Index: lib/CodeGen/RegisterCoalescer.cpp =================================================================== --- lib/CodeGen/RegisterCoalescer.cpp +++ lib/CodeGen/RegisterCoalescer.cpp @@ -244,6 +244,14 @@ /// Return true if a copy involving a physreg should be joined. bool canJoinPhys(const CoalescerPair &CP); + /// When merging SrcReg and DstReg together, and the operand of the + /// specified DBG_VALUE refers to one of them, would the def that a + /// DBG_VALUE refers to change? This can happen when the DBG_VALUEs + /// operand is dead and it's merged into a different live value, + /// meaning the DBG_VALUE operands must be updated. + bool mergingChangesDbgValue(MachineInstr *DbgV, unsigned SrcReg, + unsigned DstReg) const; + /// Replace all defs and uses of SrcReg to DstReg and update the subregister /// number if it is not zero. If DstReg is a physical register and the /// existing subregister number of the def / use being updated is not zero, @@ -1617,6 +1625,58 @@ } } +bool RegisterCoalescer::mergingChangesDbgValue(MachineInstr *DbgV, + unsigned SrcReg, + unsigned DstReg) const { + assert(DbgV->isDebugValue()); + assert(DbgV->getParent() && "DbgValue with no parent"); + assert(DbgV->getOperand(0).isReg()); + unsigned DbgReg = DbgV->getOperand(0).getReg(); + + SlotIndex MIIdx = LIS->getSlotIndexes()->getIndexAfter(*DbgV); + const LiveInterval &SrcLI = LIS->getInterval(SrcReg); + + // Is the src reg live across the DBG_VALUE? + bool SrcLive = false; + auto LII = SrcLI.find(MIIdx); + if (LII != SrcLI.end() && LII->contains(MIIdx)) + SrcLive = true; + + bool DstLive = false; + // Destination register can be physical or virtual. + if (TargetRegisterInfo::isVirtualRegister(DstReg)) { + // Is DstReg live across the DBG_VALUE? + const LiveInterval &DstLI = LIS->getInterval(DstReg); + LII = DstLI.find(MIIdx); + DstLive = (LII != DstLI.end() && LII->contains(MIIdx)); + } else if (MRI->isConstantPhysReg(DstReg)) { + // Constant phys regs are always live. + DstLive = true; + } else { + // For physical registers, see if any register unit containing DstReg + // is live across the DBG_VALUE. + for (MCRegUnitIterator UI(DstReg, TRI); UI.isValid(); ++UI) { + const LiveRange &DstLI = LIS->getRegUnit(*UI); + auto DstLII = DstLI.find(MIIdx); + if (DstLII != DstLI.end() && DstLII->contains(MIIdx)) { + DstLive = true; + break; + } + } + } + + // We now have whether src and dst are live. Best case: we have a DBG_VALUE + // of a live register, coalesing won't change its value. + if ((DstLive && DbgReg == DstReg) || (SrcLive && DbgReg == SrcReg)) + return false; + // If neither register are live, no damage done. + if (!DstLive && !SrcLive) + return false; + // Otherwise, we will end up resurrecting the DBG_VALUE with a different + // register, which is unsafe. + return true; +} + void RegisterCoalescer::updateRegDefsUses(unsigned SrcReg, unsigned DstReg, unsigned SubIdx) { @@ -1830,6 +1890,20 @@ ShrinkMask = LaneBitmask::getNone(); ShrinkMainRange = false; + // Although we can update the DBG_VALUEs to the merged register, as debug uses + // do not contribute to liveness it might not be a sound update. Collect + // DBG_VALUEs that would change value were this interval merging to succeed. + SmallVector DbgValuesToChange; + auto CheckForDbgUser = [this, &CP, &DbgValuesToChange](MachineInstr &MI) { + if (MI.isDebugValue() && MI.getOperand(0).isReg() && + mergingChangesDbgValue(&MI, CP.getSrcReg(), CP.getDstReg())) + DbgValuesToChange.push_back(&MI); + }; + for (auto &RegIt : MRI->reg_instructions(CP.getSrcReg())) + CheckForDbgUser(RegIt); + for (auto &RegIt : MRI->reg_instructions(CP.getDstReg())) + CheckForDbgUser(RegIt); + // Okay, attempt to join these two intervals. On failure, this returns false. // Otherwise, if one of the intervals being joined is a