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https://github.com/c64scene-ar/llvm-6502.git
synced 2025-04-22 15:39:28 +00:00
Improve GVN to be able to forward substitute a small load
from a piece of a large store when both are in the same block. This allows clang to compile the testcase in PR4216 to this code: _test_bitfield: movl 4(%esp), %eax movl %eax, %ecx andl $-65536, %ecx orl $32962, %eax andl $40186, %eax orl %ecx, %eax ret This is not ideal, but is a whole lot better than the code produced by llvm-gcc: _test_bitfield: movw $-32574, %ax orw 4(%esp), %ax andw $-25350, %ax movw %ax, 4(%esp) movw 7(%esp), %cx shlw $8, %cx movzbl 6(%esp), %edx orw %cx, %dx movzwl %dx, %ecx shll $16, %ecx movzwl %ax, %eax orl %ecx, %eax ret and dramatically better than that produced by gcc 4.2: _test_bitfield: pushl %ebx call L3 "L00000000001$pb": L3: popl %ebx movl 8(%esp), %eax leal 0(,%eax,4), %edx sarb $7, %dl movl %eax, %ecx andl $7168, %ecx andl $-7201, %ebx movzbl %dl, %edx andl $1, %edx sall $5, %edx orl %ecx, %ebx orl %edx, %ebx andl $24, %eax andl $-58336, %ebx orl %eax, %ebx orl $32962, %ebx movl %ebx, %eax popl %ebx ret git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@82439 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
parent
0c1f688954
commit
eed919b1ba
@ -23,6 +23,7 @@
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#include "llvm/Function.h"
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#include "llvm/IntrinsicInst.h"
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#include "llvm/LLVMContext.h"
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#include "llvm/Operator.h"
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#include "llvm/Value.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/DepthFirstIterator.h"
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@ -38,6 +39,7 @@
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/ErrorHandling.h"
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#include "llvm/Support/GetElementPtrTypeIterator.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Target/TargetData.h"
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#include "llvm/Transforms/Utils/BasicBlockUtils.h"
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@ -1341,6 +1343,153 @@ bool GVN::processNonLocalLoad(LoadInst *LI,
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return true;
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}
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/// GetBaseWithConstantOffset - Analyze the specified pointer to see if it can
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/// be expressed as a base pointer plus a constant offset. Return the base and
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/// offset to the caller.
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static Value *GetBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
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const TargetData *TD) {
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Operator *PtrOp = dyn_cast<Operator>(Ptr);
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if (PtrOp == 0) return Ptr;
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// Just look through bitcasts.
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if (PtrOp->getOpcode() == Instruction::BitCast)
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return GetBaseWithConstantOffset(PtrOp->getOperand(0), Offset, TD);
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// If this is a GEP with constant indices, we can look through it.
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GEPOperator *GEP = dyn_cast<GEPOperator>(PtrOp);
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if (GEP == 0 || !GEP->hasAllConstantIndices()) return Ptr;
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gep_type_iterator GTI = gep_type_begin(GEP);
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for (User::op_iterator I = GEP->idx_begin(), E = GEP->idx_end(); I != E;
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++I, ++GTI) {
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ConstantInt *OpC = cast<ConstantInt>(*I);
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if (OpC->isZero()) continue;
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// Handle a struct and array indices which add their offset to the pointer.
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if (const StructType *STy = dyn_cast<StructType>(*GTI)) {
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Offset += TD->getStructLayout(STy)->getElementOffset(OpC->getZExtValue());
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} else {
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uint64_t Size = TD->getTypeAllocSize(GTI.getIndexedType());
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Offset += OpC->getSExtValue()*Size;
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}
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}
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// Re-sign extend from the pointer size if needed to get overflow edge cases
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// right.
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unsigned PtrSize = TD->getPointerSizeInBits();
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if (PtrSize < 64)
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Offset = (Offset << (64-PtrSize)) >> (64-PtrSize);
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return GetBaseWithConstantOffset(GEP->getPointerOperand(), Offset, TD);
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}
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/// HandleLoadFromClobberingStore - This function is called when we have a
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/// memdep query of a load that ends up being a clobbering store. This means
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/// that the store *may* provide bits used by the load but we can't be sure
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/// because the pointers don't mustalias. Check this case to see if there is
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/// anything more we can do before we give up.
