Revert "[AArch64] Allocate two emergency spill slots for MTE to fix register …" (#186900)

Reverts llvm/llvm-project#186505

Breaks buildbot

llvm/include/llvm/CodeGen/RegisterScavenging.h

@@ -129,8 +129,6 @@ public:
         A.push_back(I.FrameIndex);
   }
 
-  size_t getNumScavengingFrameIndices() const { return Scavenged.size(); }
-
   /// Make a register of the specific register class available from the current
   /// position backwards to the place before \p To. If \p RestoreAfter is true
   /// this includes the instruction following the current position.

llvm/lib/Target/AArch64/AArch64FrameLowering.cpp

@@ -3367,21 +3367,6 @@ bool isMergeableStackTaggingInstruction(MachineInstr &MI, int64_t &Offset,
   return true;
 }
 
-static size_t countAvailableScavengerSlots(LivePhysRegs &LiveRegs,
-                                           MachineRegisterInfo &MRI,
-                                           RegScavenger *RS) {
-  auto FreeGPRs =
-      llvm::count_if(AArch64::GPR64RegClass, [&LiveRegs, &MRI](auto Reg) {
-        return LiveRegs.available(MRI, Reg);
-      });
-
-  size_t NumEmergencySlots = 0;
-  if (RS)
-    NumEmergencySlots = RS->getNumScavengingFrameIndices();
-
-  return FreeGPRs + NumEmergencySlots;
-}
-
 // Detect a run of memory tagging instructions for adjacent stack frame slots,
 // and replace them with a shorter instruction sequence:
 // * replace STG + STG with ST2G
@@ -3461,19 +3446,6 @@ MachineBasicBlock::iterator tryMergeAdjacentSTG(MachineBasicBlock::iterator II,
   if (LiveRegs.contains(AArch64::NZCV))
     return InsertI;
 
-  // Emitting an MTE loop requires two physical registers (BaseReg and
-  // SizeReg).  If the function is under register pressure, the register
-  // scavenger will crash trying to allocate them. If we don't have at least
-  // two free slots (free registers + emergency slots), bail out and fall back
-  // to the unrolled sequence.
-  if (countAvailableScavengerSlots(LiveRegs, MBB->getParent()->getRegInfo(),
-                                   RS) < 2) {
-    LLVM_DEBUG(
-        dbgs() << "Failed to merge MTE stack tagging instructions into loop "
-               << "due to high register pressure.\n");
-    return InsertI;
-  }
-
   llvm::stable_sort(Instrs,
                     [](const TagStoreInstr &Left, const TagStoreInstr &Right) {
                       return Left.Offset < Right.Offset;

