https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65773
Bug ID: 65773 Summary: [5.1 regression] GCC 5.1 miscompiles LLVM function AArch64InstrInfo::loadRegFromStackSlot() Product: gcc Version: 5.1.0 Status: UNCONFIRMED Keywords: wrong-code Severity: normal Priority: P3 Component: target Assignee: unassigned at gcc dot gnu.org Reporter: wschmidt at gcc dot gnu.org CC: bergner at gcc dot gnu.org, jakub at gcc dot gnu.org, rguenth at gcc dot gnu.org Host: powerpc64*-linux-gnu Target: powerpc64*-linux-gnu Build: powerpc64*-linux-gnu I built gcc from branches/gcc-5-branch yesterday and used it to build Clang/LLVM as an acid test. Unfortunately the test suite shows a number of failures. I've traced these down to a miscompile of AArch64InstrInfo::loadRegFromStackSlot( <long argument list omitted> ). The bad code can be seen here: 105eb74c: 00 00 60 38 li r3,0 105eb750: 28 00 41 f9 std r10,40(r1) 105eb754: e4 06 29 79 rldicr r9,r9,0,59 105eb758: 30 00 41 f9 std r10,48(r1) 105eb75c: 21 00 01 99 stb r8,33(r1) 105eb760: 22 00 21 99 stb r9,34(r1) 105eb764: a5 ec 79 48 bl 10d8a408 <_ZN4llvm12MachineInstr10addOp\ erandERNS_15MachineFunctionERKNS_14MachineOperandE+0x8> This calls MachineInstr::addOperand(MachineFunction&, MachineOperand const&) with r3 as the this pointer. Loading zero into the this pointer ahead of the call seems somewhat unhelpful. The same code compiled with the 4.8 gcc I usually use shows: 106a8fa0: 78 cb 25 7f mr r5,r25 106a8fa4: 78 f3 c3 7f mr r3,r30 106a8fa8: 20 00 9e eb ld r28,32(r30) 106a8fac: 78 eb a4 7f mr r4,r29 106a8fb0: 78 d3 46 7f mr r6,r26 106a8fb4: 65 d4 7c 48 bl 10e76418 <_ZNK4llvm12MachineInstr21getR\ egClassConstraintEjPKNS_15TargetInstrInfoEPKNS_18TargetRegisterInfoE+0x8> which is clearly much more reasonable. I'll gather reproduction materials, but wanted to get the bug filed quickly for awareness.