/llvm/llvm-project/commit/51717c93e74936a7d22f262b8c5f63efae3f8d11
DIFF: https://github.com/llvm/llvm-project/commit/51717c93e74936a7d22f262b8c5f63efae3f8d11.diff

LOG: [dataflow] Avoid copying environment

This appears to be just an accidental copy rather than move from a scratch
variable.
As well as doing redundant work, these copies introduce extra SAT variables
which make debugging harder (each Enviroment has a unique FC token).

Example flow condition before:
```
(B0:1 = V15)
(B1:1 = V8)
(B2:1 = V10)
(B3:1 = (V4 & (!V7 => V6)))
(V10 = (B3:1 & !V7))
(V12 = B1:1)
(V13 = B2:1)
(V15 = (V12 | V13))
(V3 = V2)
(V4 = V3)
(V8 = (B3:1 & !!V7))
B0:1
V2
```

after:
```
(B0:1 = (V9 | V10))
(B1:1 = (B3:1 & !!V6))
(B2:1 = (B3:1 & !V6))
(B3:1 = (V3 & (!V6 => V5)))
(V10 = B2:1)
(V3 = V2)
(V9 = B1:1)
B0:1
V2
```

(with labelling from D153488)

There are also some more copies that can be avoided here (when multiple blocks
without terminating statements are joined), but they're less trivial, so I'll
put those in another patch.

Differential Revision: https://reviews.llvm.org/D153491

Added: 
    

Modified: 
    clang/lib/Analysis/FlowSensitive/TypeErasedDataflowAnalysis.cpp

Removed: 
    


################################################################################
diff  --git a/clang/lib/Analysis/FlowSensitive/TypeErasedDataflowAnalysis.cpp b/clang/lib/Analysis/FlowSensitive/TypeErasedDataflowAnalysis.cpp
index 37dd7081ae986..38853c4d75429 100644
--- a/clang/lib/Analysis/FlowSensitive/TypeErasedDataflowAnalysis.cpp
+++ b/clang/lib/Analysis/FlowSensitive/TypeErasedDataflowAnalysis.cpp
@@ -269,7 +269,7 @@ computeBlockInputState(const CFGBlock &Block, AnalysisContext &AC) {
     // initialize the state of each basic block 
diff erently.
     MaybeState.emplace(Analysis.typeErasedInitialElement(), AC.InitEnv);
   }
-  return *MaybeState;
+  return std::move(*MaybeState);
 }
 
 /// Built-in transfer function for `CFGStmt`.