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constant fold loads from memcpy's from global constants. This is important
because clang lowers nontrivial automatic struct/array inits to memcpy from a global array. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@90698 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -31,8 +31,9 @@
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Analysis/Dominators.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/ConstantFolding.h"
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#include "llvm/Analysis/Dominators.h"
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#include "llvm/Analysis/MemoryBuiltins.h"
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#include "llvm/Analysis/MemoryDependenceAnalysis.h"
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#include "llvm/Support/CFG.h"
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@ -1094,11 +1095,39 @@ static int AnalyzeLoadFromClobberingMemInst(LoadInst *L, MemIntrinsic *MI,
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ConstantInt *SizeCst = dyn_cast<ConstantInt>(MI->getLength());
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if (SizeCst == 0) return -1;
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uint64_t MemSizeInBits = SizeCst->getZExtValue()*8;
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// If this is memset, we just need to see if the offset is valid in the size
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// of the memset..
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if (MI->getIntrinsicID() == Intrinsic::memset)
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return AnalyzeLoadFromClobberingWrite(L, MI->getDest(), MemSizeInBits, TD);
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// Unhandled memcpy/memmove.
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// If we have a memcpy/memmove, the only case we can handle is if this is a
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// copy from constant memory. In that case, we can read directly from the
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// constant memory.
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MemTransferInst *MTI = cast<MemTransferInst>(MI);
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Constant *Src = dyn_cast<Constant>(MTI->getSource());
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if (Src == 0) return -1;
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GlobalVariable *GV = dyn_cast<GlobalVariable>(Src->getUnderlyingObject());
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if (GV == 0 || !GV->isConstant()) return -1;
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// See if the access is within the bounds of the transfer.
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int Offset =
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AnalyzeLoadFromClobberingWrite(L, MI->getDest(), MemSizeInBits, TD);
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if (Offset == -1)
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return Offset;
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// Otherwise, see if we can constant fold a load from the constant with the
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// offset applied as appropriate.
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Src = ConstantExpr::getBitCast(Src,
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llvm::Type::getInt8PtrTy(Src->getContext()));
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Constant *OffsetCst =
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ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
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Src = ConstantExpr::getGetElementPtr(Src, &OffsetCst, 1);
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Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(L->getType()));
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if (ConstantFoldLoadFromConstPtr(Src, &TD))
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return Offset;
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return -1;
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}
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@ -1182,9 +1211,20 @@ static Value *GetMemInstValueForLoad(MemIntrinsic *SrcInst, unsigned Offset,
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return CoerceAvailableValueToLoadType(Val, LoadTy, InsertPt, TD);
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}
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// ABORT;
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return 0;
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// Otherwise, this is a memcpy/memmove from a constant global.
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MemTransferInst *MTI = cast<MemTransferInst>(SrcInst);
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Constant *Src = cast<Constant>(MTI->getSource());
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// Otherwise, see if we can constant fold a load from the constant with the
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// offset applied as appropriate.
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Src = ConstantExpr::getBitCast(Src,
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llvm::Type::getInt8PtrTy(Src->getContext()));
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Constant *OffsetCst =
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ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset);
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Src = ConstantExpr::getGetElementPtr(Src, &OffsetCst, 1);
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Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy));
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return ConstantFoldLoadFromConstPtr(Src, &TD);
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}
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@ -187,8 +187,24 @@ Cont:
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; CHECK: ret i16 %A
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}
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@GCst = constant {i32, float, i32 } { i32 42, float 14., i32 97 }
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; memset -> float forwarding.
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define float @memcpy_to_float_local(float* %A) nounwind ssp {
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entry:
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%conv = bitcast float* %A to i8* ; <i8*> [#uses=1]
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tail call void @llvm.memcpy.i64(i8* %conv, i8* bitcast ({i32, float, i32 }* @GCst to i8*), i64 12, i32 1)
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%arrayidx = getelementptr inbounds float* %A, i64 1 ; <float*> [#uses=1]
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%tmp2 = load float* %arrayidx ; <float> [#uses=1]
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ret float %tmp2
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; CHECK: @memcpy_to_float_local
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; CHECK-NOT: load
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; CHECK: ret float 1.400000e+01
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}
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declare void @llvm.memset.i64(i8* nocapture, i8, i64, i32) nounwind
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declare void @llvm.memcpy.i64(i8* nocapture, i8* nocapture, i64, i32) nounwind
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