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RegisterCoalescer: Fix producing malformed IMPLICIT_DEFs (#73784)
If this was coalescing a SUBREG_TO_REG as a copy, the resulting instruction would be an IMPLICIT_DEF with an unexpected 2 immediate operands, which need to be dropped. Until recently the verifier did not catch this error, and an assert would fire if later the broken IMPLICIT_DEF was rematerialized P #73758 is related, it changes the failure mode to a verifier error.
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‎llvm/lib/CodeGen/RegisterCoalescer.cpp

Lines changed: 9 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1694,12 +1694,19 @@ MachineInstr *RegisterCoalescer::eliminateUndefCopy(MachineInstr *CopyMI) {
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// The source interval may also have been on an undef use, in which case the
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// copy introduced a live value.
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if (((V && V->isPHIDef()) || (!V && !DstLI.liveAt(Idx)))) {
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CopyMI->setDesc(TII->get(TargetOpcode::IMPLICIT_DEF));
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for (unsigned i = CopyMI->getNumOperands(); i != 0; --i) {
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MachineOperand &MO = CopyMI->getOperand(i-1);
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if (MO.isReg() && MO.isUse())
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if (MO.isReg()) {
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if (MO.isUse())
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CopyMI->removeOperand(i - 1);
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} else {
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assert(MO.isImm() &&
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CopyMI->getOpcode() == TargetOpcode::SUBREG_TO_REG);
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CopyMI->removeOperand(i-1);
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}
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}
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CopyMI->setDesc(TII->get(TargetOpcode::IMPLICIT_DEF));
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LLVM_DEBUG(dbgs() << "\tReplaced copy of <undef> value with an "
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"implicit def\n");
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return CopyMI;

