[all-commits] [llvm/llvm-project] 643b64: [RISCV] Avoid scalar outgoing argumetns overwritin...

[Kai Wang via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 643b6407faf460915679f304420cfbee87c47734
      https://github.com/llvm/llvm-project/commit/643b6407faf460915679f304420cfbee87c47734
  Author: Hsiangkai Wang <kai.wang at sifive.com>
  Date:   2021-06-11 (Fri, 11 Jun 2021)

  Changed paths:
    M llvm/lib/Target/RISCV/RISCVFrameLowering.cpp
    M llvm/test/CodeGen/RISCV/rvv/rvv-out-arguments.ll

  Log Message:
  -----------
  [RISCV] Avoid scalar outgoing argumetns overwriting vector frame objects.

When using FP to access stack objects, the scalable stack objects will
be put at the lower end of the frame. It looks like

```
|-------------------|  <-- FP
| callee-saved regs |
|-------------------|
| scalar local vars |
|-------------------|
| RVV local vars    |
|-------------------|  <-- SP
```

If there are scalar arguments that need to pass through memory and there
are vector objects on the stack using FP to access. The outgoing scalar
arguments will overwrite the vector objects. It looks like

```
|-------------------|  <-- FP
| callee-saved regs |
|-------------------|
| scalar local vars |
|-------------------|         |-------------------|
| RVV local vars    |         | outgoing args     | <- outgoing arguments
|-------------------|  <-- SP |-------------------|    overwrite from here.
```

In this patch, we reserve the stack for the outgoing arguments before
function calls if using FP to access and there are scalable vector frame
objects. It looks like

```
|-------------------|  <-- FP
| callee-saved regs |
|-------------------|
| scalar local vars |
|-------------------|
| RVV local vars    |
|-------------------|
| outgoing args     |
|-------------------|  <-- SP
```

Differential Revision: https://reviews.llvm.org/D103622