diff options
Diffstat (limited to 'llvm/lib')
| -rw-r--r-- | llvm/lib/Target/README.txt | 3 | ||||
| -rw-r--r-- | llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp | 54 |
2 files changed, 52 insertions, 5 deletions
diff --git a/llvm/lib/Target/README.txt b/llvm/lib/Target/README.txt index 0fa56e66747..52a334a6174 100644 --- a/llvm/lib/Target/README.txt +++ b/llvm/lib/Target/README.txt @@ -1268,7 +1268,8 @@ int foo (void) { .. else if (strchr ("<>", *intel_parser.op_string) -Those should be turned into a switch. +Those should be turned into a switch. SimplifyLibCalls only gets the second +case. //===---------------------------------------------------------------------===// diff --git a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp index 0d0b77a6a3e..f6cc431656b 100644 --- a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp +++ b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp @@ -762,11 +762,9 @@ Value *LibCallSimplifier::optimizeMemChr(CallInst *CI, IRBuilder<> &B) { if (LenC && LenC->isNullValue()) return Constant::getNullValue(CI->getType()); - // Check if all arguments are constants. If so, we can constant fold. + // From now on we need at least constant length and string. StringRef Str; - if (!CharC || !LenC || - !getConstantStringInfo(SrcStr, Str, /*Offset=*/0, - /*TrimAtNul=*/false)) + if (!LenC || !getConstantStringInfo(SrcStr, Str, 0, /*TrimAtNul=*/false)) return nullptr; // Truncate the string to LenC. If Str is smaller than LenC we will still only @@ -774,6 +772,54 @@ Value *LibCallSimplifier::optimizeMemChr(CallInst *CI, IRBuilder<> &B) { // return null if we don't find the char. Str = Str.substr(0, LenC->getZExtValue()); + // If the char is variable but the input str and length are not we can turn + // this memchr call into a simple bit field test. Of course this only works + // when the return value is only checked against null. + // + // It would be really nice to reuse switch lowering here but we can't change + // the CFG at this point. + // + // memchr("\r\n", C, 2) != nullptr -> (C & ((1 << '\r') | (1 << '\n'))) != 0 + // after bounds check. + if (!CharC && !Str.empty() && isOnlyUsedInZeroEqualityComparison(CI)) { + unsigned char Max = *std::max_element(Str.begin(), Str.end()); + + // Make sure the bit field we're about to create fits in a register on the + // target. + // FIXME: On a 64 bit architecture this prevents us from using the + // interesting range of alpha ascii chars. We could do better by emitting + // two bitfields or shifting the range by 64 if no lower chars are used. + if (!DL.fitsInLegalInteger(Max + 1)) + return nullptr; + + // For the bit field use a power-of-2 type with at least 8 bits to avoid + // creating unnecessary illegal types. + unsigned char Width = NextPowerOf2(std::max((unsigned char)7, Max)); + + // Now build the bit field. + APInt Bitfield(Width, 0); + for (char C : Str) + Bitfield.setBit((unsigned char)C); + Value *BitfieldC = B.getInt(Bitfield); + + // First check that the bit field access is within bounds. + Value *C = B.CreateZExtOrTrunc(CI->getArgOperand(1), BitfieldC->getType()); + Value *Bounds = B.CreateICmp(ICmpInst::ICMP_ULT, C, B.getIntN(Width, Width), + "memchr.bounds"); + + // Create code that checks if the given bit is set in the field. + Value *Shl = B.CreateShl(B.getIntN(Width, 1ULL), C); + Value *Bits = B.CreateIsNotNull(B.CreateAnd(Shl, BitfieldC), "memchr.bits"); + + // Finally merge both checks and cast to pointer type. The inttoptr + // implicitly zexts the i1 to intptr type. + return B.CreateIntToPtr(B.CreateAnd(Bounds, Bits, "memchr"), CI->getType()); + } + + // Check if all arguments are constants. If so, we can constant fold. + if (!CharC) + return nullptr; + // Compute the offset. size_t I = Str.find(CharC->getSExtValue() & 0xFF); if (I == StringRef::npos) // Didn't find the char. memchr returns null. |
