[llvm] r256730 - [X86] Make hasFP constant time
David Majnemer via llvm-commits
llvm-commits at lists.llvm.org
Sun Jan 3 20:49:42 PST 2016
Author: majnemer
Date: Sun Jan 3 22:49:41 2016
New Revision: 256730
URL: http://llvm.org/viewvc/llvm-project?rev=256730&view=rev
Log:
[X86] Make hasFP constant time
We need a frame pointer if there is a push/pop sequence after the
prologue in order to unwind the stack. Scanning the instructions to
figure out if this happened made hasFP not constant-time which is a
violation of expectations. Let's compute this up-front and reuse that
computation when we need it.
Modified:
llvm/trunk/include/llvm/Target/TargetLowering.h
llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
llvm/trunk/lib/Target/X86/X86FrameLowering.cpp
llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
llvm/trunk/lib/Target/X86/X86ISelLowering.h
llvm/trunk/lib/Target/X86/X86InstrInfo.cpp
Modified: llvm/trunk/include/llvm/Target/TargetLowering.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Target/TargetLowering.h?rev=256730&r1=256729&r2=256730&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Target/TargetLowering.h (original)
+++ llvm/trunk/include/llvm/Target/TargetLowering.h Sun Jan 3 22:49:41 2016
@@ -2269,6 +2269,12 @@ public:
return false;
}
+ /// Return true if the MachineFunction contains a COPY which would imply
+ /// HasOpaqueSPAdjustment.
+ virtual bool hasCopyImplyingStackAdjustment(MachineFunction *MF) const {
+ return false;
+ }
+
/// Perform necessary initialization to handle a subset of CSRs explicitly
/// via copies. This function is called at the beginning of instruction
/// selection.
Modified: llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp?rev=256730&r1=256729&r2=256730&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp Sun Jan 3 22:49:41 2016
@@ -633,6 +633,9 @@ bool SelectionDAGISel::runOnMachineFunct
MRI.replaceRegWith(From, To);
}
+ if (TLI->hasCopyImplyingStackAdjustment(MF))
+ MFI->setHasOpaqueSPAdjustment(true);
+
// Freeze the set of reserved registers now that MachineFrameInfo has been
// set up. All the information required by getReservedRegs() should be
// available now.
Modified: llvm/trunk/lib/Target/X86/X86FrameLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86FrameLowering.cpp?rev=256730&r1=256729&r2=256730&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86FrameLowering.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86FrameLowering.cpp Sun Jan 3 22:49:41 2016
@@ -78,23 +78,6 @@ X86FrameLowering::needsFrameIndexResolut
MF.getInfo<X86MachineFunctionInfo>()->getHasPushSequences();
}
-/// usesTheStack - This function checks if any of the users of EFLAGS
-/// copies the EFLAGS. We know that the code that lowers COPY of EFLAGS has
-/// to use the stack, and if we don't adjust the stack we clobber the first
-/// frame index.
-/// See X86InstrInfo::copyPhysReg.
-static bool usesTheStack(const MachineFunction &MF) {
- const MachineRegisterInfo &MRI = MF.getRegInfo();
-
- return any_of(MRI.reg_instructions(X86::EFLAGS),
- [](const MachineInstr &RI) { return RI.isCopy(); });
-}
-
-static bool doesStackUseImplyFP(const MachineFunction &MF) {
- bool IsWin64Prologue = MF.getTarget().getMCAsmInfo()->usesWindowsCFI();
- return IsWin64Prologue && usesTheStack(MF);
-}
-
/// hasFP - Return true if the specified function should have a dedicated frame
/// pointer register. This is true if the function has variable sized allocas
/// or if frame pointer elimination is disabled.