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static Value *HandleLoadFromClobberingStore(LoadInst *L, StoreInst *DepSI,
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const TargetData *TD) {
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int64_t StoreOffset = 0, LoadOffset = 0;
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Value *StoreBase =
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GetBaseWithConstantOffset(DepSI->getPointerOperand(), StoreOffset, TD);
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Value *LoadBase =
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GetBaseWithConstantOffset(L->getPointerOperand(), LoadOffset, TD);
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if (StoreBase != LoadBase)
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return 0;
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// If the load and store are to the exact same address, they should have been
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// a must alias. AA must have gotten confused.
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// FIXME: Study to see if/when this happens.
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if (LoadOffset == StoreOffset) {
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#if 0
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errs() << "STORE/LOAD DEP WITH COMMON POINTER MISSED:\n"
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<< "Base = " << *StoreBase << "\n"
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<< "Store Ptr = " << *DepSI->getPointerOperand() << "\n"
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<< "Store Offs = " << StoreOffset << " - " << *DepSI << "\n"
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<< "Load Ptr = " << *L->getPointerOperand() << "\n"
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<< "Load Offs = " << LoadOffset << " - " << *L << "\n\n";
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errs() << "'" << L->getParent()->getParent()->getName() << "'"
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<< *L->getParent();
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#endif
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return 0;
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}
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// If the load and store don't overlap at all, the store doesn't provide
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// anything to the load. In this case, they really don't alias at all, AA
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// must have gotten confused.
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// FIXME: Investigate cases where this bails out, e.g. rdar://7238614. Then
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// remove this check, as it is duplicated with what we have below.
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uint64_t StoreSize = TD->getTypeSizeInBits(DepSI->getOperand(0)->getType());
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uint64_t LoadSize = TD->getTypeSizeInBits(L->getType());
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if ((StoreSize & 7) | (LoadSize & 7))
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return 0;
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StoreSize >>= 3; // Convert to bytes.
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LoadSize >>= 3;
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bool isAAFailure = false;
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if (StoreOffset < LoadOffset) {
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isAAFailure = StoreOffset+int64_t(StoreSize) <= LoadOffset;
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} else {
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isAAFailure = LoadOffset+int64_t(LoadSize) <= StoreOffset;
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}
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if (isAAFailure) {
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#if 0
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errs() << "STORE LOAD DEP WITH COMMON BASE:\n"
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<< "Base = " << *StoreBase << "\n"
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<< "Store Ptr = " << *DepSI->getPointerOperand() << "\n"
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<< "Store Offs = " << StoreOffset << " - " << *DepSI << "\n"
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<< "Load Ptr = " << *L->getPointerOperand() << "\n"
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<< "Load Offs = " << LoadOffset << " - " << *L << "\n\n";
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errs() << "'" << L->getParent()->getParent()->getName() << "'"
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<< *L->getParent();
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#endif
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return 0;
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}
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// If the Load isn't completely contained within the stored bits, we don't
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// have all the bits to feed it. We could do something crazy in the future
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// (issue a smaller load then merge the bits in) but this seems unlikely to be
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// valuable.
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if (StoreOffset > LoadOffset ||
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StoreOffset+StoreSize < LoadOffset+LoadSize)
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return 0;
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// Adjust LoadOffset to be relative from the start of StoreOffset.
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LoadOffset -= StoreOffset;
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Value *SrcVal = DepSI->getOperand(0);
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LLVMContext &Ctx = SrcVal->getType()->getContext();
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// Compute which bits of the stored value are being used by the load. Convert
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// to an integer type to start with.
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if (isa<PointerType>(SrcVal->getType()))
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SrcVal = new PtrToIntInst(SrcVal, TD->getIntPtrType(Ctx), "tmp", L);
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if (!isa<IntegerType>(SrcVal->getType()))
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SrcVal = new BitCastInst(SrcVal, IntegerType::get(Ctx, StoreSize*8), "", L);
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// Shift the bits to the least significant depending on endianness.
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unsigned ShiftAmt;
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if (TD->isLittleEndian()) {
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ShiftAmt = LoadOffset*8;
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} else {
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ShiftAmt = StoreSize-LoadSize-LoadOffset;
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}
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SrcVal = BinaryOperator::CreateLShr(SrcVal,
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ConstantInt::get(SrcVal->getType(), ShiftAmt), "tmp", L);
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SrcVal = new TruncInst(SrcVal, IntegerType::get(Ctx, LoadSize*8), "", L);
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return CoerceAvailableValueToLoadType(SrcVal, L->getType(), L, *TD);
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}
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/// processLoad - Attempt to eliminate a load, first by eliminating it
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/// locally, and then attempting non-local elimination if that fails.
