From d32beab637bf1f6ebddeffe147b064f05595ba04 Mon Sep 17 00:00:00 2001 From: Matthias Braun Date: Fri, 24 Apr 2015 01:15:27 +0000 Subject: [PATCH] Improve isTriviallyReMaterializable() documentation. This should make it clear under which narrow circumstances implicit physreg uses are okay when rematerializing and prevent people from accidentally allowing too much when overriding isReallyTriviallyReMaterializable() even with the weaker assert in the RegisterCoalescer. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@235679 91177308-0d34-0410-b5e6-96231b3b80d8 --- include/llvm/Target/TargetInstrInfo.h | 21 ++++++++++++--------- 1 file changed, 12 insertions(+), 9 deletions(-) diff --git a/include/llvm/Target/TargetInstrInfo.h b/include/llvm/Target/TargetInstrInfo.h index 110976a0a82..f9c1e523e5a 100644 --- a/include/llvm/Target/TargetInstrInfo.h +++ b/include/llvm/Target/TargetInstrInfo.h @@ -67,9 +67,11 @@ public: const TargetRegisterInfo *TRI, const MachineFunction &MF) const; - /// isTriviallyReMaterializable - Return true if the instruction is trivially - /// rematerializable, meaning it has no side effects and requires no operands - /// that aren't always available. + /// Return true if the instruction is trivially rematerializable, meaning it + /// has no side effects and requires no operands that aren't always available. + /// This means the only allowed uses are constants and unallocatable physical + /// registers so that the instructions result is independent of the place + /// in the function. bool isTriviallyReMaterializable(const MachineInstr *MI, AliasAnalysis *AA = nullptr) const { return MI->getOpcode() == TargetOpcode::IMPLICIT_DEF || @@ -79,12 +81,13 @@ public: } protected: - /// isReallyTriviallyReMaterializable - For instructions with opcodes for - /// which the M_REMATERIALIZABLE flag is set, this hook lets the target - /// specify whether the instruction is actually trivially rematerializable, - /// taking into consideration its operands. This predicate must return false - /// if the instruction has any side effects other than producing a value, or - /// if it requres any address registers that are not always available. + /// For instructions with opcodes for which the M_REMATERIALIZABLE flag is + /// set, this hook lets the target specify whether the instruction is actually + /// trivially rematerializable, taking into consideration its operands. This + /// predicate must return false if the instruction has any side effects other + /// than producing a value, or if it requres any address registers that are + /// not always available. + /// Requirements must be check as stated in isTriviallyReMaterializable() . virtual bool isReallyTriviallyReMaterializable(const MachineInstr *MI, AliasAnalysis *AA) const { return false; -- 2.34.1