50a97aacac
Re-commit of 32e8b550e5
This patch rearranges emission of CFI instructions, so the resulting
DWARF and `.eh_frame` information is precise at every instruction.
The current state is that the unwind info is emitted only after the
function prologue. This is fine for synchronous (e.g. C++) exceptions,
but the information is generally incorrect when the program counter is
at an instruction in the prologue or the epilogue, for example:
```
stp x29, x30, [sp, #-16]! // 16-byte Folded Spill
mov x29, sp
.cfi_def_cfa w29, 16
...
```
after the `stp` is executed the (initial) rule for the CFA still says
the CFA is in the `sp`, even though it's already offset by 16 bytes
A correct unwind info could look like:
```
stp x29, x30, [sp, #-16]! // 16-byte Folded Spill
.cfi_def_cfa_offset 16
mov x29, sp
.cfi_def_cfa w29, 16
...
```
Having this information precise up to an instruction is useful for
sampling profilers that would like to get a stack backtrace. The end
goal (towards this patch is just a step) is to have fully working
`-fasynchronous-unwind-tables`.
Reviewed By: danielkiss, MaskRay
Differential Revision: https://reviews.llvm.org/D111411
44 lines
1.3 KiB
LLVM
44 lines
1.3 KiB
LLVM
; RUN: llc -verify-machineinstrs < %s | FileCheck %s
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; The purpose of this test is to construct a scenario where an odd number
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; of callee-saved GPRs as well as an odd number of callee-saved FPRs are
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; used. This caused the frame pointer to be aligned to a multiple of 8
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; on non-Darwin platforms, rather than a multiple of 16 as usual.
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target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
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target triple = "aarch64-unknown-linux-gnu"
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@a = global i64 0, align 4
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define i64 @b() {
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entry:
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%call = tail call i64 @d()
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%0 = alloca i8, i64 ptrtoint (i64 ()* @d to i64), align 16
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%1 = ptrtoint i8* %0 to i64
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store i64 %1, i64* @a, align 4
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%call1 = call i64 @e()
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%conv = sitofp i64 %call1 to float
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%2 = load i64, i64* @a, align 4
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%call2 = call i64 @f(i64 %2)
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%conv3 = fptosi float %conv to i64
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ret i64 %conv3
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}
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; CHECK-LABEL: b:
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; CHECK: str d8, [sp, #-32]!
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; CHECK-NEXT: .cfi_def_cfa_offset 32
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; CHECK-NEXT: stp x29, x30, [sp, #8]
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; CHECK-NEXT: str x19, [sp, #24]
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; CHECK-NEXT: add x29, sp, #8
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; CHECK: sub sp, x29, #8
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; CHECK-NEXT: ldp x29, x30, [sp, #8]
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; CHECK-NEXT: ldr x19, [sp, #24]
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; CHECK-NEXT: ldr d8, [sp], #32
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; CHECK-NEXT: ret
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declare i64 @d()
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declare i64 @e()
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declare i64 @f(i64)
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