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bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) {
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@ -1352,7 +1501,12 @@ bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) {
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// If the value isn't available, don't do anything!
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if (Dep.isClobber()) {
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// FIXME: In the future, we should handle things like:
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// FIXME: We should handle memset/memcpy/memmove as dependent instructions
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// to forward the value if available.
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//if (isa<MemIntrinsic>(Dep.getInst()))
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//errs() << "LOAD DEPENDS ON MEM: " << *L << "\n" << *Dep.getInst()<<"\n\n";
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// Check to see if we have something like this:
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// store i32 123, i32* %P
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// %A = bitcast i32* %P to i8*
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// %B = gep i8* %A, i32 1
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@ -1362,6 +1516,21 @@ bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) {
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// a common base + constant offset, and if the previous store (or memset)
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// completely covers this load. This sort of thing can happen in bitfield
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// access code.
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if (StoreInst *DepSI = dyn_cast<StoreInst>(Dep.getInst()))
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if (const TargetData *TD = getAnalysisIfAvailable<TargetData>())
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if (Value *AvailVal = HandleLoadFromClobberingStore(L, DepSI, TD)) {
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DEBUG(errs() << "GVN COERCED STORE BITS:\n" << *DepSI << '\n'
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<< *AvailVal << '\n' << *L << "\n\n\n");
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// Replace the load!
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L->replaceAllUsesWith(AvailVal);
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if (isa<PointerType>(AvailVal->getType()))
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MD->invalidateCachedPointerInfo(AvailVal);
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toErase.push_back(L);
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NumGVNLoad++;
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return true;
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}
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DEBUG(
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// fast print dep, using operator<< on instruction would be too slow
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errs() << "GVN: load ";
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@ -1429,12 +1598,6 @@ bool GVN::processLoad(LoadInst *L, SmallVectorImpl<Instruction*> &toErase) {
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return true;
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}
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// FIXME: We should handle memset/memcpy/memmove as dependent instructions to
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// forward the value if available.
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//if (isa<MemIntrinsic>(DepInst))
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// errs() << "LOAD DEPENDS ON MEM: " << *L << "\n" << *DepInst << "\n\n";
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// If this load really doesn't depend on anything, then we must be loading an
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// undef value. This can happen when loading for a fresh allocation with no
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// intervening stores, for example.
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@ -141,6 +141,35 @@ Cont:
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; CHECK: ret i8 %A
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}
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;; non-local i32/float -> i8 load forwarding. This also tests that the "P3"
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;; bitcast equivalence can be properly phi translated.
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define i8 @coerce_mustalias_nonlocal1(i32* %P, i1 %cond) {
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%P2 = bitcast i32* %P to float*
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br i1 %cond, label %T, label %F
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T:
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store i32 42, i32* %P
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br label %Cont
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F:
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store float 1.0, float* %P2
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br label %Cont
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Cont:
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%P3 = bitcast i32* %P to i8*
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%A = load i8* %P3
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ret i8 %A
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;; FIXME: This is disabled because this caused a miscompile in the llvm-gcc
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;; bootstrap, see r82411
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;
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; HECK: @coerce_mustalias_nonlocal1
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; HECK: Cont:
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; HECK: %A = phi i8 [
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; HECK-NOT: load
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; HECK: ret i8 %A
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}
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;; non-local i32 -> i8 partial redundancy load forwarding.
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define i8 @coerce_mustalias_pre0(i32* %P, i1 %cond) {
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%P3 = bitcast i32* %P to i8*
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@ -165,3 +194,24 @@ Cont:
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; CHECK: ret i8 %A
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}
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;;===----------------------------------------------------------------------===;;
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;; Store -> Load and Load -> Load forwarding where src and dst are different
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;; types, and the reload is an offset from the store pointer.
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;;===----------------------------------------------------------------------===;;
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;; i32 -> f32 forwarding.
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define i8 @coerce_offset0(i32 %V, i32* %P) {
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store i32 %V, i32* %P
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%P2 = bitcast i32* %P to i8*
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%P3 = getelementptr i8* %P2, i32 2
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%A = load i8* %P3
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ret i8 %A
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; CHECK: @coerce_offset0
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; CHECK-NOT: load
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; CHECK: ret i8
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}
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