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[MachineLICM] Hoist TOC-based address instructions

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Add condition for MachineLICM to safely hoist instructions that utilize
non constant registers that are reserved.

On PPC, global variable access is done through the table of contents (TOC)
which is always in register X2.  The ABI reserves this register in any
functions that have calls or access global variables.

A call through a function pointer involves saving, changing and restoring
this register around the call and thus MachineLICM does not consider it to
be invariant. We can however guarantee the register is preserved across the
call and thus is invariant.

Differential Revision: https://reviews.llvm.org/D33562

llvm-svn: 305490
This commit is contained in:
Lei Huang 2017-06-15 18:29:59 +00:00
parent be435df139
commit cdf47c5983
5 changed files with 140 additions and 2 deletions
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10
include/llvm/Target/TargetRegisterInfo.h
View File

@ -497,6 +497,16 @@ public:
/// function. Used by MachineRegisterInfo::isConstantPhysReg().
virtual bool isConstantPhysReg(unsigned PhysReg) const { return false; }
/// Physical registers that may be modified within a function but are
/// guaranteed to be restored before any uses. This is useful for targets that
/// have call sequences where a GOT register may be updated by the caller
/// prior to a call and is guaranteed to be restored (also by the caller)
/// after the call.
virtual bool isCallerPreservedPhysReg(unsigned PhysReg,
const MachineFunction &MF) const {
return false;
}
/// Prior to adding the live-out mask to a stackmap or patchpoint
/// instruction, provide the target the opportunity to adjust it (mainly to
/// remove pseudo-registers that should be ignored).

7
lib/CodeGen/MachineLICM.cpp
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@ -895,8 +895,11 @@ bool MachineLICM::IsLoopInvariantInst(MachineInstr &I) {
// If the physreg has no defs anywhere, it's just an ambient register
// and we can freely move its uses. Alternatively, if it's allocatable,
// it could get allocated to something with a def during allocation.
if (!MRI->isConstantPhysReg(Reg))
return false;
// However, if the physreg is known to always be caller saved/restored
// then this use is safe to hoist.
if (!MRI->isConstantPhysReg(Reg) &&
!(TRI->isCallerPreservedPhysReg(Reg, *I.getParent()->getParent())))
return false;
// Otherwise it's safe to move.
continue;
} else if (!MO.isDead()) {

14
lib/Target/PowerPC/PPCRegisterInfo.cpp
View File

@ -273,6 +273,20 @@ BitVector PPCRegisterInfo::getReservedRegs(const MachineFunction &MF) const {
return Reserved;
}
bool PPCRegisterInfo::isCallerPreservedPhysReg(unsigned PhysReg,
const MachineFunction &MF) const {
assert(TargetRegisterInfo::isPhysicalRegister(PhysReg));
if (TM.isELFv2ABI() && PhysReg == PPC::X2) {
// X2 is guaranteed to be preserved within a function if it is reserved.
// The reason it's reserved is that it's the TOC pointer (and the function
// uses the TOC). In functions where it isn't reserved (i.e. leaf functions
// with no TOC access), we can't claim that it is preserved.
return (getReservedRegs(MF).test(PPC::X2));
} else {
return false;
}
}
unsigned PPCRegisterInfo::getRegPressureLimit(const TargetRegisterClass *RC,
MachineFunction &MF) const {
const PPCFrameLowering *TFI = getFrameLowering(MF);

1
lib/Target/PowerPC/PPCRegisterInfo.h
View File

@ -83,6 +83,7 @@ public:
void adjustStackMapLiveOutMask(uint32_t *Mask) const override;
BitVector getReservedRegs(const MachineFunction &MF) const override;
bool isCallerPreservedPhysReg(unsigned PhysReg, const MachineFunction &MF) const override;
/// We require the register scavenger.
bool requiresRegisterScavenging(const MachineFunction &MF) const override {

