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[CodeGen] Fix unconditional branch duplication issue in bbsections

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If an end section basic block ends in an unconditional branch to its
fallthrough, BasicBlockSections will duplicate the unconditional branch.
This doesn't break x86, but it is a (slight) size optimization and more
importantly prevents AArch64 builds from breaking.

Ex:
```
bb1 (bbsections Hot):
  jmp bb2

bb2 (bbsections Cold):
  /* do work... */
```

After running sortBasicBlocksAndUpdateBranches():
```
bb1 (bbsections Hot):
  jmp bb2
  jmp bb2

bb2 (bbsections Cold):
  /* do work... */
```

Differential Revision: https://reviews.llvm.org/D158674
This commit is contained in:
Daniel Hoekwater 2023-08-21 16:29:02 +00:00
parent 4ad89131e0
commit 994eb5adc4
2 changed files with 27 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
llvm/lib/CodeGen/BasicBlockSections.cpp
View File

@ -258,7 +258,8 @@ void llvm::sortBasicBlocksAndUpdateBranches(
[[maybe_unused]] const MachineBasicBlock *EntryBlock = &MF.front();
SmallVector<MachineBasicBlock *> PreLayoutFallThroughs(MF.getNumBlockIDs());
for (auto &MBB : MF)
PreLayoutFallThroughs[MBB.getNumber()] = MBB.getFallThrough();
PreLayoutFallThroughs[MBB.getNumber()] =
MBB.getFallThrough(/*JumpToFallThrough=*/false);
MF.sort(MBBCmp);
assert(&MF.front() == EntryBlock &&

25
llvm/test/CodeGen/Generic/machine-function-splitter.ll
View File

@ -6,11 +6,13 @@
; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu -split-machine-functions -mfs-psi-cutoff=0 -mfs-count-threshold=2000 | FileCheck %s --dump-input=always -check-prefixes=MFS-OPTS1,MFS-OPTS1-X86
; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu -split-machine-functions -mfs-psi-cutoff=950000 | FileCheck %s -check-prefixes=MFS-OPTS2,MFS-OPTS2-X86
; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu -split-machine-functions -mfs-split-ehcode | FileCheck %s -check-prefixes=MFS-EH-SPLIT,MFS-EH-SPLIT-X86
; RUN: llc < %s -mtriple=x86_64 -split-machine-functions -O0 -mfs-psi-cutoff=0 -mfs-count-threshold=10000 | FileCheck %s -check-prefixes=MFS-O0,MFS-O0-X86
; RUN: llc < %s -mtriple=aarch64-unknown-linux-gnu -enable-split-machine-functions -mfs-allow-unsupported-triple | FileCheck %s -check-prefixes=MFS-DEFAULTS,MFS-DEFAULTS-AARCH64
; RUN: llc < %s -mtriple=aarch64-unknown-linux-gnu -enable-split-machine-functions -mfs-allow-unsupported-triple -mfs-psi-cutoff=0 -mfs-count-threshold=2000 | FileCheck %s --dump-input=always -check-prefixes=MFS-OPTS1,MFS-OPTS1-AARCH64
; RUN: llc < %s -mtriple=aarch64-unknown-linux-gnu -enable-split-machine-functions -mfs-allow-unsupported-triple -mfs-psi-cutoff=950000 | FileCheck %s -check-prefixes=MFS-OPTS2,MFS-OPTS2-AARCH64
; RUN: llc < %s -mtriple=aarch64-unknown-linux-gnu -enable-split-machine-functions -mfs-allow-unsupported-triple -mfs-split-ehcode | FileCheck %s -check-prefixes=MFS-EH-SPLIT,MFS-EH-SPLIT-AARCH64
; RUN: llc < %s -mtriple=aarch64 -enable-split-machine-functions -O0 -mfs-allow-unsupported-triple -mfs-psi-cutoff=0 -mfs-count-threshold=10000 | FileCheck %s --dump-input=always -check-prefixes=MFS-O0,MFS-O0-AARCH64
; COM: Machine function splitting with AFDO profiles
; RUN: sed 's/InstrProf/SampleProfile/g' %s > %t.ll
@ -462,6 +464,29 @@ define void @foo15(i1 zeroext %0, i1 zeroext %1) nounwind !prof !27 {
ret void
}
define void @foo16(i1 zeroext %0) nounwind !prof !14 !section_prefix !15 {
;; Check that an unconditional branch is only appended to a block
;; if it would fall through to the wrong block otherwise.
; MFS-O0-LABEL: foo16
; MFS-O0-X86: jmp
; MFS-O0-X86-NOT: jmp
; MFS-O0-AARCH64: br
; MFS-O0-AARCH64: br
; MFS-O0-AARCH64-NOT: br
; MFS-O0: .section .text.split.foo16
; MFS-O0-NEXT: foo16.cold
%2 = call i32 @baz()
br i1 false, label %3, label %5, !prof !25
3: ; preds = %1
%4 = call i32 @bar()
unreachable
5: ; preds = %1
%6 = tail call i32 @qux()
ret void
}
declare i32 @bar()
declare i32 @baz()
declare i32 @bam()