From: Bob Wilson Date: Sat, 30 Jan 2010 04:42:39 +0000 (+0000) Subject: Check alignment of loads when deciding whether it is safe to execute them X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=49db68fba01722ca032dc5170f8248a9d25f0199;p=oota-llvm.git Check alignment of loads when deciding whether it is safe to execute them unconditionally. Besides checking the offset, also check that the underlying object is aligned as much as the load itself. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@94875 91177308-0d34-0410-b5e6-96231b3b80d8 --- diff --git a/include/llvm/Transforms/Utils/Local.h b/include/llvm/Transforms/Utils/Local.h index 321151802bf..bb91d805893 100644 --- a/include/llvm/Transforms/Utils/Local.h +++ b/include/llvm/Transforms/Utils/Local.h @@ -39,7 +39,7 @@ template class SmallVectorImpl; /// specified pointer, we do a quick local scan of the basic block containing /// ScanFrom, to determine if the address is already accessed. bool isSafeToLoadUnconditionally(Value *V, Instruction *ScanFrom, - const TargetData *TD = 0); + unsigned Align, const TargetData *TD = 0); //===----------------------------------------------------------------------===// // Local constant propagation. diff --git a/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp index 422ffd03a89..2d13298300d 100644 --- a/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp +++ b/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp @@ -200,14 +200,15 @@ Instruction *InstCombiner::visitLoadInst(LoadInst &LI) { // if (SelectInst *SI = dyn_cast(Op)) { // load (select (Cond, &V1, &V2)) --> select(Cond, load &V1, load &V2). - if (isSafeToLoadUnconditionally(SI->getOperand(1), SI, TD) && - isSafeToLoadUnconditionally(SI->getOperand(2), SI, TD)) { + unsigned Align = LI.getAlignment(); + if (isSafeToLoadUnconditionally(SI->getOperand(1), SI, Align, TD) && + isSafeToLoadUnconditionally(SI->getOperand(2), SI, Align, TD)) { LoadInst *V1 = Builder->CreateLoad(SI->getOperand(1), - SI->getOperand(1)->getName()+".val"); + SI->getOperand(1)->getName()+".val"); LoadInst *V2 = Builder->CreateLoad(SI->getOperand(2), - SI->getOperand(2)->getName()+".val"); - V1->setAlignment(LI.getAlignment()); - V2->setAlignment(LI.getAlignment()); + SI->getOperand(2)->getName()+".val"); + V1->setAlignment(Align); + V2->setAlignment(Align); return SelectInst::Create(SI->getCondition(), V1, V2); } diff --git a/lib/Transforms/Scalar/GVN.cpp b/lib/Transforms/Scalar/GVN.cpp index 9c184526650..6e709523af3 100644 --- a/lib/Transforms/Scalar/GVN.cpp +++ b/lib/Transforms/Scalar/GVN.cpp @@ -1651,7 +1651,8 @@ bool GVN::processNonLocalLoad(LoadInst *LI, if (!allSingleSucc && // FIXME: REEVALUTE THIS. !isSafeToLoadUnconditionally(LoadPtr, - UnavailablePred->getTerminator(), TD)) { + UnavailablePred->getTerminator(), + LI->getAlignment(), TD)) { assert(NewInsts.empty() && "Should not have inserted instructions"); return false; } diff --git a/lib/Transforms/Scalar/TailRecursionElimination.cpp b/lib/Transforms/Scalar/TailRecursionElimination.cpp index 4119cb9db41..162d902cfa4 100644 --- a/lib/Transforms/Scalar/TailRecursionElimination.cpp +++ b/lib/Transforms/Scalar/TailRecursionElimination.cpp @@ -211,7 +211,8 @@ bool TailCallElim::CanMoveAboveCall(Instruction *I, CallInst *CI) { // FIXME: Writes to memory only matter if they may alias the pointer // being loaded from. if (CI->mayWriteToMemory() || - !isSafeToLoadUnconditionally(L->getPointerOperand(), L)) + !isSafeToLoadUnconditionally(L->getPointerOperand(), L, + L->getAlignment())) return