[all-commits] [llvm/llvm-project] 5ad59c: [RISCV][NFCI] Set TransientStackAlignment and rely...
Alex Bradbury via All-commits
all-commits at lists.llvm.org
Tue Aug 2 01:46:40 PDT 2022
Author: Alex Bradbury <asb at igalia.com>
Date: 2022-08-02 (Tue, 02 Aug 2022)
[RISCV][NFCI] Set TransientStackAlignment and rely on it rather than RVV-specific logic on RVV-less functions
* TargetFrameLowering has a TransientStackAlignment field that "returns
the number of bytes to which the stack pointer must be aligned at all
times, even between calls.
* As explained in the [RISC-V calling
the stack pointer must remain fully aligned throughout execution for
compliant code. This is important for embedded targets that might avoid
realigning the stack pointer for interrupt service routines. Systems
running full OSes may always realign the stack anyway.
* TransientStackAlignment is used in estimateStackSize in
MachineFrameInfo and in PEI::calculateFrameObjectOffsets.
* estimateStackSize is only used in the RISC-V backend for scavenging
slots. It may be possible to craft a function where the difference
is observable, but it wouldn't be a meaningful test.
* calculateFrameObjectOffsets makes use of TransientStackAlignment,
but then sets the stack alignment to the max of that alignment and
MaxAlign, which is unconditionally set to 16 in
* I've changed this logic to only set MaxAlign if there are RVV frame
objects. There should be no functional change here for either RVV
targets (MaxAlign is set as before) or non-RVV targets
(TransientStackAlign is now 16 anyway).
Differential Revision: https://reviews.llvm.org/D130068
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