[SROA] Reuse existing lifetime markers if possible

Summary:
If the underlying alloca did not change, we do not necessarily need new
lifetime markers. This patch adds a check and reuses the old ones if
possible.

Reviewers: reames, ssarda, t.p.northover, hfinkel

Subscribers: hiraditya, bollu, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D68900

llvm-svn: 374692

1 files changed, 8 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Scalar/SROA.cpp b/llvm/lib/Transforms/Scalar/SROA.cpp
index 4b816832c31..a36b3c50ea3 100644
--- a/llvm/lib/Transforms/Scalar/SROA.cpp
+++ b/llvm/lib/Transforms/Scalar/SROA.cpp
@@ -3072,6 +3072,13 @@ private:
     LLVM_DEBUG(dbgs() << "    original: " << II << "\n");
     assert(II.getArgOperand(1) == OldPtr);
 
+    bool EntireRange = (NewBeginOffset == NewAllocaBeginOffset &&
+                        NewEndOffset == NewAllocaEndOffset);
+
+    // If the new lifetime marker would not differ from the old, just keep it.
+    if (&OldAI == &NewAI && EntireRange)
+      return true;
+
     // Record this instruction for deletion.
     Pass.DeadInsts.insert(&II);
 
@@ -3082,8 +3089,7 @@ private:
     // promoted, but PromoteMemToReg doesn't handle that case.)
     // FIXME: Check whether the alloca is promotable before dropping the
     // lifetime intrinsics?
-    if (NewBeginOffset != NewAllocaBeginOffset ||
-        NewEndOffset != NewAllocaEndOffset)
+    if (!EntireRange)
       return true;
 
     ConstantInt *Size =