Merging r368300:

zmodem · zmodem · commit 82330f1c510c · 2019-08-14T12:59:17.000Z
------------------------------------------------------------------------ r368300 | lenary | 2019-08-08 16:40:54 +0200 (Thu, 08 Aug 2019) | 18 lines [RISCV] Minimal stack realignment support Summary: Currently the RISC-V backend does not realign the stack. This can be an issue even for the RV32I/RV64I ABIs (where the stack is 16-byte aligned), though is rare. It will be much more comment with RV32E (though the alignment requirements for common data types remain under-documented...). This patch adds minimal support for stack realignment. It should cope with large realignments. It will error out if the stack needs realignment and variable sized objects are present. It feels like a lot of the code like getFrameIndexReference and determineFrameLayout could be refactored somehow, as right now it feels fiddly and brittle. We also seem to allocate a lot more memory than GCC does for equivalent C code. Reviewers: asb Reviewed By: asb Subscribers: wwei, jrtc27, s.egerton, MaskRay, Jim, lenary, hiraditya, rbar, johnrusso, simoncook, apazos, sabuasal, niosHD, kito-cheng, shiva0217, zzheng, edward-jones, rogfer01, MartinMosbeck, brucehoult, the_o, rkruppe, PkmX, jocewei, psnobl, benna, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D62007 ------------------------------------------------------------------------ llvm-svn: 368846
diff --git a/llvm/lib/Target/RISCV/RISCVFrameLowering.cpp b/llvm/lib/Target/RISCV/RISCVFrameLowering.cpp
@@ -40,8 +40,16 @@ void RISCVFrameLowering::determineFrameLayout(MachineFunction &MF) const {
   uint64_t FrameSize = MFI.getStackSize();
 
   // Get the alignment.
-  uint64_t StackAlign = RI->needsStackRealignment(MF) ? MFI.getMaxAlignment()
-                                                      : getStackAlignment();
+  unsigned StackAlign = getStackAlignment();
+  if (RI->needsStackRealignment(MF)) {
+    unsigned MaxStackAlign = std::max(StackAlign, MFI.getMaxAlignment());
+    FrameSize += (MaxStackAlign - StackAlign);
+    StackAlign = MaxStackAlign;
+  }
+
+  // Set Max Call Frame Size
+  uint64_t MaxCallSize = alignTo(MFI.getMaxCallFrameSize(), StackAlign);
+  MFI.setMaxCallFrameSize(MaxCallSize);
 
   // Make sure the frame is aligned.
   FrameSize = alignTo(FrameSize, StackAlign);
@@ -101,6 +109,12 @@ void RISCVFrameLowering::emitPrologue(MachineFunction &MF,
   const RISCVInstrInfo *TII = STI.getInstrInfo();
   MachineBasicBlock::iterator MBBI = MBB.begin();
 
+  if (RI->needsStackRealignment(MF) && MFI.hasVarSizedObjects()) {
+    report_fatal_error(
+        "RISC-V backend can't currently handle functions that need stack "
+        "realignment and have variable sized objects");
+  }
+
   unsigned FPReg = getFPReg(STI);
   unsigned SPReg = getSPReg(STI);
 
@@ -158,6 +172,29 @@ void RISCVFrameLowering::emitPrologue(MachineFunction &MF,
         nullptr, RI->getDwarfRegNum(FPReg, true), 0));
     BuildMI(MBB, MBBI, DL, TII->get(TargetOpcode::CFI_INSTRUCTION))
         .addCFIIndex(CFIIndex);
+
+    // Realign Stack
+    const RISCVRegisterInfo *RI = STI.getRegisterInfo();
+    if (RI->needsStackRealignment(MF)) {
+      unsigned MaxAlignment = MFI.getMaxAlignment();
+
+      const RISCVInstrInfo *TII = STI.getInstrInfo();
+      if (isInt<12>(-(int)MaxAlignment)) {
+        BuildMI(MBB, MBBI, DL, TII->get(RISCV::ANDI), SPReg)
+            .addReg(SPReg)
+            .addImm(-(int)MaxAlignment);
+      } else {
+        unsigned ShiftAmount = countTrailingZeros(MaxAlignment);
+        unsigned VR =
+            MF.getRegInfo().createVirtualRegister(&RISCV::GPRRegClass);
+        BuildMI(MBB, MBBI, DL, TII->get(RISCV::SRLI), VR)
+            .addReg(SPReg)
+            .addImm(ShiftAmount);
+        BuildMI(MBB, MBBI, DL, TII->get(RISCV::SLLI), SPReg)
+            .addReg(VR)
+            .addImm(ShiftAmount);
+      }
+    }
   }
 }
 
@@ -257,6 +294,13 @@ int RISCVFrameLowering::getFrameIndexReference(const MachineFunction &MF,
   if (FI >= MinCSFI && FI <= MaxCSFI) {
     FrameReg = RISCV::X2;
     Offset += MF.getFrameInfo().getStackSize();
+  } else if (RI->needsStackRealignment(MF)) {
+    assert(!MFI.hasVarSizedObjects() &&
+           "Unexpected combination of stack realignment and varsized objects");
+    // If the stack was realigned, the frame pointer is set in order to allow
+    // SP to be restored, but we still access stack objects using SP.
+    FrameReg = RISCV::X2;
+    Offset += MF.getFrameInfo().getStackSize();
   } else {
     FrameReg = RI->getFrameRegister(MF);
     if (hasFP(MF))
diff --git a/llvm/test/CodeGen/RISCV/stack-realignment-unsupported.ll b/llvm/test/CodeGen/RISCV/stack-realignment-unsupported.ll
@@ -0,0 +1,13 @@
+; RUN: not llc -mtriple=riscv32 < %s 2>&1 | FileCheck %s
+; RUN: not llc -mtriple=riscv64 < %s 2>&1 | FileCheck %s
+
+; CHECK: LLVM ERROR: RISC-V backend can't currently handle functions that need stack realignment and have variable sized objects
+
+declare void @callee(i8*, i32*)
+
+define void @caller(i32 %n) nounwind {
+  %1 = alloca i8, i32 %n
+  %2 = alloca i32, align 64
+  call void @callee(i8* %1, i32 *%2)
+  ret void
+}
diff --git a/llvm/test/CodeGen/RISCV/stack-realignment.ll b/llvm/test/CodeGen/RISCV/stack-realignment.ll
