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author | Owen Anderson <resistor@mac.com> | 2010-08-19 22:15:40 +0000 |
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committer | Owen Anderson <resistor@mac.com> | 2010-08-19 22:15:40 +0000 |
commit | 9419cab4c360d532bb5c3e171cdc8eca400b1b53 (patch) | |
tree | 4e9728bae3746d75963493388c7176a7f80a6273 | |
parent | b57326c8aab6f6089b29e324c39811d494d6fc42 (diff) | |
download | llvm-9419cab4c360d532bb5c3e171cdc8eca400b1b53.tar.gz llvm-9419cab4c360d532bb5c3e171cdc8eca400b1b53.tar.bz2 llvm-9419cab4c360d532bb5c3e171cdc8eca400b1b53.tar.xz |
When a set of bitmask operations, typically from a bitfield initialization, only modifies the low bytes of a value,
we can narrow the store to only over-write the affected bytes.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@111568 91177308-0d34-0410-b5e6-96231b3b80d8
-rw-r--r-- | lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp | 45 | ||||
-rw-r--r-- | test/Transforms/InstCombine/2010-08-19-StoreNarrowing.ll | 21 |
2 files changed, 66 insertions, 0 deletions
diff --git a/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp index b68fbc2db5..2f3d8b2b3e 100644 --- a/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp +++ b/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp @@ -14,11 +14,13 @@ #include "InstCombine.h" #include "llvm/IntrinsicInst.h" #include "llvm/Analysis/Loads.h" +#include "llvm/Support/PatternMatch.h" #include "llvm/Target/TargetData.h" #include "llvm/Transforms/Utils/BasicBlockUtils.h" #include "llvm/Transforms/Utils/Local.h" #include "llvm/ADT/Statistic.h" using namespace llvm; +using namespace PatternMatch; STATISTIC(NumDeadStore, "Number of dead stores eliminated"); @@ -473,6 +475,49 @@ Instruction *InstCombiner::visitStoreInst(StoreInst &SI) { if (SI.isVolatile()) return 0; // Don't hack volatile stores. + // Attempt to narrow sequences where we load a wide value, perform bitmasks + // that only affect the low bits of it, and then store it back. This + // typically arises from bitfield initializers in C++. + ConstantInt *CI1 =0, *CI2 = 0; + Value *Ld = 0; + if (getTargetData() && + match(SI.getValueOperand(), + m_And(m_Or(m_Value(Ld), m_ConstantInt(CI1)), m_ConstantInt(CI2))) && + isa<LoadInst>(Ld) && + equivalentAddressValues(cast<LoadInst>(Ld)->getPointerOperand(), Ptr)) { + APInt OrMask = CI1->getValue(); + APInt AndMask = CI2->getValue(); + + // Compute the prefix of the value that is unmodified by the bitmasking. + unsigned LeadingAndOnes = AndMask.countLeadingOnes(); + unsigned LeadingOrZeros = OrMask.countLeadingZeros(); + unsigned Prefix = std::min(LeadingAndOnes, LeadingOrZeros); + uint64_t NewWidth = AndMask.getBitWidth() - Prefix; + if (!isPowerOf2_64(NewWidth)) NewWidth = NextPowerOf2(NewWidth); + + // If we can find a power-of-2 prefix (and if the values we're working with + // are themselves POT widths), then we can narrow the store. We rely on + // later iterations of instcombine to propagate the demanded bits to narrow + // the other computations in the chain. + if (NewWidth < AndMask.getBitWidth() && + isPowerOf2_64(AndMask.getBitWidth())) { + const Type *NewType = IntegerType::get(Ptr->getContext(), NewWidth); + const Type *NewPtrType = PointerType::getUnqual(NewType); + + Value *NewVal = Builder->CreateTrunc(SI.getValueOperand(), NewType); + Value *NewPtr = Builder->CreateBitCast(Ptr, NewPtrType); + + // On big endian targets, we need to offset from the original pointer + // in order to store to the low-bit suffix. + if (getTargetData()->isBigEndian()) { + uint64_t GEPOffset = (AndMask.getBitWidth() - NewWidth) / 8; + NewPtr = Builder->CreateConstGEP1_64(NewPtr, GEPOffset); + } + + return new StoreInst(NewVal, NewPtr); + } + } + // store X, null -> turns into 'unreachable' in SimplifyCFG if (isa<ConstantPointerNull>(Ptr) && SI.getPointerAddressSpace() == 0) { if (!isa<UndefValue>(Val)) { diff --git a/test/Transforms/InstCombine/2010-08-19-StoreNarrowing.ll b/test/Transforms/InstCombine/2010-08-19-StoreNarrowing.ll new file mode 100644 index 0000000000..d4d528943f --- /dev/null +++ b/test/Transforms/InstCombine/2010-08-19-StoreNarrowing.ll @@ -0,0 +1,21 @@ +; RUN: opt -S -instcombine %s | not grep and +target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64" +target triple = "x86_64-apple-darwin10.0.0" + +%class.A = type { i8, [3 x i8] } + +define void @_ZN1AC2Ev(%class.A* %this) nounwind ssp align 2 { +entry: + %0 = bitcast %class.A* %this to i32* ; <i32*> [#uses=5] + %1 = load i32* %0, align 4 ; <i32> [#uses=1] + %2 = and i32 %1, -8 ; <i32> [#uses=2] + store i32 %2, i32* %0, align 4 + %3 = and i32 %2, -57 ; <i32> [#uses=1] + %4 = or i32 %3, 8 ; <i32> [#uses=2] + store i32 %4, i32* %0, align 4 + %5 = and i32 %4, -65 ; <i32> [#uses=2] + store i32 %5, i32* %0, align 4 + %6 = and i32 %5, -129 ; <i32> [#uses=1] + store i32 %6, i32* %0, align 4 + ret void +} |