From 14c1e987546ef161769aa619bb9de21c943721ec Mon Sep 17 00:00:00 2001 From: Peter Smith Date: Wed, 1 Apr 2020 08:43:07 +0100 Subject: [ARM] Remove condition that could never be true From Arm v8 Architecture Reference Manual F5.1.84 LDREXD The ldrexd instruction in Arm state has the following conditions: t = UInt(Rt); t2 = t + 1; n = UInt(Rn); if Rt<0> == '1' || t2 == 15 || n == 15 then UNPREDICTABLE; In when Rt is odd or if Rt is 14 (making t2 15). In the implementation when the pair is the UNPREDICTABLE R14_R15 we would ideally return SOFT_FAIL. We can't because there is no R14_R15 value for us to return so we fail early returning FAIL. The early return for registers outside the bounds of the table means the check for Rt == 14 (0xE) redundant which causes a static analyzer to flag the condition as never being true. To fix the warning I've removed the check and replaced with a comment explaining the difference with the specification. Fixes pr41660 Differential Revision: https://reviews.llvm.org/D77463 --- llvm/lib/Target/ARM/Disassembler/ARMDisassembler.cpp | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) (limited to 'llvm/lib/Target/ARM/Disassembler/ARMDisassembler.cpp') diff --git a/llvm/lib/Target/ARM/Disassembler/ARMDisassembler.cpp b/llvm/lib/Target/ARM/Disassembler/ARMDisassembler.cpp index 6938814..54ff0d9 100644 --- a/llvm/lib/Target/ARM/Disassembler/ARMDisassembler.cpp +++ b/llvm/lib/Target/ARM/Disassembler/ARMDisassembler.cpp @@ -1225,10 +1225,12 @@ static DecodeStatus DecodeGPRPairRegisterClass(MCInst &Inst, unsigned RegNo, uint64_t Address, const void *Decoder) { DecodeStatus S = MCDisassembler::Success; + // According to the Arm ARM RegNo = 14 is undefined, but we return fail + // rather than SoftFail as there is no GPRPair table entry for index 7. if (RegNo > 13) return MCDisassembler::Fail; - if ((RegNo & 1) || RegNo == 0xe) + if (RegNo & 1) S = MCDisassembler::SoftFail; unsigned RegisterPair = GPRPairDecoderTable[RegNo/2]; -- cgit v1.1