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[AArch64][v8.5A] Don't create BR instructions in outliner when BTI enabled
When branch target identification is enabled, we can only do indirect tail-calls through x16 or x17. This means that the outliner can't transform a BLR instruction at the end of an outlined region into a BR. Differential revision: https://reviews.llvm.org/D52869 llvm-svn: 343969
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@ -5084,6 +5084,13 @@ AArch64InstrInfo::getOutliningCandidateInfo(
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unsigned FrameID = MachineOutlinerDefault;
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unsigned NumBytesToCreateFrame = 4;
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bool HasBTI =
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std::any_of(RepeatedSequenceLocs.begin(), RepeatedSequenceLocs.end(),
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[](outliner::Candidate &C) {
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return C.getMF()->getFunction().hasFnAttribute(
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"branch-target-enforcement");
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});
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// If the last instruction in any candidate is a terminator, then we should
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// tail call all of the candidates.
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if (RepeatedSequenceLocs[0].back()->isTerminator()) {
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@ -5092,7 +5099,8 @@ AArch64InstrInfo::getOutliningCandidateInfo(
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SetCandidateCallInfo(MachineOutlinerTailCall, 4);
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}
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else if (LastInstrOpcode == AArch64::BL || LastInstrOpcode == AArch64::BLR) {
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else if (LastInstrOpcode == AArch64::BL ||
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(LastInstrOpcode == AArch64::BLR && !HasBTI)) {
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// FIXME: Do we need to check if the code after this uses the value of LR?
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FrameID = MachineOutlinerThunk;
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NumBytesToCreateFrame = 0;
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44
test/CodeGen/AArch64/machine-outliner-bti.mir
Normal file
44
test/CodeGen/AArch64/machine-outliner-bti.mir
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@ -0,0 +1,44 @@
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# RUN: llc -mtriple=aarch64--- -run-pass=prologepilog -run-pass=machine-outliner -verify-machineinstrs %s -o - | FileCheck %s
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# AArch64 Branch Target Enforcement treats the BR and BLR indirect branch
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# instructions differently. The BLR instruction can only target a BTI C
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# instruction, and the BR instruction can only target a BTI J instruction. We
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# always start indirectly-called functions with BTI C, so the outliner must not
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# transform a BLR instruction into a BR instruction.
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# There is an exception to this: BR X16 and BR X17 can also target a BTI C
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# instruction. We make of this for general tail-calls (tested elsewhere), but
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# don't currently make use of this in the outliner.
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# CHECK-NOT: OUTLINED_FUNCTION_
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--- |
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@g = hidden local_unnamed_addr global i32 0, align 4
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define hidden void @bar(void ()* nocapture %f) "branch-target-enforcement" {
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entry:
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ret void
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}
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declare void @foo()
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...
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---
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name: bar
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tracksRegLiveness: true
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body: |
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bb.0.entry:
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liveins: $x20, $x21, $lr, $x19
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HINT 34
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STRWui renamable $w21, renamable $x20, target-flags(aarch64-pageoff, aarch64-nc) @g :: (store 4 into @g)
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BLR renamable $x19, csr_aarch64_aapcs, implicit-def dead $lr, implicit $sp, implicit-def $sp
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STRWui renamable $w21, renamable $x20, target-flags(aarch64-pageoff, aarch64-nc) @g :: (store 4 into @g)
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BLR renamable $x19, csr_aarch64_aapcs, implicit-def dead $lr, implicit $sp, implicit-def $sp
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STRWui killed renamable $w21, killed renamable $x20, target-flags(aarch64-pageoff, aarch64-nc) @g :: (store 4 into @g)
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BLR killed renamable $x19, csr_aarch64_aapcs, implicit-def dead $lr, implicit $sp, implicit-def $sp
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TCRETURNdi @foo, 0, csr_aarch64_aapcs, implicit $sp
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...
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