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[MachineOutliner] Don't outline ADRP pair to avoid incorrect ICF (llvm#160232)
On AArch64, ADRP and its user instructions (LDR, ADD, etc.), that are referencing a GOT symbol, when separated into different functions by machine outliner exposes a correctness issue in the linker ICF. In such cases, user instructions can end up pointing to a folded section (with its canonical folded symbol), while ADRP instruction point to a GOT entry corresponding to the original symbol. This leads to loading from incorrect memory address after ICF. llvm#129122 explains how this can happen in detail. This addresses llvm#131660 which should fix two things: 1. Hide the correctness issue described above in the LLVM linker. 2. Allows optimizations that could relax GOT addressing to PC-relative addressing.
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‎llvm/lib/Target/AArch64/AArch64InstrInfo.cpp‎

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@@ -9590,6 +9590,27 @@ AArch64InstrInfo::getOutliningCandidateInfo(
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unsigned NumBytesToCreateFrame = 0;
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// Avoid splitting ADRP ADD/LDR pair into outlined functions.
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// These instructions are fused together by the scheduler.
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// Any candidate where ADRP is the last instruction should be rejected
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// as that will lead to splitting ADRP pair.
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MachineInstr &LastMI = RepeatedSequenceLocs[0].back();
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MachineInstr &FirstMI = RepeatedSequenceLocs[0].front();
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if (LastMI.getOpcode() == AArch64::ADRP &&
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(LastMI.getOperand(1).getTargetFlags() & AArch64II::MO_PAGE) != 0 &&
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(LastMI.getOperand(1).getTargetFlags() & AArch64II::MO_GOT) != 0) {
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return std::nullopt;
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}
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// Similarly any candidate where the first instruction is ADD/LDR with a
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// page offset should be rejected to avoid ADRP splitting.
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if ((FirstMI.getOpcode() == AArch64::ADDXri ||
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FirstMI.getOpcode() == AArch64::LDRXui) &&
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(FirstMI.getOperand(2).getTargetFlags() & AArch64II::MO_PAGEOFF) != 0 &&
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(FirstMI.getOperand(2).getTargetFlags() & AArch64II::MO_GOT) != 0) {
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return std::nullopt;
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}
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// We only allow outlining for functions having exactly matching return
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// address signing attributes, i.e., all share the same value for the
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// attribute "sign-return-address" and all share the same type of key they

