[RISCV] Add support for _interrupt attribute

- Save/restore only registers that are used.
This includes Callee saved registers and Caller saved registers
(arguments and temporaries) for integer and FP registers.
- If there is a call in the interrupt handler, save/restore all
Caller saved registers (arguments and temporaries) and all FP registers.
- Emit special return instructions depending on "interrupt"
attribute type.
Based on initial patch by Zhaoshi Zheng.

Reviewers: asb

Reviewed By: asb

Subscribers: rkruppe, the_o, MartinMosbeck, brucehoult, rbar, johnrusso, simoncook, sabuasal, niosHD, kito-cheng, shiva0217, zzheng, edward-jones, mgrang, rogfer01, llvm-commits

Differential Revision: https://reviews.llvm.org/D48411

llvm-svn: 338047

1 files changed, 11 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/RISCV/interrupt-attr-invalid.ll b/llvm/test/CodeGen/RISCV/interrupt-attr-invalid.ll
new file mode 100644
index 00000000000..bddca8af746
--- /dev/null
+++ b/llvm/test/CodeGen/RISCV/interrupt-attr-invalid.ll
@@ -0,0 +1,11 @@
+; RUN: not llc -mtriple riscv32-unknown-elf -o - %s \
+; RUN: 2>&1 | FileCheck %s
+; RUN: not llc -mtriple riscv64-unknown-elf -o - %s \
+; RUN: 2>&1 | FileCheck %s
+
+; CHECK: LLVM ERROR: Function interrupt attribute argument not supported!
+define void @isr_user() #0 {
+  ret void
+}
+
+attributes #0 = { "interrupt"="foo" }