[TII] Do not fold undef copies

llvm/lib/CodeGen/TargetInstrInfo.cpp

@@ -772,12 +772,18 @@ MachineInstr *TargetInstrInfo::foldMemoryOperand(MachineInstr &MI,
 
   const MachineOperand &MO = MI.getOperand(1 - Ops[0]);
   MachineBasicBlock::iterator Pos = MI;
-
-  if (Flags == MachineMemOperand::MOStore)
-    storeRegToStackSlot(*MBB, Pos, MO.getReg(), MO.isKill(), FI, RC, TRI,
-                        Register());
-  else
+  if (Flags == MachineMemOperand::MOStore) {
+    if (MO.isUndef()) {
+      // If this is an undef copy, we do not need to bother we inserting spill
+      // code.
+      BuildMI(*MBB, Pos, MI.getDebugLoc(), get(TargetOpcode::KILL)).add(MO);
+    } else {
+      storeRegToStackSlot(*MBB, Pos, MO.getReg(), MO.isKill(), FI, RC, TRI,
+                          Register());
+    }
+  } else
     loadRegFromStackSlot(*MBB, Pos, MO.getReg(), FI, RC, TRI, Register());
+
   return &*--Pos;
 }
 

llvm/test/CodeGen/AMDGPU/regalloc-undef-copy-fold.mir

@@ -0,0 +1,79 @@
+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 5
+# RUN: llc -mtriple=amdgcn -mcpu=gfx908 -verify-machineinstrs --start-before=greedy,2 --stop-after=greedy,2 %s -o - | FileCheck %s
+
+# Make sure there's no machine verifier error
+
+# If RA is unable to find a register to allocate, then cleanupFailedVReg will do ad-hoc rewriting and will insert undefs to make the LiveRanges workable.
+# %30:av_128 = COPY undef $vgpr0_vgpr1_vgpr2_vgpr3 is an example of such a rewrite / undef. If we were to want to spill %30, we should not be inserting
+# actual spill code, as the source operand is undef.
+# Check that there are no verfier issues with the LiveRange of $vgpr0_vgpr1_vgpr2_vgpr3 / that we do not insert spill code for %30.
+
+
+--- |
+  define void @foo() #0 {
+    ret void
+  }
+
+  attributes #0 = { "amdgpu-waves-per-eu"="8,8" }
+
+...
+
+---
+name:            foo
+tracksRegLiveness: true
+stack:
+  - { id: 0, type: spill-slot, size: 32, alignment: 4 }
+machineFunctionInfo:
+  maxKernArgAlign: 4
+  isEntryFunction: true
+  waveLimiter:     true
+  scratchRSrcReg:  '$sgpr96_sgpr97_sgpr98_sgpr99'
+  stackPtrOffsetReg: '$sgpr32'
+  frameOffsetReg: '$sgpr33'
+  hasSpilledVGPRs: true
+  argumentInfo:
+    privateSegmentBuffer: { reg: '$sgpr0_sgpr1_sgpr2_sgpr3' }
+    dispatchPtr:     { reg: '$sgpr4_sgpr5' }
+    kernargSegmentPtr: { reg: '$sgpr6_sgpr7' }
+    workGroupIDX:    { reg: '$sgpr8' }
+    privateSegmentWaveByteOffset: { reg: '$sgpr9' }
+body:             |
+  bb.0:
+    ; CHECK-LABEL: name: foo