‎llvm/test/CodeGen/AArch64/machine-outliner-adrp-got-split.mir‎

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# RUN: llc -mtriple=aarch64--- -run-pass=machine-outliner -verify-machineinstrs %s -o - | FileCheck %s
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--- |
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@x = common global i32 0, align 4
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define i32 @adrp_add() #0 {
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ret i32 0
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}
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define i32 @adrp_ldr() #0 {
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ret i32 0
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}
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attributes #0 = { noinline noredzone }
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...
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---
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# Check that main function body doesn't split ADRP pair
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#
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# CHECK-LABEL: name: adrp_add
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# CHECK-DAG: bb.0:
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# CHECK: BL @OUTLINED_FUNCTION_[[F0:[0-9]+]]
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# CHECK-NEXT: BL @OUTLINED_FUNCTION_[[F2:[0-9]+]]
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# CHECK-NEXT: $lr = ORRXri $xzr, 1
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name: adrp_add
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tracksRegLiveness: true
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body: |
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bb.0:
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liveins: $lr
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$w12 = ORRWri $wzr, 1
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$w12 = ORRWri $wzr, 1
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$w12 = ORRWri $wzr, 1
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$w12 = ORRWri $wzr, 1
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$w12 = ORRWri $wzr, 1
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$w12 = ORRWri $wzr, 1
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$x9 = ADRP target-flags(aarch64-page, aarch64-got) @x
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$x12 = ADDXri $x9, target-flags(aarch64-pageoff, aarch64-got) @x, 0
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$lr = ORRXri $xzr, 1
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bb.1:
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liveins: $lr
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$w12 = ORRWri $wzr, 1
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$w12 = ORRWri $wzr, 1
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$w12 = ORRWri $wzr, 1
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$w12 = ORRWri $wzr, 1
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$w12 = ORRWri $wzr, 1
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$w12 = ORRWri $wzr, 1
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$x9 = ADRP target-flags(aarch64-page, aarch64-got) @x
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$x12 = ADDXri $x9, target-flags(aarch64-pageoff, aarch64-got) @x, 0
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$lr = ORRXri $xzr, 1
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bb.2:
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liveins: $lr
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$w12 = ORRWri $wzr, 1
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$w12 = ORRWri $wzr, 1
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$w12 = ORRWri $wzr, 1
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$w12 = ORRWri $wzr, 1
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$w12 = ORRWri $wzr, 1
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$w12 = ORRWri $wzr, 1
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$x9 = ADRP target-flags(aarch64-page, aarch64-got) @x
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$x12 = ADDXri $x9, target-flags(aarch64-pageoff, aarch64-got) @x, 0
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$lr = ORRXri $xzr, 1
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bb.3:
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liveins: $lr
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RET undef $lr
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...
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---
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# Check that main function body doesn't split ADRP pair
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#
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# CHECK-LABEL: name: adrp_ldr
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# CHECK-DAG: bb.0:
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# CHECK: BL @OUTLINED_FUNCTION_[[F0]]
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# CHECK-NEXT: BL @OUTLINED_FUNCTION_[[F1:[0-9]+]]
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# CHECK-NEXT: $lr = ORRXri $xzr, 1
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name: adrp_ldr
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tracksRegLiveness: true
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body: |
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bb.0:
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liveins: $lr
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$w12 = ORRWri $wzr, 1
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$w12 = ORRWri $wzr, 1
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$w12 = ORRWri $wzr, 1
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$w12 = ORRWri $wzr, 1
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$w12 = ORRWri $wzr, 1
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$w12 = ORRWri $wzr, 1
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$x9 = ADRP target-flags(aarch64-page, aarch64-got) @x
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$x12 = LDRXui $x9, target-flags(aarch64-pageoff, aarch64-got) @x
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$lr = ORRXri $xzr, 1
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bb.1:
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liveins: $lr
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$w12 = ORRWri $wzr, 1
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$w12 = ORRWri $wzr, 1
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$w12 = ORRWri $wzr, 1
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$w12 = ORRWri $wzr, 1
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$w12 = ORRWri $wzr, 1
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$w12 = ORRWri $wzr, 1
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$x9 = ADRP target-flags(aarch64-page, aarch64-got) @x
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$x12 = LDRXui $x9, target-flags(aarch64-pageoff, aarch64-got) @x
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$lr = ORRXri $xzr, 1
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bb.2:
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liveins: $lr
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$w12 = ORRWri $wzr, 1
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$w12 = ORRWri $wzr, 1
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$w12 = ORRWri $wzr, 1
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$w12 = ORRWri $wzr, 1
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$w12 = ORRWri $wzr, 1
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$w12 = ORRWri $wzr, 1
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$x9 = ADRP target-flags(aarch64-page, aarch64-got) @x
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$x12 = LDRXui $x9, target-flags(aarch64-pageoff, aarch64-got) @x
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$lr = ORRXri $xzr, 1
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bb.3:
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liveins: $lr
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RET undef $lr
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# Check that no outlined function split the ADRP pair apart
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#
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# CHECK: OUTLINED_FUNCTION_[[F0]]
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# CHECK-DAG: bb.0
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# CHECK: $w12 = ORRWri $wzr, 1
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# CHECK-NEXT: $w12 = ORRWri $wzr, 1
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# CHECK-NEXT: $w12 = ORRWri $wzr, 1
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# CHECK-NEXT: $w12 = ORRWri $wzr, 1
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# CHECK-NEXT: $w12 = ORRWri $wzr, 1
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# CHECK-NEXT: RET $lr
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# CHECK: OUTLINED_FUNCTION_[[F1]]
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# CHECK-DAG: bb.0
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# CHECK: $w12 = ORRWri $wzr, 1
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# CHECK-NEXT: $x9 = ADRP target-flags(aarch64-page, aarch64-got) @x
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# CHECK-NEXT: $x12 = LDRXui $x9, target-flags(aarch64-pageoff, aarch64-got) @x
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# CHECK: name: OUTLINED_FUNCTION_[[F2]]
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# CHECK-DAG: bb.0
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# CHECK: $w12 = ORRWri $wzr, 1
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# CHECK-NEXT: $x9 = ADRP target-flags(aarch64-page, aarch64-got) @x
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# CHECK-NEXT: $x12 = ADDXri $x9, target-flags(aarch64-pageoff, aarch64-got) @x, 0

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