llvm/test/CodeGen/AArch64/memtag-stg-loop-reg-pressure.mir

@@ -1,190 +0,0 @@
-# RUN: llc -mtriple=aarch64 -mattr=+mte -run-pass=prologepilog %s -o - | FileCheck %s
-
-# This test ensures that when register pressure is extremely high, the compiler
-# does not attempt to merge ST2Gi instructions into an STGloop. STGloop requires
-# two scratch locations (either free GPRs or emergency spill slots) which the
-# scavenger cannot provide without crashing.
-#
-# We test the 4 possible combinations of (Free GPRs) + (Emergency Spill Slots)
-# to ensure the loop is only formed when the sum is >= 2.
-#
-# CHECK-LABEL: name: test_zero_csr_zero_caller
-# CHECK-NOT: STGloop
-# CHECK-LABEL: name: test_one_csr_zero_caller
-# CHECK-NOT: STGloop
-# CHECK-LABEL: name: test_one_csr_one_caller
-# CHECK: STGloop
-# CHECK-LABEL: name: test_zero_csr_one_caller
-# CHECK: STGloop
-
---- |
-  define void @test_zero_csr_zero_caller() {
-  entry:
-    ret void
-  }
-  define void @test_one_csr_zero_caller() {
-  entry:
-    ret void
-  }
-  define void @test_one_csr_one_caller() {
-  entry:
-    ret void
-  }
-  define void @test_zero_csr_one_caller() {
-  entry:
-    ret void
-  }
-...
----
-name:            test_zero_csr_zero_caller
-tracksRegLiveness: true
-calleeSavedRegisters: [ '$fp', '$lr', '$x19', '$x20', '$x21', '$x22', '$x23', '$x24', '$x25', '$x26', '$x27', '$x28' ]
-stack:
-  - { id: 0, size: 8192, alignment: 16 }
-  - { id: 1, size: 32, alignment: 16 }
-  - { id: 2, size: 32, alignment: 16 }
-  - { id: 3, size: 32, alignment: 16 }
-  - { id: 4, size: 32, alignment: 16 }
-  - { id: 5, size: 32, alignment: 16 }
-  - { id: 6, size: 32, alignment: 16 }
-  - { id: 7, size: 32, alignment: 16 }
-  - { id: 8, size: 32, alignment: 16 }
-  - { id: 9, size: 32, alignment: 16 }
-  - { id: 10, size: 32, alignment: 16 }
-body:             |
-  bb.0.entry:
-    liveins: $x0, $x1, $x2, $x3, $x4, $x5, $x6, $x7, $x8, $x9, $x10, $x11, $x12, $x13, $x14, $x15, $x16, $x17, $x18, $x19, $x20, $x21, $x22, $x23, $x24, $x25, $x26, $x27, $x28, $fp, $lr
-    ; STG loop trigger
-    ST2Gi $sp, %stack.1, 0 :: (store (s256))
-    ST2Gi $sp, %stack.2, 0 :: (store (s256))
-    ST2Gi $sp, %stack.3, 0 :: (store (s256))
-    ST2Gi $sp, %stack.4, 0 :: (store (s256))
-    ST2Gi $sp, %stack.5, 0 :: (store (s256))
-    ST2Gi $sp, %stack.6, 0 :: (store (s256))
-    ST2Gi $sp, %stack.7, 0 :: (store (s256))
-    ST2Gi $sp, %stack.8, 0 :: (store (s256))
-    ST2Gi $sp, %stack.9, 0 :: (store (s256))
-    ST2Gi $sp, %stack.10, 0 :: (store (s256))
-
-    ; Explicitly use them on the RET instruction so they are kept alive across the ST2Gi.
-    KILL implicit $x0, implicit $x1, implicit $x2, implicit $x3, implicit $x4, implicit $x5, implicit $x6, implicit $x7, implicit $x8, implicit $x9, implicit $x10, implicit $x11, implicit $x12, implicit $x13, implicit $x14, implicit $x15, implicit $x16, implicit $x17, implicit $x18, implicit $x19, implicit $x20, implicit $x21, implicit $x22, implicit $x23, implicit $x24, implicit $x25, implicit $x26, implicit $x27, implicit $x28, implicit $fp, implicit $lr
-    RET_ReallyLR
-...
----
-name:            test_one_csr_zero_caller
-alignment:       4
-tracksRegLiveness: true
-calleeSavedRegisters: [ '$fp', '$lr', '$x19', '$x20', '$x21', '$x22', '$x23', '$x24', '$x25', '$x26', '$x27', '$x28' ]
-frameInfo:
-  maxAlignment:    16
-stack:
-  - { id: 0, size: 8192, alignment: 16 }
-  - { id: 1, size: 32, alignment: 16 }
-  - { id: 2, size: 32, alignment: 16 }
-  - { id: 3, size: 32, alignment: 16 }
-  - { id: 4, size: 32, alignment: 16 }
-  - { id: 5, size: 32, alignment: 16 }
-  - { id: 6, size: 32, alignment: 16 }
-  - { id: 7, size: 32, alignment: 16 }
-  - { id: 8, size: 32, alignment: 16 }
-  - { id: 9, size: 32, alignment: 16 }
-  - { id: 10, size: 32, alignment: 16 }
-body:             |
-  bb.0.entry:
-    ; Intentionally omitting $x28 from liveins and the RET instruction to use as scratch register
-    liveins: $x0, $x1, $x2, $x3, $x4, $x5, $x6, $x7, $x8, $x9, $x10, $x11, $x12, $x13, $x14, $x15, $x16, $x17, $x18, $x19, $x20, $x21, $x22, $x23, $x24, $x25, $x26, $x27, $fp, $lr
-
-    ST2Gi $sp, %stack.1, 0 :: (store (s256))
-    ST2Gi $sp, %stack.2, 0 :: (store (s256))
-    ST2Gi $sp, %stack.3, 0 :: (store (s256))
-    ST2Gi $sp, %stack.4, 0 :: (store (s256))
-    ST2Gi $sp, %stack.5, 0 :: (store (s256))
-    ST2Gi $sp, %stack.6, 0 :: (store (s256))
-    ST2Gi $sp, %stack.7, 0 :: (store (s256))
-    ST2Gi $sp, %stack.8, 0 :: (store (s256))