physreg, this method // always canonicalizes DstInt to be it. The output "SrcInt" will not have @@ -1898,6 +1972,16 @@ updateRegDefsUses(CP.getDstReg(), CP.getDstReg(), CP.getDstIdx()); updateRegDefsUses(CP.getSrcReg(), CP.getDstReg(), CP.getSrcIdx()); + // The updates to these DBG_VALUEs are not sound -- mark them undef. + // FIXME: further analysis might recover them, this is the minimal sound + // solution. + for (MachineInstr *MI : DbgValuesToChange) { + assert(MI->getOperand(0).isReg()); + LLVM_DEBUG(dbgs() << "Update of " << MI->getOperand(0) << " would be " + << "unsound, setting undef\n"); + MI->getOperand(0).setReg(0); + } + // Shrink subregister ranges if necessary. if (ShrinkMask.any()) { LiveInterval &LI = LIS->getInterval(CP.getDstReg()); Index: test/CodeGen/X86/pr40010.mir =================================================================== --- /dev/null +++ test/CodeGen/X86/pr40010.mir @@ -0,0 +1,243 @@ +# RUN: llc %s -o - -run-pass=simple-register-coalescing | FileCheck %s +# PR40010: DBG_VALUEs do not contribute to the liveness of virtual registers, +# and the register coalescer would merge new live values on top of DBG_VALUEs, +# leading to them presenting new (wrong) values to the debugger. Test that +# when out of liveness, coalescing will mark DBG_VALUEs in non-live locations +# as undef. +--- | + ; ModuleID = './test.ll' + source_filename = "./test.ll" + target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128" + + ; Function Attrs: nounwind readnone speculatable + declare void @llvm.dbg.value(metadata, metadata, metadata) #0 + + ; Original IR source here: + define i32 @test(i32* %pin) { + entry: + br label %start.test1 + + start.test1: ; preds = %start, %entry + %foo = phi i32 [ 0, %entry ], [ %bar, %start.test1 ] + %baz = load i32, i32* %pin, align 1 + %qux = xor i32 %baz, 1234 + %bar = add i32 %qux, %foo + call void @llvm.dbg.value(metadata i32 %foo, metadata !3, metadata !DIExpression()), !dbg !5 + %cmp = icmp ugt i32 %bar, 1000000 + br i1 %cmp, label %leave, label %start.test1 + + leave: ; preds = %start + ret i32 %bar + } + + ; Stubs to appease the MIR parser + define i32 @test2(i32* %pin) { + entry: + ret i32 0 + start.test2: + ret i32 0 + leave: + ret i32 0 + } + + define i32 @test3(i32* %pin) { + entry: + ret i32 0 + start.test3: + ret i32 0 + leave: + ret i32 0 + } + + define i32 @test4(i32* %pin) { + entry: + ret i32 0 + start.test4: + ret i32 0 + leave: + ret i32 0 + } + + ; Function Attrs: nounwind + declare void @llvm.stackprotector(i8*, i8**) #1 + + attributes #0 = { nounwind readnone speculatable } + attributes #1 = { nounwind } + + !llvm.module.flags = !{!0} + !llvm.dbg.cu = !{!1} + + !0 = !{i32 2, !"Debug Info Version", i32 3} + !1 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !2, producer: "beards", isOptimized: true, runtimeVersion: 4, emissionKind: FullDebug) + !2 = !DIFile(filename: "bees.cpp", directory: "") + !3 = !DILocalVariable(name: "bees", scope: !4) + !4 = distinct !DISubprogram(name: "nope", scope: !1, file: !2, line: 1, spFlags: DISPFlagDefinition, unit: !1) + !5 = !DILocation(line: 0, scope: !4) + +... +--- +name: test +tracksRegLiveness: true +body: | + bb.0.entry: + successors: %bb.1(0x80000000) + liveins: $rdi + + %2:gr64 = COPY killed $rdi + %3:gr32 = MOV32r0 implicit-def dead $eflags + %4:gr32 = MOV32ri 1234 + %7:gr32 = COPY killed %3 + + bb.1.start.test1: + successors: %bb.2(0x04000000), %bb.1(0x7c000000) + + ; CHECK-LABEL: name: test + ; + ; We currently expect %1 and %0 to merge into %7 + ; + ; CHECK: %[[REG1:[0-9]+]]:gr32 = MOV32rm + ; CHECK-NEXT: %[[REG2:[0-9]+]]:gr32 = XOR32rr %[[REG1]] + ; CHECK-NEXT: %[[REG3:[0-9]+]]:gr32 = ADD32rr %[[REG3]], %[[REG2]] + ; CHECK-NEXT: DBG_VALUE $noreg + + %0:gr32 = COPY killed %7 + %8:gr32 = MOV32rm %2, 1, $noreg, 0, $noreg :: (load 