‎llvm/test/CodeGen/AArch64/coalescer-drop-subreg-to-reg-imm-ops.mir

Lines changed: 120 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,120 @@
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# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 4
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# RUN: llc -mtriple=arm64-apple-macosx -mcpu=apple-m1 -verify-coalescing -run-pass=register-coalescer -o - %s | FileCheck %s
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# Hits assert "Trying to add an operand to a machine instr that is
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# already done!" when rematerializing during greedy. This was because
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# an IMPLICIT_DEF ended up with some immediate operands during
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# coalescing. A SUBREG_TO_REG was not dropping the immediate operands
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# when mutating to IMPLICIT_DEF, and would later fail the assert when
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# creating a new IMPLICIT_DEF copy during rematerialization.
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--- |
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define void @_ZN38SanitizerCommonInterceptors_Scanf_Test8TestBodyEv() {
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ret void
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}
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declare void @_ZL9testScanfPKcjz(ptr, i32, ...)
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...
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---
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name: _ZN38SanitizerCommonInterceptors_Scanf_Test8TestBodyEv
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alignment: 4
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tracksRegLiveness: true
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frameInfo:
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maxAlignment: 8
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adjustsStack: true
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hasCalls: true
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maxCallFrameSize: 24
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body: |
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bb.0:
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liveins: $x0, $x1, $x2, $x3, $x4, $x5, $x6
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; CHECK-LABEL: name: _ZN38SanitizerCommonInterceptors_Scanf_Test8TestBodyEv
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; CHECK: liveins: $x0, $x1, $x2, $x3, $x4, $x5, $x6
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; CHECK-NEXT: {{ $}}
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; CHECK-NEXT: [[DEF:%[0-9]+]]:gpr64sp = IMPLICIT_DEF
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; CHECK-NEXT: dead [[DEF1:%[0-9]+]]:gpr32 = IMPLICIT_DEF
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; CHECK-NEXT: [[DEF2:%[0-9]+]]:gpr64common = IMPLICIT_DEF
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; CHECK-NEXT: [[COPY:%[0-9]+]]:gpr64 = COPY $x5
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; CHECK-NEXT: [[COPY1:%[0-9]+]]:gpr64 = COPY $x4
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; CHECK-NEXT: [[COPY2:%[0-9]+]]:gpr64 = COPY $x3
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; CHECK-NEXT: [[COPY3:%[0-9]+]]:gpr64 = COPY $x2
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; CHECK-NEXT: [[COPY4:%[0-9]+]]:gpr64 = COPY $x1
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; CHECK-NEXT: [[COPY5:%[0-9]+]]:gpr64 = COPY $x0
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; CHECK-NEXT: [[DEF3:%[0-9]+]]:gpr64 = IMPLICIT_DEF
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; CHECK-NEXT: [[DEF4:%[0-9]+]]:gpr64 = IMPLICIT_DEF
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; CHECK-NEXT: [[DEF5:%[0-9]+]]:gpr64 = IMPLICIT_DEF
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; CHECK-NEXT: ADJCALLSTACKDOWN 16, 0, implicit-def dead $sp, implicit $sp
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; CHECK-NEXT: BL @_ZL9testScanfPKcjz, csr_darwin_aarch64_aapcs, implicit-def dead $lr, implicit $sp, implicit-def $sp
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; CHECK-NEXT: ADJCALLSTACKUP 16, 0, implicit-def dead $sp, implicit $sp
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; CHECK-NEXT: ADJCALLSTACKDOWN 8, 0, implicit-def dead $sp, implicit $sp
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; CHECK-NEXT: STRXui [[DEF3]], [[DEF]], 0 :: (store (s64) into stack)
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; CHECK-NEXT: ADJCALLSTACKUP 8, 0, implicit-def dead $sp, implicit $sp
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; CHECK-NEXT: STRWui undef [[DEF1]], [[DEF2]], 0 :: (store (s32))
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; CHECK-NEXT: ADJCALLSTACKDOWN 8, 0, implicit-def dead $sp, implicit $sp
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; CHECK-NEXT: STRXui [[DEF4]], undef [[DEF]], 0 :: (store (s64) into stack)
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; CHECK-NEXT: $x0 = COPY [[COPY5]]
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; CHECK-NEXT: ADJCALLSTACKUP 8, 0, implicit-def dead $sp, implicit $sp
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; CHECK-NEXT: ADJCALLSTACKDOWN 8, 0, implicit-def dead $sp, implicit $sp
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; CHECK-NEXT: $x0 = COPY [[COPY4]]
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; CHECK-NEXT: ADJCALLSTACKUP 8, 0, implicit-def dead $sp, implicit $sp
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; CHECK-NEXT: ADJCALLSTACKDOWN 8, 0, implicit-def dead $sp, implicit $sp
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; CHECK-NEXT: $x0 = COPY [[COPY3]]
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; CHECK-NEXT: ADJCALLSTACKUP 8, 0, implicit-def dead $sp, implicit $sp
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; CHECK-NEXT: ADJCALLSTACKDOWN 8, 0, implicit-def dead $sp, implicit $sp
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; CHECK-NEXT: $x0 = COPY [[COPY2]]
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; CHECK-NEXT: ADJCALLSTACKUP 8, 0, implicit-def dead $sp, implicit $sp
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; CHECK-NEXT: ADJCALLSTACKDOWN 8, 0, implicit-def dead $sp, implicit $sp
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; CHECK-NEXT: $x0 = COPY [[COPY1]]
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; CHECK-NEXT: ADJCALLSTACKUP 8, 0, implicit-def dead $sp, implicit $sp
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; CHECK-NEXT: ADJCALLSTACKDOWN 8, 0, implicit-def dead $sp, implicit $sp
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; CHECK-NEXT: $x0 = COPY [[COPY]]
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; CHECK-NEXT: ADJCALLSTACKUP 8, 0, implicit-def dead $sp, implicit $sp
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; CHECK-NEXT: ADJCALLSTACKDOWN 24, 0, implicit-def dead $sp, implicit $sp
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; CHECK-NEXT: STRXui [[DEF5]], undef [[DEF]], 1 :: (store (s64) into stack + 8)
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; CHECK-NEXT: ADJCALLSTACKUP 24, 0, implicit-def dead $sp, implicit $sp
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; CHECK-NEXT: RET_ReallyLR
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%0:gpr64sp = IMPLICIT_DEF
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%1:gpr32 = IMPLICIT_DEF
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%2:gpr64common = IMPLICIT_DEF
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%3:gpr64 = COPY killed $x5
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%4:gpr64 = COPY killed $x4
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%5:gpr64 = COPY killed $x3
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%6:gpr64 = COPY killed $x2
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%7:gpr64 = COPY killed $x1
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%8:gpr64 = COPY killed $x0
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%9:gpr64 = IMPLICIT_DEF
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%10:gpr64 = IMPLICIT_DEF
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%11:gpr64 = SUBREG_TO_REG 0, killed undef %1, %subreg.sub_32
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ADJCALLSTACKDOWN 16, 0, implicit-def dead $sp, implicit $sp
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BL @_ZL9testScanfPKcjz, csr_darwin_aarch64_aapcs, implicit-def dead $lr, implicit $sp, implicit-def $sp
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ADJCALLSTACKUP 16, 0, implicit-def dead $sp, implicit $sp
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ADJCALLSTACKDOWN 8, 0, implicit-def dead $sp, implicit $sp
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STRXui %9, killed %0, 0 :: (store (s64) into stack)
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ADJCALLSTACKUP 8, 0, implicit-def dead $sp, implicit $sp
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STRWui undef %1, killed %2, 0 :: (store (s32))
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ADJCALLSTACKDOWN 8, 0, implicit-def dead $sp, implicit $sp
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STRXui killed %10, killed undef %0, 0 :: (store (s64) into stack)
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$x0 = COPY killed %8
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ADJCALLSTACKUP 8, 0, implicit-def dead $sp, implicit $sp
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ADJCALLSTACKDOWN 8, 0, implicit-def dead $sp, implicit $sp
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$x0 = COPY killed %7
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ADJCALLSTACKUP 8, 0, implicit-def dead $sp, implicit $sp
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ADJCALLSTACKDOWN 8, 0, implicit-def dead $sp, implicit $sp
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$x0 = COPY killed %6
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ADJCALLSTACKUP 8, 0, implicit-def dead $sp, implicit $sp
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ADJCALLSTACKDOWN 8, 0, implicit-def dead $sp, implicit $sp
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$x0 = COPY killed %5
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ADJCALLSTACKUP 8, 0, implicit-def dead $sp, implicit $sp
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ADJCALLSTACKDOWN 8, 0, implicit-def dead $sp, implicit $sp
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$x0 = COPY killed %4
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ADJCALLSTACKUP 8, 0, implicit-def dead $sp, implicit $sp
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ADJCALLSTACKDOWN 8, 0, implicit-def dead $sp, implicit $sp
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$x0 = COPY killed %3
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ADJCALLSTACKUP 8, 0, implicit-def dead $sp, implicit $sp
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ADJCALLSTACKDOWN 24, 0, implicit-def dead $sp, implicit $sp
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STRXui killed %11, undef %0, 1 :: (store (s64) into stack + 8)
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ADJCALLSTACKUP 24, 0, implicit-def dead $sp, implicit $sp
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RET_ReallyLR
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...

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