-    ST2Gi $sp, %stack.9, 0 :: (store (s256))
-    ST2Gi $sp, %stack.10, 0 :: (store (s256))
-
-    KILL implicit $x0, implicit $x1, implicit $x2, implicit $x3, implicit $x4, implicit $x5, implicit $x6, implicit $x7, implicit $x8, implicit $x9, implicit $x10, implicit $x11, implicit $x12, implicit $x13, implicit $x14, implicit $x15, implicit $x16, implicit $x17, implicit $x18, implicit $x19, implicit $x20, implicit $x21, implicit $x22, implicit $x23, implicit $x24, implicit $x25, implicit $x26, implicit $x27, implicit $fp, implicit $lr
-    RET_ReallyLR
-...
----
-name:            test_one_csr_one_caller
-alignment:       4
-tracksRegLiveness: true
-calleeSavedRegisters: [ '$fp', '$lr', '$x19', '$x20', '$x21', '$x22', '$x23', '$x24', '$x25', '$x26', '$x27', '$x28' ]
-frameInfo:
-  maxAlignment:    16
-stack:
-  - { id: 0, size: 8192, alignment: 16 }
-  - { id: 1, size: 32, alignment: 16 }
-  - { id: 2, size: 32, alignment: 16 }
-  - { id: 3, size: 32, alignment: 16 }
-  - { id: 4, size: 32, alignment: 16 }
-  - { id: 5, size: 32, alignment: 16 }
-  - { id: 6, size: 32, alignment: 16 }
-  - { id: 7, size: 32, alignment: 16 }
-  - { id: 8, size: 32, alignment: 16 }
-  - { id: 9, size: 32, alignment: 16 }
-  - { id: 10, size: 32, alignment: 16 }
-body:             |
-  bb.0.entry:
-    ; Intentionally omitting:
-    ; $x28 (csr) to be used as scratch register
-    ; $x0 (caller saved) to be scavenged
-    liveins: $x1, $x2, $x3, $x4, $x5, $x6, $x7, $x8, $x9, $x10, $x11, $x12, $x13, $x14, $x15, $x16, $x17, $x18, $x19, $x20, $x21, $x22, $x23, $x24, $x25, $x26, $x27, $fp, $lr
-
-    ST2Gi $sp, %stack.1, 0 :: (store (s256))
-    ST2Gi $sp, %stack.2, 0 :: (store (s256))
-    ST2Gi $sp, %stack.3, 0 :: (store (s256))
-    ST2Gi $sp, %stack.4, 0 :: (store (s256))
-    ST2Gi $sp, %stack.5, 0 :: (store (s256))
-    ST2Gi $sp, %stack.6, 0 :: (store (s256))
-    ST2Gi $sp, %stack.7, 0 :: (store (s256))
-    ST2Gi $sp, %stack.8, 0 :: (store (s256))
-    ST2Gi $sp, %stack.9, 0 :: (store (s256))
-    ST2Gi $sp, %stack.10, 0 :: (store (s256))
-
-    KILL implicit $x1, implicit $x2, implicit $x3, implicit $x4, implicit $x5, implicit $x6, implicit $x7, implicit $x8, implicit $x9, implicit $x10, implicit $x11, implicit $x12, implicit $x13, implicit $x14, implicit $x15, implicit $x16, implicit $x17, implicit $x18, implicit $x19, implicit $x20, implicit $x21, implicit $x22, implicit $x23, implicit $x24, implicit $x25, implicit $x26, implicit $x27, implicit $fp, implicit $lr
-    RET_ReallyLR
-...
----
-name:            test_zero_csr_one_caller
-alignment:       4
-tracksRegLiveness: true
-calleeSavedRegisters: [ '$fp', '$lr', '$x19', '$x20', '$x21', '$x22', '$x23', '$x24', '$x25', '$x26', '$x27', '$x28' ]
-frameInfo:
-  maxAlignment:    16
-stack:
-  - { id: 0, size: 8192, alignment: 16 }
-  - { id: 1, size: 32, alignment: 16 }
-  - { id: 2, size: 32, alignment: 16 }
-  - { id: 3, size: 32, alignment: 16 }
-  - { id: 4, size: 32, alignment: 16 }
-  - { id: 5, size: 32, alignment: 16 }
-  - { id: 6, size: 32, alignment: 16 }
-  - { id: 7, size: 32, alignment: 16 }
-  - { id: 8, size: 32, alignment: 16 }
-  - { id: 9, size: 32, alignment: 16 }
-  - { id: 10, size: 32, alignment: 16 }
-body:             |
-  bb.0.entry:
-    ; Intentionally omitting:
-    ; No CSRs: determineCalleeSaves allocates a spill slot
-    ; $x0 (caller saved) to be scavenged
-    liveins: $x1, $x2, $x3, $x4, $x5, $x6, $x7, $x8, $x9, $x10, $x11, $x12, $x13, $x14, $x15, $x16, $x17, $x18, $x19, $x20, $x21, $x22, $x23, $x24, $x25, $x26, $x27, $x28, $fp, $lr
-
-    ST2Gi $sp, %stack.1, 0 :: (store (s256))
-    ST2Gi $sp, %stack.2, 0 :: (store (s256))
-    ST2Gi $sp, %stack.3, 0 :: (store (s256))
-    ST2Gi $sp, %stack.4, 0 :: (store (s256))
-    ST2Gi $sp, %stack.5, 0 :: (store (s256))
-    ST2Gi $sp, %stack.6, 0 :: (store (s256))
-    ST2Gi $sp, %stack.7, 0 :: (store (s256))
-    ST2Gi $sp, %stack.8, 0 :: (store (s256))
-    ST2Gi $sp, %stack.9, 0 :: (store (s256))
-    ST2Gi $sp, %stack.10, 0 :: (store (s256))
-
-    KILL implicit $x1, implicit $x2, implicit $x3, implicit $x4, implicit $x5, implicit $x6, implicit $x7, implicit $x8, implicit $x9, implicit $x10, implicit $x11, implicit $x12, implicit $x13, implicit $x14, implicit $x15, implicit $x16, implicit $x17, implicit $x18, implicit $x19, implicit $x20, implicit $x21, implicit $x22, implicit $x23, implicit $x24, implicit $x25, implicit $x26, implicit $x27, implicit $x28, implicit $fp, implicit $lr
-    RET_ReallyLR
-...