From 8e16d73346f8091461319a7dfc4ddd18eedcff13 Mon Sep 17 00:00:00 2001 From: Clement Courbet Date: Fri, 8 Mar 2019 09:07:45 +0000 Subject: [PATCH] [SelectionDAG] Allow the user to specify a memeq function. Summary: Right now, when we encounter a string equality check, e.g. `if (memcmp(a, b, s) == 0)`, we try to expand to a comparison if `s` is a small compile-time constant, and fall back on calling `memcmp()` else. This is sub-optimal because memcmp has to compute much more than equality. This patch replaces `memcmp(a, b, s) == 0` by `bcmp(a, b, s) == 0` on platforms that support `bcmp`. `bcmp` can be made much more efficient than `memcmp` because equality compare is trivially parallel while lexicographic ordering has a chain dependency. Subscribers: fedor.sergeev, jyknight, ckennelly, gchatelet, llvm-commits Differential Revision: https://reviews.llvm.org/D56593 llvm-svn: 355672 --- llvm/docs/ReleaseNotes.rst | 5 ++ llvm/include/llvm/Transforms/Utils/BuildLibCalls.h | 4 ++ llvm/lib/Analysis/TargetLibraryInfo.cpp | 13 +++++ llvm/lib/Transforms/Utils/BuildLibCalls.cpp | 31 +++++++--- llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp | 41 ++++++++----- llvm/test/CodeGen/X86/memcmp.ll | 67 ++++++++++++++++++++++ .../test/Transforms/InferFunctionAttrs/annotate.ll | 9 ++- llvm/test/Transforms/InstCombine/memcmp-1.ll | 21 ++++++- llvm/test/Transforms/InstCombine/strcmp-1.ll | 24 +++++++- 9 files changed, 187 insertions(+), 28 deletions(-) diff --git a/llvm/docs/ReleaseNotes.rst b/llvm/docs/ReleaseNotes.rst index 52a8b11..ff116b6 100644 --- a/llvm/docs/ReleaseNotes.rst +++ b/llvm/docs/ReleaseNotes.rst @@ -40,6 +40,11 @@ Non-comprehensive list of changes in this release functionality, or simply have a lot to talk about), see the `NOTE` below for adding a new subsection. +* The optimizer will now convert calls to memcmp into a calls to bcmp in some + circumstances. Users who are building freestanding code (not depending on the + platform's libc) without specifying -ffreestanding may need to either pass + -fno-builtin-bcmp, or provide a bcmp function. + .. NOTE If you would like to document a larger change, then you can add a subsection about it right here. You can copy the following boilerplate diff --git a/llvm/include/llvm/Transforms/Utils/BuildLibCalls.h b/llvm/include/llvm/Transforms/Utils/BuildLibCalls.h index 6c61cbe..0c97f7d 100644 --- a/llvm/include/llvm/Transforms/Utils/BuildLibCalls.h +++ b/llvm/include/llvm/Transforms/Utils/BuildLibCalls.h @@ -92,6 +92,10 @@ namespace llvm { Value *emitMemCmp(Value *Ptr1, Value *Ptr2, Value *Len, IRBuilder<> &B, const DataLayout &DL, const TargetLibraryInfo *TLI); + /// Emit a call to the bcmp function. + Value *emitBCmp(Value *Ptr1, Value *Ptr2, Value *Len, IRBuilder<> &B, + const DataLayout &DL, const TargetLibraryInfo *TLI); + /// Emit a call to the unary function named 'Name' (e.g. 