diff options
Diffstat (limited to 'llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp')
| -rw-r--r-- | llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp | 28 |
1 files changed, 23 insertions, 5 deletions
diff --git a/llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp b/llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp index c4b43e1b5126..4bd650b37792 100644 --- a/llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp +++ b/llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp @@ -2195,13 +2195,24 @@ void AArch64AsmPrinter::emitPtrauthBranch(const MachineInstr *MI) { if (BrTarget == AddrDisc) report_fatal_error("Branch target is signed with its own value"); - // If we are printing BLRA pseudo instruction, then x16 and x17 are - // implicit-def'ed by the MI and AddrDisc is not used as any other input, so - // try to save one MOV by setting MayUseAddrAsScratch. + // If we are printing BLRA pseudo, try to save one MOV by making use of the + // fact that x16 and x17 are described as clobbered by the MI instruction and + // AddrDisc is not used as any other input. + // + // Back in the day, emitPtrauthDiscriminator was restricted to only returning + // either x16 or x17, meaning the returned register is always among the + // implicit-def'ed registers of BLRA pseudo. Now this property can be violated + // if isX16X17Safer predicate is false, thus manually check if AddrDisc is + // among x16 and x17 to prevent clobbering unexpected registers. + // // Unlike BLRA, BRA pseudo is used to perform computed goto, and thus not // declared as clobbering x16/x17. + // + // FIXME: Make use of `killed` flags and register masks instead. + bool AddrDiscIsImplicitDef = + IsCall && (AddrDisc == AArch64::X16 || AddrDisc == AArch64::X17); Register DiscReg = emitPtrauthDiscriminator(Disc, AddrDisc, AArch64::X17, - /*MayUseAddrAsScratch=*/IsCall); + AddrDiscIsImplicitDef); bool IsZeroDisc = DiscReg == AArch64::XZR; unsigned Opc; @@ -2930,8 +2941,15 @@ void AArch64AsmPrinter::emitInstruction(const MachineInstr *MI) { // See the comments in emitPtrauthBranch. if (Callee == AddrDisc) report_fatal_error("Call target is signed with its own value"); + + // After isX16X17Safer predicate was introduced, emitPtrauthDiscriminator is + // no longer restricted to only reusing AddrDisc when it is X16 or X17 + // (which are implicit-def'ed by AUTH_TCRETURN pseudos), thus impose this + // restriction manually not to clobber an unexpected register. + bool AddrDiscIsImplicitDef = + AddrDisc == AArch64::X16 || AddrDisc == AArch64::X17; Register DiscReg = emitPtrauthDiscriminator(Disc, AddrDisc, ScratchReg, - /*MayUseAddrAsScratch=*/true); + AddrDiscIsImplicitDef); const bool IsZero = DiscReg == AArch64::XZR; const unsigned Opcodes[2][2] = {{AArch64::BRAA, AArch64::BRAAZ}, |