+    ; CHECK: INLINEASM &"; def $0 $1 $2 $3 $4", 1 /* sideeffect attdialect */, 10 /* regdef */, def %10, 10 /* regdef */, def %1, 10 /* regdef */, def %2, 10 /* regdef */, def $vgpr0_vgpr1_vgpr2_vgpr3, 10 /* regdef */, implicit-def $agpr0_agpr1_agpr2_agpr3_agpr4_agpr5_agpr6_agpr7_agpr8_agpr9_agpr10_agpr11_agpr12_agpr13_agpr14_agpr15
+    ; CHECK-NEXT: KILL undef $vgpr0_vgpr1_vgpr2_vgpr3
+    ; CHECK-NEXT: SI_SPILL_AV160_SAVE %2, %stack.1, $sgpr32, 0, implicit $exec :: (store (s160) into %stack.1, align 4, addrspace 5)
+    ; CHECK-NEXT: SI_SPILL_AV256_SAVE %1, %stack.3, $sgpr32, 0, implicit $exec :: (store (s256) into %stack.3, align 4, addrspace 5)
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:vreg_512 = COPY %10
+    ; CHECK-NEXT: SI_SPILL_V512_SAVE [[COPY]], %stack.0, $sgpr32, 0, implicit $exec :: (store (s512) into %stack.0, align 4, addrspace 5)
+    ; CHECK-NEXT: [[COPY1:%[0-9]+]]:vreg_512 = COPY $agpr0_agpr1_agpr2_agpr3_agpr4_agpr5_agpr6_agpr7_agpr8_agpr9_agpr10_agpr11_agpr12_agpr13_agpr14_agpr15
+    ; CHECK-NEXT: SI_SPILL_V512_SAVE [[COPY1]], %stack.6, $sgpr32, 0, implicit $exec :: (store (s512) into %stack.6, align 4, addrspace 5)
+    ; CHECK-NEXT: INLINEASM &"; clobber", 1 /* sideeffect attdialect */, 10 /* regdef */, implicit-def early-clobber $vgpr0_vgpr1_vgpr2_vgpr3_vgpr4_vgpr5_vgpr6_vgpr7_vgpr8_vgpr9_vgpr10_vgpr11_vgpr12_vgpr13_vgpr14_vgpr15_vgpr16_vgpr17_vgpr18_vgpr19_vgpr20_vgpr21_vgpr22_vgpr23_vgpr24_vgpr25_vgpr26_vgpr27_vgpr28_vgpr29_vgpr30_vgpr31
+    ; CHECK-NEXT: [[SI_SPILL_V512_RESTORE:%[0-9]+]]:vreg_512 = SI_SPILL_V512_RESTORE %stack.6, $sgpr32, 0, implicit $exec :: (load (s512) from %stack.6, align 4, addrspace 5)
+    ; CHECK-NEXT: $agpr1_agpr2_agpr3_agpr4_agpr5_agpr6_agpr7_agpr8_agpr9_agpr10_agpr11_agpr12_agpr13_agpr14_agpr15_agpr16 = COPY [[SI_SPILL_V512_RESTORE]]
+    ; CHECK-NEXT: [[SI_SPILL_V512_RESTORE1:%[0-9]+]]:vreg_512 = SI_SPILL_V512_RESTORE %stack.0, $sgpr32, 0, implicit $exec :: (load (s512) from %stack.0, align 4, addrspace 5)
+    ; CHECK-NEXT: SI_SPILL_V512_SAVE [[SI_SPILL_V512_RESTORE1]], %stack.4, $sgpr32, 0, implicit $exec :: (store (s512) into %stack.4, align 4, addrspace 5)
+    ; CHECK-NEXT: [[SI_SPILL_AV256_RESTORE:%[0-9]+]]:vreg_256 = SI_SPILL_AV256_RESTORE %stack.3, $sgpr32, 0, implicit $exec :: (load (s256) from %stack.3, align 4, addrspace 5)
+    ; CHECK-NEXT: SI_SPILL_V256_SAVE [[SI_SPILL_AV256_RESTORE]], %stack.5, $sgpr32, 0, implicit $exec :: (store (s256) into %stack.5, align 4, addrspace 5)
+    ; CHECK-NEXT: [[SI_SPILL_AV160_RESTORE:%[0-9]+]]:vreg_160 = SI_SPILL_AV160_RESTORE %stack.1, $sgpr32, 0, implicit $exec :: (load (s160) from %stack.1, align 4, addrspace 5)