false; } } diff --git a/lib/Transforms/Utils/Local.cpp b/lib/Transforms/Utils/Local.cpp index 425f5572969..62c0ae0d844 100644 --- a/lib/Transforms/Utils/Local.cpp +++ b/lib/Transforms/Utils/Local.cpp @@ -75,31 +75,38 @@ static Value *getUnderlyingObjectWithOffset(Value *V, const TargetData *TD, /// specified pointer, we do a quick local scan of the basic block containing /// ScanFrom, to determine if the address is already accessed. bool llvm::isSafeToLoadUnconditionally(Value *V, Instruction *ScanFrom, - const TargetData *TD) { + unsigned Align, const TargetData *TD) { uint64_t ByteOffset = 0; Value *Base = V; if (TD) Base = getUnderlyingObjectWithOffset(V, TD, ByteOffset); const Type *BaseType = 0; - if (const AllocaInst *AI = dyn_cast(Base)) - // If it is an alloca it is always safe to load from. + unsigned BaseAlign = 0; + if (const AllocaInst *AI = dyn_cast(Base)) { + // An alloca is safe to load from as load as it is suitably aligned. BaseType = AI->getAllocatedType(); - else if (const GlobalValue *GV = dyn_cast(Base)) { + BaseAlign = AI->getAlignment(); + } else if (const GlobalValue *GV = dyn_cast(Base)) { // Global variables are safe to load from but their size cannot be // guaranteed if they are overridden. - if (!isa(GV) && !GV->mayBeOverridden()) + if (!isa(GV) && !GV->mayBeOverridden()) { BaseType = GV->getType()->getElementType(); + BaseAlign = GV->getAlignment(); + } } + if (TD && BaseType && BaseAlign == 0) + BaseAlign = TD->getPrefTypeAlignment(BaseType); - if (BaseType) { + if (BaseType && Align <= BaseAlign) { if (!TD) return true; // Loading directly from an alloca or global is OK. if (BaseType->isSized()) { // Check if the load is within the bounds of the underlying object. const PointerType *AddrTy = cast(V->getType()); uint64_t LoadSize = TD->getTypeStoreSize(AddrTy->getElementType()); - if (ByteOffset + LoadSize <= TD->getTypeAllocSize(BaseType)) + if (ByteOffset + LoadSize <= TD->getTypeAllocSize(BaseType) && + (Align == 0 || (ByteOffset % Align) == 0)) return true; } } diff --git a/test/Transforms/GVN/load-pre-align.ll b/test/Transforms/GVN/load-pre-align.ll new file mode 100644 index 00000000000..3a66c0ba62f --- /dev/null +++ b/test/Transforms/GVN/load-pre-align.ll @@ -0,0 +1,44 @@ +; RUN: opt < %s -gvn -S | FileCheck %s + +target datalayout = "e-p:32:32:32-i1:8:32-i8:8:32-i16:16:32-i32:32:32-i64:32:32-f32:32:32-f64:32:32-v64:64:64-v128:128:128-a0:0:32-n32" + +@p = external global i32 + +define arm_apcscc i32 @test(i32 %n) nounwind { +; CHECK: @test +entry: + br label %for.cond + +; loads aligned greater than the memory should not be moved past conditionals +; CHECK-NOT: load +; CHECK: br i1 + +for.cond: + %i.0 = phi i32 [ 0, %entry ], [ %indvar.next, %for.inc ] + %cmp = icmp slt i32 %i.0, %n + br i1 %cmp, label %for.body, label %for.cond.for.end_crit_edge + +for.cond.for.end_crit_edge: +; ...but PRE can still move the load out of for.end to here. +; CHECK: for.cond.for.end_crit_edge: +; CHECK-NEXT: load + br label %for.end + +for.body: + %tmp3 = load i32* @p, align 8 + %dec = add i32 %tmp3, -1 + store i32 %dec, i32* @p + %cmp6 = icmp slt i32 %dec, 0 + br i1 %cmp6, label %for.body.for.end_crit_edge, label %for.inc + +for.body.for.end_crit_edge: + br label %for.end + +for.inc: + %indvar.next = add i32 %i.0, 1 + br label %for.cond + +for.end: + %tmp9 = load i32* @p, align 8 + ret i32 %tmp9 +}