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Add support for elimination of load instruction from global constants

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@6912 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2003-06-26 05:06:25 +00:00
parent b75e1e79d7
commit 833b8a4181
1 changed files with 48 additions and 0 deletions

48
lib/Transforms/Scalar/InstructionCombining.cpp

@ -22,6 +22,7 @@
#include "llvm/Constants.h"
#include "llvm/ConstantHandling.h"
#include "llvm/DerivedTypes.h"
#include "llvm/GlobalVariable.h"
#include "llvm/Support/InstIterator.h"
#include "llvm/Support/InstVisitor.h"
#include "llvm/Support/CallSite.h"
@ -79,6 +80,7 @@ namespace {
Instruction *visitPHINode(PHINode &PN);
Instruction *visitGetElementPtrInst(GetElementPtrInst &GEP);
Instruction *visitAllocationInst(AllocationInst &AI);
Instruction *visitLoadInst(LoadInst &LI);
Instruction *visitBranchInst(BranchInst &BI);
// visitInstruction - Specify what to return for unhandled instructions...
@ -1261,6 +1263,52 @@ Instruction *InstCombiner::visitAllocationInst(AllocationInst &AI) {
return 0;
}
/// GetGEPGlobalInitializer - Given a constant, and a getelementptr
/// constantexpr, return the constant value being addressed by the constant
/// expression, or null if something is funny.
///
static Constant *GetGEPGlobalInitializer(Constant *C, ConstantExpr *CE) {
if (CE->getOperand(1) != Constant::getNullValue(Type::LongTy))
return 0; // Do not allow stepping over the value!
// Loop over all of the operands, tracking down which value we are
// addressing...
for (unsigned i = 2, e = CE->getNumOperands(); i != e; ++i)
if (ConstantUInt *CU = dyn_cast<ConstantUInt>(CE->getOperand(i))) {
ConstantStruct *CS = cast<ConstantStruct>(C);
if (CU->getValue() >= CS->getValues().size()) return 0;
C = cast<Constant>(CS->getValues()[CU->getValue()]);
} else if (ConstantSInt *CS = dyn_cast<ConstantSInt>(CE->getOperand(i))) {
ConstantArray *CA = cast<ConstantArray>(C);
if ((uint64_t)CS->getValue() >= CA->getValues().size()) return 0;
C = cast<Constant>(CA->getValues()[CS->getValue()]);
} else
return 0;
return C;
}
Instruction *InstCombiner::visitLoadInst(LoadInst &LI) {
Value *Op = LI.getOperand(0);
if (ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(Op))
Op = CPR->getValue();
// Instcombine load (constant global) into the value loaded...
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Op))
if (GV->isConstant())
return ReplaceInstUsesWith(LI, GV->getInitializer());
// Instcombine load (constantexpr_GEP global, 0, ...) into the value loaded...
if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Op))
if (CE->getOpcode() == Instruction::GetElementPtr)
if (ConstantPointerRef *G=dyn_cast<ConstantPointerRef>(CE->getOperand(0)))
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(G->getValue()))
if (GV->isConstant())
if (Constant *V = GetGEPGlobalInitializer(GV->getInitializer(), CE))
return ReplaceInstUsesWith(LI, V);
return 0;
}
Instruction *InstCombiner::visitBranchInst(BranchInst &BI) {
// Change br (not X), label True, label False to: br X, label False, True
if (BI.isConditional() && !isa<Constant>(BI.getCondition()))