Fix instcombine to obey requested alignment when merging allocas.

llvm-svn: 164117

1 files changed, 7 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index 6ecb4c52c40..5b6cf4a4a83 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -246,12 +246,16 @@ Instruction *InstCombiner::visitAllocaInst(AllocaInst &AI) {
           return &AI;
         }
 
+        // If the alignment of the entry block alloca is 0 (unspecified),
+        // assign it the preferred alignment.
+        if (EntryAI->getAlignment() == 0)
+          EntryAI->setAlignment(
+            TD->getPrefTypeAlignment(EntryAI->getAllocatedType()));
         // Replace this zero-sized alloca with the one at the start of the entry
         // block after ensuring that the address will be aligned enough for both
         // types.
-        unsigned MaxAlign =
-          std::max(TD->getPrefTypeAlignment(EntryAI->getAllocatedType()),
-                   TD->getPrefTypeAlignment(AI.getAllocatedType()));
+        unsigned MaxAlign = std::max(EntryAI->getAlignment(),
+                                     AI.getAlignment());
         EntryAI->setAlignment(MaxAlign);
         if (AI.getType() != EntryAI->getType())
           return new BitCastInst(EntryAI, AI.getType());