4 from %ir.pin, align 1) + %5:gr32 = COPY killed %8 + %5:gr32 = XOR32rr %5, %4, implicit-def dead $eflags + %1:gr32 = COPY killed %0 + %1:gr32 = ADD32rr %1, killed %5, implicit-def dead $eflags + DBG_VALUE %0, $noreg, !3, !DIExpression(), debug-location !5 + CMP32ri %1, 1000001, implicit-def $eflags + %7:gr32 = COPY %1 + JB_1 %bb.1, implicit killed $eflags + JMP_1 %bb.2 + + bb.2.leave: + $eax = COPY killed %1 + RET 0, killed $eax + +... +--- +name: test2 +tracksRegLiveness: true +body: | + bb.0.entry: + successors: %bb.1(0x80000000) + liveins: $rdi + + %2:gr64 = COPY killed $rdi + %3:gr32 = MOV32r0 implicit-def dead $eflags + %4:gr32 = MOV32ri 1234 + %7:gr32 = COPY killed %3 + + bb.1.start.test2: + successors: %bb.2(0x04000000), %bb.1(0x7c000000) + + ; CHECK-LABEL: name: test2 + ; + ; %0 should be merged into %7, but as %0 is live at this location the + ; DBG_VALUE should be preserved and point at the operand of ADD32rr. + ; + ; CHECK: %[[REG11:[0-9]+]]:gr32 = MOV32rm + ; CHECK-NEXT: %[[REG12:[0-9]+]]:gr32 = XOR32rr %[[REG11]] + ; CHECK-NEXT: DBG_VALUE %[[REG13:[0-9]+]] + ; CHECK-NEXT: %[[REG13]]:gr32 = ADD32rr %[[REG13]], %[[REG12]] + + %0:gr32 = COPY killed %7 + %8:gr32 = MOV32rm %2, 1, $noreg, 0, $noreg :: (load 4 from %ir.pin, align 1) + %5:gr32 = COPY killed %8 + %5:gr32 = XOR32rr %5, %4, implicit-def dead $eflags + DBG_VALUE %0, $noreg, !3, !DIExpression(), debug-location !5 + %1:gr32 = COPY killed %0 + %1:gr32 = ADD32rr %1, killed %5, implicit-def dead $eflags + CMP32ri %1, 1000001, implicit-def $eflags + %7:gr32 = COPY %1 + JB_1 %bb.1, implicit killed $eflags + JMP_1 %bb.2 + + bb.2.leave: + $eax = COPY killed %1 + RET 0, killed $eax + +... +--- +name: test3 +tracksRegLiveness: true +body: | + bb.0.entry: + successors: %bb.1(0x80000000) + liveins: $rdi + + %2:gr64 = COPY killed $rdi + %3:gr32 = MOV32r0 implicit-def dead $eflags + %4:gr32 = MOV32ri 1234 + %7:gr32 = COPY killed %3 + + bb.1.start.test3: + successors: %bb.2(0x04000000), %bb.1(0x7c000000) + + ; CHECK-LABEL: name: test3 + ; + ; This is a use-before-def, merging new registers into %0 could unsoundly + ; make it live again, on merge mark it undef. + ; + ; CHECK: DBG_VALUE $noreg + + DBG_VALUE %0, $noreg, !3, !DIExpression(), debug-location !5 + %0:gr32 = COPY killed %7 + %8:gr32 = MOV32rm %2, 1, $noreg, 0, $noreg :: (load 4 from %ir.pin, align 1) + %5:gr32 = COPY killed %8 + %5:gr32 = XOR32rr %5, %4, implicit-def dead $eflags + %1:gr32 = COPY killed %0 + %1:gr32 = ADD32rr %1, killed %5, implicit-def dead $eflags + CMP32ri %1, 1000001, implicit-def $eflags + %7:gr32 = COPY %1 + JB_1 %bb.1, implicit killed $eflags + JMP_1 %bb.2 + + bb.2.leave: + $eax = COPY killed %1 + RET 0, killed $eax + +... +--- +name: test4 +tracksRegLiveness: true +body: | + bb.0.entry: + successors: %bb.1(0x80000000) + liveins: $rdi + + %2:gr64 = COPY killed $rdi + %3:gr32 = MOV32r0 implicit-def dead $eflags + %4:gr32 = MOV32ri 1234 + %7:gr32 = COPY killed %3 + + bb.1.start.test4: + successors: %bb.2(0x04000000), %bb.1(0x7c000000) + + ; CHECK-LABEL: name: test4 + ; + ; Using a dead register, even if we coalesce it to the right value, should + ; be marked undef. The coalescer can't prove it's correct without + ; considering control flow in the general case. + ; + ; CHECK: DBG_VALUE $noreg + + %0:gr32 = COPY killed %7 + DBG_VALUE %7, $noreg, !3, !DIExpression(), debug-location !5 + %8:gr32 = MOV32rm %2, 1, $noreg, 0, $noreg :: (load 4 from %ir.pin, align 1) + %5:gr32 = COPY killed %8 + %5:gr32 = XOR32rr %5, %4, implicit-def dead $eflags + %1:gr32 = COPY killed %0 + %1:gr32 = ADD32rr %1, killed %5, implicit-def dead $eflags + CMP32ri %1, 1000001, implicit-def $eflags + %7:gr32 = COPY %1 + JB_1 %bb.1, implicit killed $eflags + JMP_1 %bb.2 + + bb.2.leave: + $eax = COPY killed %1 + RET 0, killed $eax + +...