[llvm] a822ec7 - [DSE,MSSA] Treat passed by value args as invisible to caller.

[Florian Hahn via llvm-commits]

Author: Florian Hahn
Date: 2020-06-23T08:58:51+01:00
New Revision: a822ec75cc6044eae8dd99d1b78c1a7eb9ad40d7

URL: https://github.com/llvm/llvm-project/commit/a822ec75cc6044eae8dd99d1b78c1a7eb9ad40d7
DIFF: https://github.com/llvm/llvm-project/commit/a822ec75cc6044eae8dd99d1b78c1a7eb9ad40d7.diff

LOG: [DSE,MSSA] Treat passed by value args as invisible to caller.

This updates the MemorySSA backed implementation to treat arguments
passed by value similar to allocas: in they are assumed to be invisible
in the caller. This is similar to how they are treated in legacy DSE.

Reviewers: efriedma, asbirlea, george.burgess.iv

Reviewed By: efriedma

Differential Revision: https://reviews.llvm.org/D82222

Added: 
    

Modified: 
    llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp

Removed: 
    


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diff  --git a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
index c6f579b61746..469c8795e0ba 100644
--- a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
@@ -1563,8 +1563,13 @@ struct DSEState {
     // Treat byval or inalloca arguments the same as Allocas, stores to them are
     // dead at the end of the function.
     for (Argument &AI : F.args())
-      if (AI.hasPassPointeeByValueAttr())
-        State.InvisibleToCallerBeforeRet.insert(&AI);
+      if (AI.hasPassPointeeByValueAttr()) {
+        // For byval, the caller doesn't know the address of the allocation.
+        if (AI.hasByValAttr())
+          State.InvisibleToCallerBeforeRet.insert(&AI);
+        State.InvisibleToCallerAfterRet.insert(&AI);
+      }
+
     return State;
   }