110
test/CodeGen/PowerPC/licm-tocReg.ll Normal file
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@ -0,0 +1,110 @@
; RUN: llc -verify-machineinstrs -mtriple=powerpc64le-unknown-linux-gnu < %s | FileCheck %s
; The instructions ADDIStocHA/LDtocL are used to calculate the address of
; globals. The ones that are in bb.3.if.end could not be hoisted by Machine
; LICM due to BCTRL_LDinto_toc in bb2.if.then. This call causes the compiler
; to insert a save TOC to stack before the call and load into X2 to restore TOC
; after. By communicating to Machine LICM that X2 is guaranteed to have the
; same value before and after BCTRL_LDinto_toc, these instructions can be
; hoisted out of bb.3.if.end to outside of the loop.
; Pre Machine LICM MIR
;
;body:
; bb.0.entry:
; successors: %bb.2.if.then(0x40000000), %bb.3.if.end(0x40000000)
; liveins: %x3
;
; %4 = COPY %x3
; %5 = ADDIStocHA %x2, @ga
; %6 = LDtocL @ga, killed %5 :: (load 8 from got)
; %7 = LWZ 0, %6 :: (volatile dereferenceable load 4 from @ga)
; %8 = ADDIStocHA %x2, @gb
; %9 = LDtocL @gb, killed %8 :: (load 8 from got)
; %10 = LWZ 0, killed %9 :: (volatile dereferenceable load 4 from @gb)
; %0 = LWZ 0, %6 :: (volatile dereferenceable load 4 from @ga)
; %11 = CMPW killed %7, killed %10
; BCC 44, killed %11, %bb.2.if.then
; B %bb.3.if.end
;
; bb.2.if.then:
; %1 = PHI %0, %bb.0.entry, %3, %bb.3.if.end
; ADJCALLSTACKDOWN 32, 0, implicit-def dead %r1, implicit %r1
; %20 = COPY %x2
; STD %20, 24, %x1 :: (store 8 into stack + 24)
; %21 = EXTSW_32_64 %1
; %x3 = COPY %21
; %x12 = COPY %4
; MTCTR8 %4, implicit-def %ctr8
; BCTRL8_LDinto_toc 24, %x1, csr_svr464_altivec, implicit-def dead %lr8, implicit-def dead %x2, implicit %ctr8, implicit %rm, implicit %x3, implicit %x12, implicit %x2, implicit-def %r1, implicit-def %x3
; ADJCALLSTACKUP 32, 0, implicit-def dead %r1, implicit %r1
; %22 = COPY %x3
; %x3 = COPY %22
; BLR8 implicit %lr8, implicit %rm, implicit %x3
;
; bb.3.if.end:
; successors: %bb.2.if.then(0x04000000), %bb.3.if.end(0x7c000000)
;
; %2 = PHI %0, %bb.0.entry, %3, %bb.3.if.end
; %12 = ADDI %2, 1
; %13 = ADDIStocHA %x2, @ga
; %14 = LDtocL @ga, killed %13 :: (load 8 from got)
; STW killed %12, 0, %14 :: (volatile store 4 into @ga)
; %15 = LWZ 0, %14 :: (volatile dereferenceable load 4 from @ga)
; %16 = ADDIStocHA %x2, @gb
; %17 = LDtocL @gb, killed %16 :: (load 8 from got)
; %18 = LWZ 0, killed %17 :: (volatile dereferenceable load 4 from @gb)
; %3 = LWZ 0, %14 :: (volatile dereferenceable load 4 from @ga)
; %19 = CMPW killed %15, killed %18
; BCC 44, killed %19, %bb.2.if.then
; B %bb.3.if.end
@ga = external global i32, align 4
@gb = external global i32, align 4
; Function Attrs: nounwind
define signext i32 @test(i32 (i32)* nocapture %FP) local_unnamed_addr #0 {
; CHECK-LABEL: test:
; CHECK: # BB#0: # %entry
; CHECK-NEXT: addis 4, 2, .LC0@toc@ha
; CHECK-NEXT: addis 5, 2, .LC1@toc@ha
; CHECK-NEXT: ld 4, .LC0@toc@l(4)
; CHECK-NEXT: ld 5, .LC1@toc@l(5)
; CHECK-NEXT: lwz 6, 0(4)
; CHECK-NEXT: lwz 5, 0(5)
; CHECK-NEXT: cmpw 6, 5
; CHECK-NEXT: lwz 5, 0(4)
; CHECK-NEXT: mr 4, 3
; CHECK-NEXT: bgt 0, .LBB0_3
; CHECK-NEXT: # BB#1:
; CHECK-NEXT: addis 3, 2, .LC0@toc@ha
; CHECK-NEXT: addis 6, 2, .LC1@toc@ha
; CHECK-NEXT: ld 3, .LC0@toc@l(3)
; CHECK-NEXT: ld 6, .LC1@toc@l(6)
; CHECK-NEXT: .p2align 5
; CHECK-NEXT: .LBB0_2: # %if.end
; CHECK-NOT: addis {{[0-9]+}}, 2, .LC0@toc@ha
; CHECK-NOT: addis {{[0-9]+}}, 2, .LC1@toc@ha
; CHECK: blr
entry:
%0 = load volatile i32, i32* @ga, align 4
%1 = load volatile i32, i32* @gb, align 4
%cmp1 = icmp sgt i32 %0, %1
%2 = load volatile i32, i32* @ga, align 4
br i1 %cmp1, label %if.then, label %if.end
if.then: ; preds = %if.end, %entry
%.lcssa = phi i32 [ %2, %entry ], [ %6, %if.end ]
%call = tail call signext i32 %FP(i32 signext %.lcssa) #1
ret i32 %call
if.end: ; preds = %entry, %if.end
%3 = phi i32 [ %6, %if.end ], [ %2, %entry ]
%inc = add nsw i32 %3, 1
store volatile i32 %inc, i32* @ga, align 4
%4 = load volatile i32, i32* @ga, align 4
%5 = load volatile i32, i32* @gb, align 4
%cmp = icmp sgt i32 %4, %5
%6 = load volatile i32, i32* @ga, align 4
br i1 %cmp, label %if.then, label %if.end
}