add a long-overdue AllocaInst::isStaticAlloca method.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@60080 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 12 insertions, 0 deletions

diff --git a/lib/VMCore/Instructions.cpp b/lib/VMCore/Instructions.cpp
index 66caf5f..5b271d6 100644
--- a/lib/VMCore/Instructions.cpp
+++ b/lib/VMCore/Instructions.cpp
@@ -732,6 +732,18 @@ AllocaInst::AllocaInst(const AllocaInst &AI)
                    Instruction::Alloca, AI.getAlignment()) {
 }
 
+/// isStaticAlloca - Return true if this alloca is in the entry block of the
+/// function and is a constant size.  If so, the code generator will fold it
+/// into the prolog/epilog code, so it is basically free.
+bool AllocaInst::isStaticAlloca() const {
+  // Must be constant size.
+  if (!isa<ConstantInt>(getArraySize())) return false;
+  
+  // Must be in the entry block.
+  const BasicBlock *Parent = getParent();
+  return Parent == &Parent->getParent()->front();
+}
+
 MallocInst::MallocInst(const MallocInst &MI)
   : AllocationInst(MI.getType()->getElementType(), (Value*)MI.getOperand(0),
                    Instruction::Malloc, MI.getAlignment()) {