Move some constant folding logic for loads out of instcombine into
Analysis/ConstantFolding.cpp. This doesn't change the behavior of
instcombine but makes other clients of ConstantFoldInstruction
able to handle loads. This was partially extracted from Eli's patch
in PR3152.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@84836 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/ConstantFolding.cpp b/lib/Analysis/ConstantFolding.cpp
index 0ce1c24..da671c8 100644
--- a/lib/Analysis/ConstantFolding.cpp
+++ b/lib/Analysis/ConstantFolding.cpp
@@ -30,6 +30,7 @@
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
#include "llvm/Support/MathExtras.h"
+#include "llvm/GlobalVariable.h"
#include <cerrno>
#include <cmath>
using namespace llvm;
@@ -92,6 +93,37 @@
return false;
}
+/// ConstantFoldLoadFromConstPtr - Return the value that a load from C would
+/// produce if it is constant and determinable. If this is not determinable,
+/// return null.
+Constant *llvm::ConstantFoldLoadFromConstPtr(Constant *C,
+ const TargetData *TD) {
+ // First, try the easy cases:
+ if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C))
+ if (GV->isConstant() && GV->hasDefinitiveInitializer())
+ return GV->getInitializer();
+
+ if (ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) {
+ if (CE->getOpcode() == Instruction::GetElementPtr) {
+ if (GlobalVariable *GV = dyn_cast<GlobalVariable>(CE->getOperand(0)))
+ if (GV->isConstant() && GV->hasDefinitiveInitializer())
+ if (Constant *V =
+ ConstantFoldLoadThroughGEPConstantExpr(GV->getInitializer(), CE))
+ return V;
+ }
+ }
+
+ return 0;
+}
+
+static Constant *ConstantFoldLoadInst(const LoadInst *LI, const TargetData *TD){
+ if (LI->isVolatile()) return 0;
+
+ if (Constant *C = dyn_cast<Constant>(LI->getOperand(0)))
+ return ConstantFoldLoadFromConstPtr(C, TD);
+
+ return 0;
+}
/// SymbolicallyEvaluateBinop - One of Op0/Op1 is a constant expression.
/// Attempt to symbolically evaluate the result of a binary operator merging
@@ -380,6 +412,9 @@
Ops.data(), Ops.size(),
Context, TD);
+ if (const LoadInst *LI = dyn_cast<LoadInst>(I))
+ return ConstantFoldLoadInst(LI, TD);
+
return ConstantFoldInstOperands(I->getOpcode(), I->getType(),
Ops.data(), Ops.size(), Context, TD);
}