[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, 30 insertions, 0 deletions

diff --git a/llvm/lib/Target/RISCV/RISCVFrameLowering.cpp b/llvm/lib/Target/RISCV/RISCVFrameLowering.cpp
index 3dc1e3dbb27..a816028f9d8 100644
--- a/llvm/lib/Target/RISCV/RISCVFrameLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVFrameLowering.cpp
@@ -212,6 +212,36 @@ void RISCVFrameLowering::determineCalleeSaves(MachineFunction &MF,
     SavedRegs.set(RISCV::X1);
     SavedRegs.set(RISCV::X8);
   }
+
+  // If interrupt is enabled and there are calls in the handler,
+  // unconditionally save all Caller-saved registers and
+  // all FP registers, regardless whether they are used.
+  MachineFrameInfo &MFI = MF.getFrameInfo();
+
+  if (MF.getFunction().hasFnAttribute("interrupt") && MFI.hasCalls()) {
+
+    static const MCPhysReg CSRegs[] = { RISCV::X1,      /* ra */
+      RISCV::X5, RISCV::X6, RISCV::X7,                  /* t0-t2 */
+      RISCV::X10, RISCV::X11,                           /* a0-a1, a2-a7 */
+      RISCV::X12, RISCV::X13, RISCV::X14, RISCV::X15, RISCV::X16, RISCV::X17,
+      RISCV::X28, RISCV::X29, RISCV::X30, RISCV::X31, 0 /* t3-t6 */
+    };
+
+    for (unsigned i = 0; CSRegs[i]; ++i)
+      SavedRegs.set(CSRegs[i]);
+
+    if (MF.getSubtarget<RISCVSubtarget>().hasStdExtD() ||
+        MF.getSubtarget<RISCVSubtarget>().hasStdExtF()) {
+
+      // If interrupt is enabled, this list contains all FP registers.
+      const MCPhysReg * Regs = MF.getRegInfo().getCalleeSavedRegs();
+
+      for (unsigned i = 0; Regs[i]; ++i)
+        if (RISCV::FPR32RegClass.contains(Regs[i]) ||
+            RISCV::FPR64RegClass.contains(Regs[i]))
+          SavedRegs.set(Regs[i]);
+    }
+  }
 }
 
 void RISCVFrameLowering::processFunctionBeforeFrameFinalized(