+    ; CHECK-NEXT: $vgpr0_vgpr1_vgpr2_vgpr3 = SI_SPILL_AV128_RESTORE %stack.2, $sgpr32, 0, implicit $exec :: (load (s128) from %stack.2, align 4, addrspace 5)
+    ; CHECK-NEXT: [[SI_SPILL_AV512_RESTORE:%[0-9]+]]:av_512 = SI_SPILL_AV512_RESTORE %stack.4, $sgpr32, 0, implicit $exec :: (load (s512) from %stack.4, align 4, addrspace 5)
+    ; CHECK-NEXT: [[SI_SPILL_V256_RESTORE:%[0-9]+]]:vreg_256 = SI_SPILL_V256_RESTORE %stack.5, $sgpr32, 0, implicit $exec :: (load (s256) from %stack.5, align 4, addrspace 5)
+    ; CHECK-NEXT: INLINEASM &"; use $0 $1 $2 $3 $4", 1 /* sideeffect attdialect */, 9 /* reguse */, [[SI_SPILL_AV512_RESTORE]], 9 /* reguse */, [[SI_SPILL_V256_RESTORE]], 9 /* reguse */, [[SI_SPILL_AV160_RESTORE]], 9 /* reguse */, undef $vgpr0_vgpr1_vgpr2_vgpr3, 9 /* reguse */, $agpr1_agpr2_agpr3_agpr4_agpr5_agpr6_agpr7_agpr8_agpr9_agpr10_agpr11_agpr12_agpr13_agpr14_agpr15_agpr16
+    ; CHECK-NEXT: SI_RETURN
+    INLINEASM &"; def $0 $1 $2 $3 $4", 1 /* sideeffect attdialect */, 10, def %22:vreg_512, 10, def %25:vreg_256, 10, def %28:vreg_160, 10, def $vgpr0_vgpr1_vgpr2_vgpr3, 10, implicit-def $agpr0_agpr1_agpr2_agpr3_agpr4_agpr5_agpr6_agpr7_agpr8_agpr9_agpr10_agpr11_agpr12_agpr13_agpr14_agpr15
+    %30:av_128 = COPY undef $vgpr0_vgpr1_vgpr2_vgpr3
+    %27:av_160 = COPY %28:vreg_160
+    %24:av_256 = COPY %25:vreg_256
+    SI_SPILL_V512_SAVE %22:vreg_512, %stack.0, $sgpr32, 0, implicit $exec :: (store (s512) into %stack.0, align 4, addrspace 5)
+    %18:vreg_512 = COPY $agpr0_agpr1_agpr2_agpr3_agpr4_agpr5_agpr6_agpr7_agpr8_agpr9_agpr10_agpr11_agpr12_agpr13_agpr14_agpr15
+    INLINEASM &"; clobber", 1 /* sideeffect attdialect */, 10, implicit-def early-clobber $vgpr0_vgpr1_vgpr2_vgpr3_vgpr4_vgpr5_vgpr6_vgpr7_vgpr8_vgpr9_vgpr10_vgpr11_vgpr12_vgpr13_vgpr14_vgpr15_vgpr16_vgpr17_vgpr18_vgpr19_vgpr20_vgpr21_vgpr22_vgpr23_vgpr24_vgpr25_vgpr26_vgpr27_vgpr28_vgpr29_vgpr30_vgpr31
+    $agpr1_agpr2_agpr3_agpr4_agpr5_agpr6_agpr7_agpr8_agpr9_agpr10_agpr11_agpr12_agpr13_agpr14_agpr15_agpr16 = COPY %18:vreg_512
+    %23:vreg_512 = SI_SPILL_V512_RESTORE %stack.0, $sgpr32, 0, implicit $exec :: (load (s512) from %stack.0, align 4, addrspace 5)
+    %26:vreg_256 = COPY %24:av_256
+    %29:vreg_160 = COPY %27:av_160
+    $vgpr0_vgpr1_vgpr2_vgpr3 = COPY %30:av_128
+    INLINEASM &"; use $0 $1 $2 $3 $4", 1 /* sideeffect attdialect */, 9, %23:vreg_512, 9, %26:vreg_256, 9, %29:vreg_160, 9, undef $vgpr0_vgpr1_vgpr2_vgpr3, 9, $agpr1_agpr2_agpr3_agpr4_agpr5_agpr6_agpr7_agpr8_agpr9_agpr10_agpr11_agpr12_agpr13_agpr14_agpr15_agpr16
+    SI_RETURN
+
+...