GlobalOpt: If we have an inbounds GEP from a ConstantAggregateZero global that we just determined to be constant, replace all loads from it with a zero value.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153576 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/IPO/GlobalOpt.cpp b/lib/Transforms/IPO/GlobalOpt.cpp
index a32e550..1522aa4 100644
--- a/lib/Transforms/IPO/GlobalOpt.cpp
+++ b/lib/Transforms/IPO/GlobalOpt.cpp
@@ -341,6 +341,12 @@
dyn_cast_or_null<ConstantExpr>(ConstantFoldInstruction(GEP, TD, TLI));
if (Init && CE && CE->getOpcode() == Instruction::GetElementPtr)
SubInit = ConstantFoldLoadThroughGEPConstantExpr(Init, CE);
+
+ // If the initializer is an all-null value and we have an inbounds GEP,
+ // we already know what the result of any load from that GEP is.
+ // TODO: Handle splats.
+ if (Init && isa<ConstantAggregateZero>(Init) && GEP->isInBounds())
+ SubInit = Constant::getNullValue(GEP->getType()->getElementType());
}
Changed |= CleanupConstantGlobalUsers(GEP, SubInit, TD, TLI);