[llvm] r218789 - ARM: allow copying of CPSR when all else fails.
Tim Northover
tnorthover at apple.com
Wed Oct 1 12:21:04 PDT 2014
Author: tnorthover
Date: Wed Oct 1 14:21:03 2014
New Revision: 218789
URL: http://llvm.org/viewvc/llvm-project?rev=218789&view=rev
Log:
ARM: allow copying of CPSR when all else fails.
As with x86 and AArch64, certain situations can arise where we need to spill
CPSR in the middle of a calculation. These should be avoided where possible
(MRS/MSR is rather expensive), which ARM is actually better at than the other
two since it tries to Glue defs to uses, but as a last ditch effort, copying is
better than crashing.
rdar://problem/18011155
Added:
llvm/trunk/test/CodeGen/ARM/copy-cpsr.ll
Modified:
llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp
llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.h
llvm/trunk/lib/Target/ARM/ARMBaseRegisterInfo.cpp
Modified: llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp?rev=218789&r1=218788&r2=218789&view=diff
==============================================================================
--- llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp (original)
+++ llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.cpp Wed Oct 1 14:21:03 2014
@@ -698,6 +698,49 @@ unsigned ARMBaseInstrInfo::getInstBundle
return Size;
}
+void ARMBaseInstrInfo::copyFromCPSR(MachineBasicBlock &MBB,
+ MachineBasicBlock::iterator I,
+ unsigned DestReg, bool KillSrc,
+ const ARMSubtarget &Subtarget) const {
+ unsigned Opc = Subtarget.isThumb()
+ ? (Subtarget.isMClass() ? ARM::t2MRS_M : ARM::t2MRS_AR)
+ : ARM::MRS;
+
+ MachineInstrBuilder MIB =
+ BuildMI(MBB, I, I->getDebugLoc(), get(Opc), DestReg);
+
+ // There is only 1 A/R class MRS instruction, and it always refers to
+ // APSR. However, there are lots of other possibilities on M-class cores.
+ if (Subtarget.isMClass())
+ MIB.addImm(0x800);
+
+ AddDefaultPred(MIB);
+
+ MIB.addReg(ARM::CPSR, RegState::Implicit | getKillRegState(KillSrc));
+}
+
+void ARMBaseInstrInfo::copyToCPSR(MachineBasicBlock &MBB,
+ MachineBasicBlock::iterator I,
+ unsigned SrcReg, bool KillSrc,
+ const ARMSubtarget &Subtarget) const {
+ unsigned Opc = Subtarget.isThumb()
+ ? (Subtarget.isMClass() ? ARM::t2MSR_M : ARM::t2MSR_AR)
+ : ARM::MSR;
+
+ MachineInstrBuilder MIB = BuildMI(MBB, I, I->getDebugLoc(), get(Opc));
+
+ if (Subtarget.isMClass())
+ MIB.addImm(0x800);
+ else
+ MIB.addImm(8);
+
+ MIB.addReg(SrcReg, getKillRegState(KillSrc));
+
+ AddDefaultPred(MIB);
+
+ MIB.addReg(ARM::CPSR, RegState::Implicit | RegState::Define);
+}
+
void ARMBaseInstrInfo::copyPhysReg(MachineBasicBlock &MBB,
MachineBasicBlock::iterator I, DebugLoc DL,
unsigned DestReg, unsigned SrcReg,
@@ -785,6 +828,12 @@ void ARMBaseInstrInfo::copyPhysReg(Machi
Opc = ARM::VMOVS;
BeginIdx = ARM::ssub_0;
SubRegs = 2;
+ } else if (SrcReg == ARM::CPSR) {
+ copyFromCPSR(MBB, I, DestReg, KillSrc, Subtarget);
+ return;
+ } else if (DestReg == ARM::CPSR) {
+ copyToCPSR(MBB, I, SrcReg, KillSrc, Subtarget);
+ return;
}
assert(Opc && "Impossible reg-to-reg copy");
Modified: llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.h?rev=218789&r1=218788&r2=218789&view=diff
==============================================================================
--- llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.h (original)
+++ llvm/trunk/lib/Target/ARM/ARMBaseInstrInfo.h Wed Oct 1 14:21:03 2014
@@ -156,6 +156,13 @@ public:
unsigned isStoreToStackSlotPostFE(const MachineInstr *MI,
int &FrameIndex) const override;
+ void copyToCPSR(MachineBasicBlock &MBB, MachineBasicBlock::iterator I,
+ unsigned SrcReg, bool KillSrc,
+ const ARMSubtarget &Subtarget) const;
+ void copyFromCPSR(MachineBasicBlock &MBB, MachineBasicBlock::iterator I,
+ unsigned DestReg, bool KillSrc,
+ const ARMSubtarget &Subtarget) const;
+
void copyPhysReg(MachineBasicBlock &MBB, MachineBasicBlock::iterator I,
DebugLoc DL, unsigned DestReg, unsigned SrcReg,
bool KillSrc) const override;
Modified: llvm/trunk/lib/Target/ARM/ARMBaseRegisterInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/ARMBaseRegisterInfo.cpp?rev=218789&r1=218788&r2=218789&view=diff
==============================================================================
--- llvm/trunk/lib/Target/ARM/ARMBaseRegisterInfo.cpp (original)
+++ llvm/trunk/lib/Target/ARM/ARMBaseRegisterInfo.cpp Wed Oct 1 14:21:03 2014
@@ -182,7 +182,7 @@ ARMBaseRegisterInfo::getPointerRegClass(
const TargetRegisterClass *
ARMBaseRegisterInfo::getCrossCopyRegClass(const TargetRegisterClass *RC) const {
if (RC == &ARM::CCRRegClass)
- return nullptr; // Can't copy CCR registers.
+ return &ARM::rGPRRegClass; // Can't copy CCR registers.
return RC;
}
Added: llvm/trunk/test/CodeGen/ARM/copy-cpsr.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/ARM/copy-cpsr.ll?rev=218789&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/ARM/copy-cpsr.ll (added)
+++ llvm/trunk/test/CodeGen/ARM/copy-cpsr.ll Wed Oct 1 14:21:03 2014
@@ -0,0 +1,41 @@
+; RUN: llc -mtriple=armv7s-apple-ios7.0 -show-mc-encoding %s -o - | FileCheck %s --check-prefix=CHECK-ARM
+; RUN: llc -mtriple=thumbv7s-apple-ios7.0 -show-mc-encoding %s -o - | FileCheck %s --check-prefix=CHECK-THUMB
+; RUN: llc -mtriple=thumbv7m-none-eabi -show-mc-encoding %s -o - | FileCheck %s --check-prefix=CHECK-THUMB
+
+; In the ARM backend, most compares are glued to their uses so CPSR can't
+; escape. However, for long ADCS chains (and last ditch fallback) the dependency
+; is carried in the DAG because duplicating them can be more expensive than
+; copying CPSR.
+
+; Crafting a test for this was a little tricky, in case it breaks here are some
+; notes on what I was tring to achieve:
+; + We want 2 long ADCS chains
+; + We want them to split after an initial common prefix (so that a single
+; CPSR is used twice).
+; + We want both chains to write CPSR post-split (so that the copy can't be
+; elided).
+; + We want the chains to be long enough that duplicating them is expensive.
+
+define void @test_copy_cpsr(i128 %lhs, i128 %rhs, i128* %addr) {
+; CHECK-ARM: test_copy_cpsr:
+; CHECK-THUMB: test_copy_cpsr:
+
+; CHECK-ARM: mrs [[TMP:r[0-9]+]], apsr @ encoding: [0x00,0x{{[0-9a-f]}}0,0x0f,0xe1]
+; CHECK-ARM: msr APSR_nzcvq, [[TMP]] @ encoding: [0x0{{[0-9a-f]}},0xf0,0x28,0xe1]
+
+ ; In Thumb mode v7M and v7AR have different MRS/MSR instructions that happen
+ ; to overlap for the apsr case, so it's definitely worth checking both.
+; CHECK-THUMB: mrs [[TMP:r[0-9]+]], apsr @ encoding: [0xef,0xf3,0x00,0x8{{[0-9a-f]}}]
+; CHECK-THUMB: msr {{APSR|apsr}}_nzcvq, [[TMP]] @ encoding: [0x8{{[0-9a-f]}},0xf3,0x00,0x88]
+
+ %sum = add i128 %lhs, %rhs
+ store volatile i128 %sum, i128* %addr
+
+ %rhs2.tmp1 = trunc i128 %rhs to i64
+ %rhs2 = zext i64 %rhs2.tmp1 to i128
+
+ %sum2 = add i128 %lhs, %rhs2
+ store volatile i128 %sum2, i128* %addr
+
+ ret void
+}
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