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Prevent FENTRY_CALL reordering

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FEntryInserter prepends FENTRY_CALL to the first basic block. In case
there are other instructions, PostRA Machine Instruction Scheduler can
move FENTRY_CALL call around. This actually occurs on SystemZ (see the
testcase). This is bad for the following reasons:

* FENTRY_CALL clobbers registers.
* Linux Kernel depends on whatever FENTRY_CALL expands to to be the very
  first instruction in the function.

Fix by adding isCall attribute to FENTRY_CALL, which prevents reordering
by making it a scheduling boundary for PostRA Machine Instruction
Scheduler.

Reviewed By: niravd

Differential Revision: https://reviews.llvm.org/D91218
This commit is contained in:
Ilya Leoshkevich 2020-12-08 22:04:00 +01:00
parent 88c99ea84d
commit 942af666c6
4 changed files with 43 additions and 0 deletions
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1
include/llvm/Target/Target.td
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@ -1282,6 +1282,7 @@ def FENTRY_CALL : StandardPseudoInstruction {
let InOperandList = (ins);
let AsmString = "# FEntry call";
let usesCustomInserter = true;
let isCall = true;
let mayLoad = true;
let mayStore = true;
let hasSideEffects = true;

1
lib/CodeGen/MachineInstr.cpp
View File

@ -713,6 +713,7 @@ bool MachineInstr::isCandidateForCallSiteEntry(QueryType Type) const {
case TargetOpcode::PATCHPOINT:
case TargetOpcode::STACKMAP:
case TargetOpcode::STATEPOINT:
case TargetOpcode::FENTRY_CALL:
return false;
}
return true;

22
test/CodeGen/SystemZ/fentry-debug-info.ll Normal file
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@ -0,0 +1,22 @@
; Test that compiling with fentry and debuginfo works.
;
; RUN: llc %s -mtriple=s390x-linux-gnu -o - -verify-machineinstrs
define dso_local void @_Z1av() local_unnamed_addr #0 !dbg !7 {
entry:
ret void
}
attributes #0 = { norecurse nounwind readnone "fentry-call"="true" }
!llvm.dbg.cu = !{!0}
!llvm.module.flags = !{!3, !4}
!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !1, producer: "clang version 12.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, splitDebugInlining: false, nameTableKind: None)
!1 = !DIFile(filename: "a.cpp", directory: "/tmp")
!2 = !{}
!3 = !{i32 7, !"Dwarf Version", i32 4}
!4 = !{i32 2, !"Debug Info Version", i32 3}
!7 = distinct !DISubprogram(name: "a", linkageName: "_Z1av", scope: !1, file: !1, line: 1, type: !8, scopeLine: 1, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2)
!8 = !DISubroutineType(types: !9)
!9 = !{null}

19
test/CodeGen/SystemZ/fentry-no-reorder.ll Normal file
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@ -0,0 +1,19 @@
; RUN: llc %s -mtriple=s390x-linux-gnu -mcpu=zEC12 -o - -verify-machineinstrs \
; RUN: | FileCheck %s
@PawnTT = dso_local local_unnamed_addr global [2048 x i8] zeroinitializer, align 2
define dso_local void @clear_pawn_tt() local_unnamed_addr #0 {
entry:
call void @llvm.memset.p0i8.i64(i8* nonnull align 2 dereferenceable(2048) getelementptr inbounds ([2048 x i8], [2048 x i8]* @PawnTT, i64 0, i64 0), i8 0, i64 2048, i1 false)
ret void
}
declare void @llvm.memset.p0i8.i64(i8* nocapture writeonly, i8, i64, i1 immarg) #1
attributes #0 = { nofree nounwind writeonly "fentry-call"="true" }
attributes #1 = { argmemonly nofree nosync nounwind willreturn writeonly }
; CHECK: clear_pawn_tt: # @clear_pawn_tt
; CHECK-NEXT: # %bb.0:
; CHECK-NEXT: brasl %r0, __fentry__@PLT