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b7a99b0894
This patch changes the location of the frame-record (FP, LR) to the
bottom of the callee-saved area. According to the AAPCS the location of
the frame-record within the stackframe is unspecified (section 5.2.3 The
Frame Pointer), so the compiler should be free to choose a different
location.
The reason for changing the location of the frame-record is to prepare
the frame for allocating an SVE area below the callee-saves. This way the
compiler can use the VL-scaled addressing modes to directly access SVE
objects from the frame-pointer.
: :
| stack | | stack |
| args | | args |
+-------+ +-------+
| x30 | | x19 |
| x29 | | x20 |
FP -> |- - - -| | x21 |
| x19 | ==> | x22 |
| x20 | |- - - -|
| x21 | | x30 |
| x22 | | x29 |
+-------+ +-------+ <- FP
|///////| |///////| // realignment gap
|- - - -| |- - - -|
|spills/| |spills/|
| locals| | locals|
SP -> +-------+ +-------+ <- SP
Things to point out:
- The algorithm to find a paired register should be prevented from
accidentally pairing some callee-saved register with LR that is not
FP, since they should always be paired together when the frame
has a frame-record.
- For Darwin platforms the location of the frame-record is unchanged,
since the unwind encoding does not allow for encoding this position
dynamically and other tools currently depend on the former layout.
Reviewers: efriedma, rovka, rengolin, thegameg, greened, t.p.northover
Reviewed By: efriedma
Differential Revision: https://reviews.llvm.org/D65653
llvm-svn: 368987
36 lines
1.3 KiB
YAML
36 lines
1.3 KiB
YAML
# RUN: llc -mtriple=aarch64-none-linux-gnu -run-pass=prologepilog %s -o - | FileCheck %s
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# Ensure references to scavenged stack slots in the CSR area use the
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# FP as a base when the stack pointer must be aligned to something
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# larger than required by the target. This is necessary because the
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# alignment padding area is between the CSR area and the SP, so the SP
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# cannot be used to reference the CSR area.
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name: test
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tracksRegLiveness: true
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frameInfo:
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maxAlignment: 64
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# CHECK: stack:
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# CHECK: id: 0, name: '', type: default, offset: -64, size: 4, alignment: 64
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# CHECK-NEXT: stack-id: default
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# CHECK-NEXT: local-offset: -64
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# CHECK: id: 1, name: '', type: default, offset: -4, size: 4, alignment: 4
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# CHECK-NEXT: stack-id: default
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# CHECK-NEXT: local-offset: -68
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stack:
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- { id: 0, size: 4, alignment: 64, local-offset: -64 }
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- { id: 1, size: 4, alignment: 4, local-offset: -68 }
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# CHECK: body:
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# CHECK: $sp = ANDXri killed ${{x[0-9]+}}, 7865
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# CHECK: STRSui $s0, $sp, 0
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# CHECK: STRSui $s0, $fp, 7
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body: |
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bb.0.entry:
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liveins: $s0
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STRSui $s0, %stack.0, 0
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STRSui $s0, %stack.1, 0
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; Force preserve a CSR to create a hole in the CSR stack region.
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$x28 = IMPLICIT_DEF
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RET_ReallyLR
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