| From c2ac925d6e1599f9c667a16196bd36888df02e1e Mon Sep 17 00:00:00 2001 |
| From: Vitaly Buka <vitalybuka@google.com> |
| Date: Fri, 12 Jul 2019 17:21:55 +0000 |
| Subject: [PATCH] CodeGet: Init 32bit pointers with 0xFFFFFFFF |
| |
| Summary: |
| Patch makes D63967 effective for 32bit platforms and improves pattern |
| initialization there. It cuts size of 32bit binary compiled with |
| -ftrivial-auto-var-init=pattern by 2% (3% with -Os). |
| |
| Binary size change on CTMark, (with -fuse-ld=lld -Wl,--icf=all, similar results with default linker options) |
| ``` |
| master patch diff |
| Os pattern 7.915580e+05 7.698424e+05 -0.028387 |
| O3 pattern 9.953688e+05 9.752952e+05 -0.019325 |
| ``` |
| |
| Zero vs Pattern on master |
| ``` |
| zero pattern diff |
| Os 7.689712e+05 7.915580e+05 0.031380 |
| O3 9.744796e+05 9.953688e+05 0.021133 |
| ``` |
| |
| Zero vs Pattern with the patch |
| ``` |
| zero pattern diff |
| Os 7.689712e+05 7.698424e+05 0.000789 |
| O3 9.744796e+05 9.752952e+05 0.000742 |
| ``` |
| |
| Reviewers: pcc, eugenis, glider, jfb |
| |
| Reviewed By: jfb |
| |
| Subscribers: hubert.reinterpretcast, dexonsmith, cfe-commits |
| |
| Tags: #clang |
| |
| Differential Revision: https://reviews.llvm.org/D64597 |
| |
| llvm-svn: 365921 |
| --- |
| clang/lib/CodeGen/PatternInit.cpp | 28 +++++++++---------------- |
| clang/test/CodeGenCXX/auto-var-init.cpp | 2 +- |
| 2 files changed, 11 insertions(+), 19 deletions(-) |
| |
| diff --git a/clang/lib/CodeGen/PatternInit.cpp b/clang/lib/CodeGen/PatternInit.cpp |
| index 7a1baf96cfd..3410c7f2153 100644 |
| --- a/clang/lib/CodeGen/PatternInit.cpp |
| +++ b/clang/lib/CodeGen/PatternInit.cpp |
| @@ -17,12 +17,13 @@ llvm::Constant *clang::CodeGen::initializationPatternFor(CodeGenModule &CGM, |
| // repeated byte-pattern which makes it easier to synthesize. We use it for |
| // pointers as well as integers so that aggregates are likely to be |
| // initialized with this repeated value. |
| - constexpr uint64_t LargeValue = 0xAAAAAAAAAAAAAAAAull; |
| // For 32-bit platforms it's a bit trickier because, across systems, only the |
| - // zero page can reasonably be expected to be unmapped, and even then we need |
| - // a very low address. We use a smaller value, and that value sadly doesn't |
| - // have a repeated byte-pattern. We don't use it for integers. |
| - constexpr uint32_t SmallValue = 0x000000AA; |
| + // zero page can reasonably be expected to be unmapped. We use max 0xFFFFFFFF |
| + // assuming that memory access will overlap into zero page. |
| + const uint64_t IntValue = |
| + CGM.getContext().getTargetInfo().getMaxPointerWidth() < 64 |
| + ? 0xFFFFFFFFFFFFFFFFull |
| + : 0xAAAAAAAAAAAAAAAAull; |
| // Floating-point values are initialized as NaNs because they propagate. Using |
| // a repeated byte pattern means that it will be easier to initialize |
| // all-floating-point aggregates and arrays with memset. Further, aggregates |
| @@ -36,27 +37,18 @@ llvm::Constant *clang::CodeGen::initializationPatternFor(CodeGenModule &CGM, |
| Ty->isVectorTy() ? Ty->getVectorElementType() : Ty) |
| ->getBitWidth(); |
| if (BitWidth <= 64) |
| - return llvm::ConstantInt::get(Ty, LargeValue); |
| + return llvm::ConstantInt::get(Ty, IntValue); |
| return llvm::ConstantInt::get( |
| - Ty, llvm::APInt::getSplat(BitWidth, llvm::APInt(64, LargeValue))); |
| + Ty, llvm::APInt::getSplat(BitWidth, llvm::APInt(64, IntValue))); |
| } |
| if (Ty->isPtrOrPtrVectorTy()) { |
| auto *PtrTy = cast<llvm::PointerType>( |
| Ty->isVectorTy() ? Ty->getVectorElementType() : Ty); |
| unsigned PtrWidth = CGM.getContext().getTargetInfo().getPointerWidth( |
| PtrTy->getAddressSpace()); |
| - llvm::Type *IntTy = llvm::IntegerType::get(CGM.getLLVMContext(), PtrWidth); |
| - uint64_t IntValue; |
| - switch (PtrWidth) { |
| - default: |
| + if (PtrWidth > 64) |
| llvm_unreachable("pattern initialization of unsupported pointer width"); |
| - case 64: |
| - IntValue = LargeValue; |
| - break; |
| - case 32: |
| - IntValue = SmallValue; |
| - break; |
| - } |
| + llvm::Type *IntTy = llvm::IntegerType::get(CGM.getLLVMContext(), PtrWidth); |
| auto *Int = llvm::ConstantInt::get(IntTy, IntValue); |
| return llvm::ConstantExpr::getIntToPtr(Int, PtrTy); |
| } |
| |