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[BOLT] Handle insertion of updated CFI at the first basic block 

Summary:
Fix corner case of insertion of updated CFI with unset `PrevBB`.
Handle it in the same way as inserting past hot-cold split point.

(cherry picked from FBD24943911)
This commit is contained in:
Amir Ayupov 2020-11-17 18:40:19 -08:00 committed by Maksim Panchenko
parent 1cf23e5ee8
commit f9d00d418b
2 changed files with 43 additions and 2 deletions
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4
bolt/src/Passes/ShrinkWrapping.cpp
View File

@ -1576,8 +1576,8 @@ void ShrinkWrapping::insertUpdatedCFI(unsigned CSR, int SPValPush,
}
}
}
// Are we at the hot-cold split point?
if (BF.isSplit() && PrevBB && BB->isCold() != PrevBB->isCold()) {
// Are we at the first basic block or hot-cold split point?
if (!PrevBB || (BF.isSplit() && BB->isCold() != PrevBB->isCold())) {
if (InAffectedZoneAtBegin) {
insertCFIsForPushOrPop(*BB, BB->begin(), CSR, true, 0, SPValPush);
}

41
bolt/test/X86/shrinkwrapping-insertcfi.s Normal file
View File

@ -0,0 +1,41 @@
# This test reproduces the issue with inserting updated CFI in shrink wrapping
# into the first basic block.
# REQUIRES: system-linux
# RUN: llvm-mc -filetype=obj -triple x86_64-unknown-unknown %s -o %t.o
# RUN: link_fdata %s %t.o %t.fdata
# RUN: strip --strip-unneeded %t.o
# RUN: %host_cc %t.o -o %t.exe -Wl,-q -nostdlib
# RUN: llvm-bolt %t.exe -o %t.out -data %t.fdata -frame-opt=all -lite=0 \
# RUN: -print-fop 2>&1 | FileCheck %s
# Check shrink wrapping results:
# CHECK: BOLT-INFO: Shrink wrapping moved 0 spills inserting load/stores and 1 spills inserting push/pops
# Check that CFI is successfully inserted into the first basic block:
# CHECK: Binary Function "_start" after frame-optimizer
# CHECK: .LBB0 (2 instructions, align : 1)
# CHECK-NEXT: Entry Point
# CHECK: 00000000: !CFI {{.*}}
# CHECK-NEXT: 00000000: je .Ltmp{{.*}}
.globl _start
_start:
.cfi_startproc
# FDATA: 0 [unknown] 0 1 _start 0 0 6
# !CFI OpOffset for reg3/rbx is inserted into this block.
je a
b: jne _start
# FDATA: 1 _start #b# 1 _start #c# 0 3
c:
push %rbx
.cfi_offset 3, 4
pop %rbx
# This basic block is treated as having 0 execution count.
# push and pop will be sinked into this block.
a:
ud2
.cfi_endproc