@@ -108,8 +91,7 @@ bool X86FrameLowering::hasFP(const Machi
MFI->isFrameAddressTaken() || MFI->hasOpaqueSPAdjustment() ||
MF.getInfo<X86MachineFunctionInfo>()->getForceFramePointer() ||
MMI.callsUnwindInit() || MMI.hasEHFunclets() || MMI.callsEHReturn() ||
- MFI->hasStackMap() || MFI->hasPatchPoint() ||
- doesStackUseImplyFP(MF));
+ MFI->hasStackMap() || MFI->hasPatchPoint());
}
static unsigned getSUBriOpcode(unsigned IsLP64, int64_t Imm) {
@@ -961,11 +943,11 @@ void X86FrameLowering::emitPrologue(Mach
// push and pop from the stack.
if (Is64Bit && !Fn->hasFnAttribute(Attribute::NoRedZone) &&
!TRI->needsStackRealignment(MF) &&
- !MFI->hasVarSizedObjects() && // No dynamic alloca.
- !MFI->adjustsStack() && // No calls.
- !IsWin64CC && // Win64 has no Red Zone
- !usesTheStack(MF) && // Don't push and pop.
- !MF.shouldSplitStack()) { // Regular stack
+ !MFI->hasVarSizedObjects() && // No dynamic alloca.
+ !MFI->adjustsStack() && // No calls.
+ !IsWin64CC && // Win64 has no Red Zone
+ !MFI->hasOpaqueSPAdjustment() && // Don't push and pop.
+ !MF.shouldSplitStack()) { // Regular stack
uint64_t MinSize = X86FI->getCalleeSavedFrameSize();
if (HasFP) MinSize += SlotSize;
StackSize = std::max(MinSize, StackSize > 128 ? StackSize - 128 : 0);
Modified: llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86ISelLowering.cpp?rev=256730&r1=256729&r2=256730&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86ISelLowering.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86ISelLowering.cpp Sun Jan 3 22:49:41 2016
@@ -27982,6 +27982,18 @@ bool X86TargetLowering::isTypeDesirableF
}
}
+/// This function checks if any of the users of EFLAGS copies the EFLAGS. We
+/// know that the code that lowers COPY of EFLAGS has to use the stack, and if
+/// we don't adjust the stack we clobber the first frame index.
+/// See X86InstrInfo::copyPhysReg.
+bool X86TargetLowering::hasCopyImplyingStackAdjustment(
+ MachineFunction *MF) const {
+ const MachineRegisterInfo &MRI = MF->getRegInfo();
+
+ return any_of(MRI.reg_instructions(X86::EFLAGS),
+ [](const MachineInstr &RI) { return RI.isCopy(); });
+}
+
/// IsDesirableToPromoteOp - This method query the target whether it is
/// beneficial for dag combiner to promote the specified node. If true, it
/// should return the desired promotion type by reference.
Modified: llvm/trunk/lib/Target/X86/X86ISelLowering.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86ISelLowering.h?rev=256730&r1=256729&r2=256730&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86ISelLowering.h (original)
+++ llvm/trunk/lib/Target/X86/X86ISelLowering.h Sun Jan 3 22:49:41 2016
@@ -697,6 +697,10 @@ namespace llvm {
/// and some i16 instructions are slow.
bool IsDesirableToPromoteOp(SDValue Op, EVT &PVT) const override;
+ /// Return true if the MachineFunction contains a COPY which would imply
+ /// HasOpaqueSPAdjustment.
+ bool hasCopyImplyingStackAdjustment(MachineFunction *MF) const override;
+
MachineBasicBlock *
EmitInstrWithCustomInserter(MachineInstr *MI,
MachineBasicBlock *MBB) const override;
Modified: llvm/trunk/lib/Target/X86/X86InstrInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86InstrInfo.cpp?rev=256730&r1=256729&r2=256730&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86InstrInfo.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86InstrInfo.cpp Sun Jan 3 22:49:41 2016
@@ -4453,7 +4453,8 @@ void X86InstrInfo::copyPhysReg(MachineBa
// such as TF/IF/DF, which LLVM doesn't model.
//
// Notice that we have to adjust the stack if we don't want to clobber the
- // first frame index. See X86FrameLowering.cpp - usesTheStack.
+ // first frame index.
+ // See X86ISelLowering.cpp - X86::hasCopyImplyingStackAdjustment.
bool AXDead = (Reg == AX) ||
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