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[BOLT][AArch64] Reduce the number of ADR relaxations #111577

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Merged
merged 3 commits into from
Oct 8, 2024
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[BOLT][AArch64] Reduce the number of ADR relaxations #111577

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[BOLT][AArch64] Reduce the number of ADR relaxations
maksfb Sep 14, 2024
f317403
fixup! [BOLT][AArch64] Reduce the number of ADR relaxations
maksfb Oct 8, 2024
759f0d6
fixup! fixup! [BOLT][AArch64] Reduce the number of ADR relaxations
maksfb Oct 8, 2024
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7 changes: 4 additions & 3 deletions bolt/lib/Passes/ADRRelaxationPass.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -56,13 +56,14 @@ void ADRRelaxationPass::runOnFunction(BinaryFunction &BF) {
continue;
}

// Don't relax adr if it points to the same function and it is not split
// and BF initial size is < 1MB.
// Don't relax ADR if it points to the same function and is in the main
// fragment and BF initial size is < 1MB.
const unsigned OneMB = 0x100000;
if (BF.getSize() < OneMB) {
BinaryFunction *TargetBF = BC.getFunctionForSymbol(Symbol);
if (TargetBF == &BF && !BF.isSplit())
if (TargetBF == &BF && !BB.isSplit())
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@dcci dcci Oct 8, 2024

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This looks fine to me. Can we add a negative test? (e.g. one where the func is not in the main fragment to show the adrp is still there?)

continue;

// No relaxation needed if ADR references a basic block in the same
// fragment.
if (BinaryBasicBlock *TargetBB = BF.getBasicBlockForLabel(Symbol))
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49 changes: 49 additions & 0 deletions bolt/test/AArch64/adr-relaxation.s
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@@ -0,0 +1,49 @@
## Check that llvm-bolt will not unnecessarily relax ADR instruction.

# RUN: llvm-mc -filetype=obj -triple aarch64-unknown-unknown %s -o %t.o
# RUN: %clang %cflags %t.o -o %t.exe -Wl,-q -static
# RUN: llvm-bolt %t.exe -o %t.bolt --split-functions --split-strategy=random2
# RUN: llvm-objdump -d --disassemble-symbols=_start %t.bolt | FileCheck %s
# RUN: llvm-objdump -d --disassemble-symbols=foo.cold.0 %t.bolt \
# RUN: | FileCheck --check-prefix=CHECK-FOO %s

## ADR below references its containing function that is split. But ADR is always
## in the main fragment, thus there is no need to relax it.
.text
.globl _start
.type _start, %function
_start:
# CHECK: <_start>:
.cfi_startproc
adr x1, _start
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@yota9 yota9 Oct 8, 2024

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Indentation

# CHECK-NOT: adrp
# CHECK: adr
cmp x1, x11
b.hi .L1
mov x0, #0x0
.L1:
ret x30
.cfi_endproc
.size _start, .-_start


## In foo, ADR is in the split fragment but references the main one. Thus, it
## needs to be relaxed into ADRP + ADD.
.globl foo
.type foo, %function
foo:
.cfi_startproc
cmp x1, x11
b.hi .L2
mov x0, #0x0
.L2:
# CHECK-FOO: <foo.cold.0>:
adr x1, foo
# CHECK-FOO: adrp
# CHECK-FOO-NEXT: add
ret x30
.cfi_endproc
.size foo, .-foo

## Force relocation mode.
.reloc 0, R_AARCH64_NONE
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