'floor'). This /// function is known to take a single of type matching 'Op' and returns one /// value with the same type. If 'Op' is a long double, 'l' is added as the diff --git a/llvm/lib/Analysis/TargetLibraryInfo.cpp b/llvm/lib/Analysis/TargetLibraryInfo.cpp index 29e460e..50a05a8 100644 --- a/llvm/lib/Analysis/TargetLibraryInfo.cpp +++ b/llvm/lib/Analysis/TargetLibraryInfo.cpp @@ -49,6 +49,16 @@ static bool hasSinCosPiStret(const Triple &T) { return true; } +static bool hasBcmp(const Triple &TT) { + // Posix removed support from bcmp() in 2001, but the glibc and several + // implementations of the libc still have it. + if (TT.isOSLinux()) + return TT.isGNUEnvironment() || TT.isMusl(); + // Both NetBSD and OpenBSD are planning to remove the function. Windows does + // not have it. + return TT.isOSFreeBSD() || TT.isOSSolaris() || TT.isOSDarwin(); +} + /// Initialize the set of available library functions based on the specified /// target triple. This should be carefully written so that a missing target /// triple gets a sane set of defaults. @@ -141,6 +151,9 @@ static void initialize(TargetLibraryInfoImpl &TLI, const Triple &T, TLI.setUnavailable(LibFunc_sincospif_stret); } + if (!hasBcmp(T)) + TLI.setUnavailable(LibFunc_bcmp); + if (T.isMacOSX() && T.getArch() == Triple::x86 && !T.isMacOSXVersionLT(10, 7)) { // x86-32 OSX has a scheme where fwrite and fputs (and some other functions diff --git a/llvm/lib/Transforms/Utils/BuildLibCalls.cpp b/llvm/lib/Transforms/Utils/BuildLibCalls.cpp index 5688508..fe6c602e 100644 --- a/llvm/lib/Transforms/Utils/BuildLibCalls.cpp +++ b/llvm/lib/Transforms/Utils/BuildLibCalls.cpp @@ -930,28 +930,41 @@ Value *llvm::emitMemChr(Value *Ptr, Value *Val, Value *Len, IRBuilder<> &B, return CI; } -Value *llvm::emitMemCmp(Value *Ptr1, Value *Ptr2, Value *Len, IRBuilder<> &B, - const DataLayout &DL, const TargetLibraryInfo *TLI) { - if (!TLI->has(LibFunc_memcmp)) +// Common code for memcmp() and bcmp(), which have the exact same properties, +// just a slight difference in semantics. +static Value *emitMemCmpOrBcmp(llvm::LibFunc libfunc, Value *Ptr1, Value *Ptr2, + Value *Len, IRBuilder<> &B, const DataLayout &DL, + const TargetLibraryInfo *TLI) { + if (!TLI->has(libfunc)) return nullptr; Module *M = B.GetInsertBlock()->getModule(); - StringRef MemCmpName = TLI->getName(LibFunc_memcmp); + StringRef CmpFnName = TLI->getName(libfunc); LLVMContext &Context = B.GetInsertBlock()->getContext(); - FunctionCallee MemCmp = - M->getOrInsertFunction(MemCmpName, B.getInt32Ty(), B.getInt8PtrTy(), + FunctionCallee CmpFn = + M->getOrInsertFunction(CmpFnName, B.getInt32Ty(), B.getInt8PtrTy(), B.getInt8PtrTy(), DL.getIntPtrType(Context)); - inferLibFuncAttributes(M, MemCmpName, *TLI); + inferLibFuncAttributes(M, CmpFnName, *TLI); CallInst *CI = B.CreateCall( - MemCmp, {castToCStr(Ptr1, B), castToCStr(Ptr2, B), Len}, MemCmpName); + CmpFn, {castToCStr(Ptr1, B), castToCStr(Ptr2, B), Len}, CmpFnName); if (const Function *F = - dyn_cast(MemCmp.getCallee()->stripPointerCasts())) + dyn_cast(CmpFn.getCallee()->stripPointerCasts())) CI->setCallingConv(F->getCallingConv()); return CI; } +Value *llvm::emitMemCmp(Value *Ptr1, Value *Ptr2, Value *Len, IRBuilder<> &B, + const DataLayout &DL, const TargetLibraryInfo *TLI) { + return emitMemCmpOrBcmp(LibFunc_memcmp, Ptr1, Ptr2, Len, B, DL, TLI); +} + +Value *llvm::emitBCmp(Value *Ptr1, Value *Ptr2, Value *Len, IRBuilder<> &B, + const DataLayout &DL, const TargetLibraryInfo *TLI) { + return emitMemCmpOrBcmp(LibFunc_bcmp, Ptr1, Ptr2, Len, B, DL, TLI); +} + /// Append a suffix to the function name according to the type of 'Op'. static void appendTypeSuffix(Value *Op, StringRef &Name, SmallString<20> &NameBuffer) { diff --git a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp index da368b2..86df933 100644 --- a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp +++ b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp @@ -831,18 +831,9 @@ Value *LibCallSimplifier::optimizeMemChr(CallInst *CI, IRBuilder<> &B) { return B.CreateGEP(B.getInt8Ty(), SrcStr, B.getInt64(I), "memchr"); } -Value *LibCallSimplifier::optimizeMemCmp(CallInst *CI, IRBuilder<> &B) { - Value *LHS = CI->getArgOperand(0), *RHS = CI->getArgOperand(1); - - if (LHS == RHS) // memcmp(s,s,x) -> 0 - return Constant::getNullValue(CI->getType()); - - // Make sure we have a constant length. - ConstantInt *LenC = dyn_cast(CI->getArgOperand(2)); - if (!LenC) - return nullptr; - - uint64_t Len = LenC->getZExtValue(); +static Value *optimizeMemCmpConstantSize(CallInst *CI, Value *LHS, Value *RHS, + uint64_t Len, IRBuilder<> &B, + const DataLayout &DL) { if (Len == 0) // memcmp(s1,s2,0) -> 0 return Constant::getNullValue(CI->getType()); @@ -912,6 +903,28 @@ Value *LibCallSimplifier::optimizeMemCmp(CallInst *CI, IRBuilder<> &B) { Ret = 1; return ConstantInt::get(CI->getType(), Ret); } + return nullptr; +} + +Value *LibCallSimplifier::optimizeMemCmp(CallInst *CI, IRBuilder<> &B) { + Value *LHS = CI->getArgOperand(0), *RHS = CI->getArgOperand(1); + Value *Size = CI->getArgOperand(2); + + if (LHS == RHS) // memcmp(s,s,x) -> 0 + return Constant::getNullValue(CI->getType()); + + // Handle constant lengths. + if (ConstantInt *LenC = dyn_cast(Size)) + if (Value *Res = optimizeMemCmpConstantSize(CI, LHS, RHS, + LenC->getZExtValue(), B, DL)) + return Res; + + // memcmp(x, y, Len) == 0 -> bcmp(x, y, Len) == 0 + // `bcmp` can be more efficient than memcmp because it only has to know that + // there is a difference, not where is is. + if (isOnlyUsedInZeroEqualityComparison(CI) && TLI->has(LibFunc_bcmp)) { + return emitBCmp(LHS, RHS, Size, B, DL, TLI); + } return nullptr; } @@ -1137,10 +1150,10 @@ static Value *optimizeTrigReflections(CallInst *Call, LibFunc Func, IRBuilder<> &B) { if (!isa(Call)) return nullptr; - + IRBuilder<>::FastMathFlagGuard Guard(B); B.setFastMathFlags(Call->getFastMathFlags()); - + // TODO: Can this be shared to also handle LLVM intrinsics? Value *X; switch (Func) { diff --git a/llvm/test/CodeGen/X86/memcmp.ll b/llvm/test/CodeGen/X86/memcmp.ll index 83210b4..06e1cda 100644 --- a/llvm/test/CodeGen/X86/memcmp.ll +++ b/llvm/test/CodeGen/X86/memcmp.ll @@ -1340,3 +1340,70 @@ define i32 @huge_length(i8* %X, i8* %Y) nounwind { %m = tail call i32 @memcmp(i8* %X, i8* %Y, i64 9223372036854775807) nounwind ret i32 %m } + +define i1 @huge_length_eq(i8* %X, i8* %Y) nounwind { +; X86-LABEL: huge_length_eq: +; X86: # %bb.0: +; X86-NEXT: pushl $2147483647 # imm = 0x7FFFFFFF +; X86-NEXT: pushl $-1 +; X86-NEXT: pushl {{[0-9]+}}(%esp) +; X86-NEXT: pushl {{[0-9]+}}(%esp) +; X86-NEXT: calll memcmp +; X86-NEXT: addl $16, %esp +; X86-NEXT: testl %eax, %eax +; X86-NEXT: sete %al +; X86-NEXT: retl +; +; X64-LABEL: huge_length_eq: +; X64: # %bb.0: +; X64-NEXT: pushq %rax +; X64-NEXT: movabsq $9223372036854775807, %rdx # imm = 0x7FFFFFFFFFFFFFFF +; X64-NEXT: callq memcmp +; X64-NEXT: testl %eax, %eax +; X64-NEXT: sete %al +; X64-NEXT: popq %rcx +; X64-NEXT: retq + + %m = tail call i32 @memcmp(i8* %X, i8* %Y, i64 9223372036854775807) nounwind + %c = icmp eq i32 %m, 0 + ret i1 %c +} + +; This checks non-constant sizes. +define i32 @nonconst_length(i8* %X, i8* %Y, i64 %size) nounwind { +; X86-LABEL: nonconst_length: +; X86: # %bb.0: +; X86-NEXT: jmp memcmp # TAILCALL +; +; X64-LABEL: nonconst_length: +; X64: # %bb.0: +; X64-NEXT: jmp memcmp # TAILCALL + %m = tail call i32 @memcmp(i8* %X, i8* %Y, i64 %size) nounwind + ret i32 %m +} + +define i1 @nonconst_length_eq(i8* %X, i8* %Y, i64 %size) nounwind { +; X86-LABEL: nonconst_length_eq: +; X86: # %bb.0: +; X86-NEXT: pushl {{[0-9]+}}(%esp) +; X86-NEXT: pushl {{[0-9]+}}(%esp) +; X86-NEXT: pushl {{[0-9]+}}(%esp) +; X86-NEXT: pushl {{[0-9]+}}(%esp) +; X86-NEXT: calll memcmp +; X86-NEXT: addl $16, %esp +; X86-NEXT: testl %eax, %eax +; X86-NEXT: sete %al +; X86-NEXT: retl +; +; X64-LABEL: nonconst_length_eq: +; X64: # %bb.0: +; X64-NEXT: pushq %rax +; X64-NEXT: callq memcmp +; X64-NEXT: testl %eax, %eax +; X64-NEXT: sete %al +; X64-NEXT: popq %rcx +; X64-NEXT: retq + %m = tail call i32 @memcmp(i8* %X, i8* %Y, i64 %size) nounwind + %c = icmp eq i32 %m, 0 + ret i1 %c +} diff --git a/llvm/test/Transforms/InferFunctionAttrs/annotate.ll b/llvm/test/Transforms/InferFunctionAttrs/annotate.ll index 161873b..02278161 100644 --- a/llvm/test/Transforms/InferFunctionAttrs/annotate.ll +++ b/llvm/test/Transforms/InferFunctionAttrs/annotate.ll @@ -1,5 +1,5 @@ -; RUN: opt < %s -mtriple=x86_64-- -inferattrs -S | FileCheck %s -; RUN: opt < %s -mtriple=x86_64-- -passes=inferattrs -S | FileCheck %s +; RUN: opt < %s -mtriple=x86_64-- -inferattrs -S | FileCheck -check-prefix=CHECK-UNKNOWN %s +; RUN: opt < %s -mtriple=x86_64-- -passes=inferattrs -S | FileCheck -check-prefix=CHECK-UNKNOWN %s ; RUN: opt < %s -mtriple=x86_64-apple-macosx10.8.0 -inferattrs -S | FileCheck -check-prefix=CHECK -check-prefix=CHECK-DARWIN %s ; RUN: opt < %s -mtriple=x86_64-unknown-linux-gnu -inferattrs -S | FileCheck -check-prefix=CHECK -check-prefix=CHECK-LINUX %s ; RUN: opt < %s -mtriple=nvptx -inferattrs -S | FileCheck -check-prefix=CHECK-NVPTX %s @@ -241,7 +241,10 @@ declare i64 @atol(i8*) ; CHECK: declare i64 @atoll(i8* nocapture) [[G1]] declare i64 @atoll(i8*) -; CHECK: declare i32 @bcmp(i8* nocapture, i8* nocapture, i64) [[G1]] +; CHECK-DARWIN: declare i32 @bcmp(i8* nocapture, i8* nocapture, i64) [[G1]] +; CHECK-LINUX: declare i32 @bcmp(i8* nocapture, i8* nocapture, i64) [[G1]] +; CHECK-UNKNOWN-NOT: declare i32 @bcmp(i8* nocapture, i8* nocapture, i64) [[G1]] +; CHECK-NVPTX-NOT: declare i32 @bcmp(i8* nocapture, i8* nocapture, i64) [[G1]] declare i32 @bcmp(i8*, i8*, i64) ; CHECK: declare void @bcopy(i8* nocapture readonly, i8* nocapture, i64) [[G0]] diff --git a/llvm/test/Transforms/InstCombine/memcmp-1.ll b/llvm/test/Transforms/InstCombine/memcmp-1.ll index 96516f4..a82f861 100644 --- a/llvm/test/Transforms/InstCombine/memcmp-1.ll +++ b/llvm/test/Transforms/InstCombine/memcmp-1.ll @@ -1,6 +1,7 @@ ; Test that the memcmp library call simplifier works correctly. ; -; RUN: opt < %s -instcombine -S | FileCheck %s +; RUN: opt < %s -instcombine -S | FileCheck --check-prefix=CHECK --check-prefix=NOBCMP %s +; RUN: opt < %s -instcombine -mtriple=x86_64-unknown-linux-gnu -S | FileCheck --check-prefix=CHECK --check-prefix=BCMP %s target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128-n8:16:32:64" @@ -130,3 +131,21 @@ define i1 @test_simplify9(i16 %x, i16 %y) { %cmp = icmp eq i32 %call, 0 ret i1 %cmp } + +; Check memcmp(mem1, mem2, size)==0 -> bcmp(mem1, mem2, size)==0 + +define i1 @test_simplify10(i8* %mem1, i8* %mem2, i32 %size) { +; NOBCMP-LABEL: @test_simplify10( +; NOBCMP-NEXT: [[CALL:%.*]] = call i32 @memcmp(i8* %mem1, i8* %mem2, i32 %size) +; NOBCMP-NEXT: [[CMP:%.*]] = icmp eq i32 [[CALL]], 0 +; NOBCMP-NEXT: ret i1 [[CMP]] +; +; BCMP-LABEL: @test_simplify10( +; BCMP-NEXT: [[CALL:%.*]] = call i32 @bcmp(i8* %mem1, i8* %mem2, i32 %size) +; BCMP-NEXT: [[CMP:%.*]] = icmp eq i32 [[CALL]], 0 +; BCMP-NEXT: ret i1 [[CMP]] +; + %call = call i32 @memcmp(i8* %mem1, i8* %mem2, i32 %size) + %cmp = icmp eq i32 %call, 0 + ret i1 %cmp +} diff --git a/llvm/test/Transforms/InstCombine/strcmp-1.ll b/llvm/test/Transforms/InstCombine/strcmp-1.ll index 9bc1fc6..4dfda04 100644 --- a/llvm/test/Transforms/InstCombine/strcmp-1.ll +++ b/llvm/test/Transforms/InstCombine/strcmp-1.ll @@ -1,5 +1,6 @@ ; Test that the strcmp library call simplifier works correctly. -; RUN: opt < %s -instcombine -S | FileCheck %s +; RUN: opt < %s -instcombine -S | FileCheck %s --check-prefix=NOBCMP +; RUN: opt < %s -instcombine -mtriple=unknown-unknown-linux-gnu -S | FileCheck %s --check-prefix=BCMP target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128" @@ -80,3 +81,24 @@ define i32 @test6(i8* %str) { %temp1 = call i32 @strcmp(i8* %str, i8* %str) ret i32 %temp1 } + +; strcmp(x, y) == 0 -> bcmp(x, y, ) +define i1 @test7(i1 %b) { +; BCMP-LABEL: @test7( +; BCMP: %bcmp = call i32 @bcmp(i8* getelementptr inbounds ([6 x i8], [6 x i8]* @hello, i32 0, i32 0), i8* %str2, i32 5) +; BCMP: %res = icmp eq i32 %bcmp, 0 +; BCMP: ret i1 %res + +; NOBCMP-LABEL: @test7( +; NOBCMP: %memcmp = call i32 @memcmp(i8* getelementptr inbounds ([6 x i8], [6 x i8]* @hello, i32 0, i32 0), i8* %str2, i32 5) +; NOBCMP: %res = icmp eq i32 %memcmp, 0 +; NOBCMP: ret i1 %res + + %str1 = getelementptr inbounds [6 x i8], [6 x i8]* @hello, i32 0, i32 0 + %temp1 = getelementptr inbounds [5 x i8], [5 x i8]* @hell, i32 0, i32 0 + %temp2 = getelementptr inbounds [5 x i8], [5 x i8]* @bell, i32 0, i32 0 + %str2 = select i1 %b, i8* %temp1, i8* %temp2 + %temp3 = call i32 @strcmp(i8* %str1, i8* %str2) + %res = icmp eq i32 %temp3, 0 + ret i1 %res +} -- 2.7.4