AMDGPU: Release the scavenged offset register during VGPR spill

[nhaehnle]

Summary

This fixes a crash where subsequent spills would be unable to scavenge
a register. In particular, it fixes a crash in piglit's
spec@glsl-1.50@execution@geometry@max-input-components (the test still
has a shader that fails to compile because of too many SGPR spills, but
at least it doesn't crash any more).

This is a candidate for the release branch.

[arsenm]

LGTM with the minor test adjustments

test/CodeGen/AMDGPU/spill-scavenge-offset.ll

1 ↗

(On Diff #45911)

You don't need the -mcpu here. Also this should be run with -verify-machineinstrs, and there should be a second VI run line.

llvm/trunk/lib/Target/AMDGPU/SIRegisterInfo.cpp

void SIRegisterInfo::buildScratchLoadStore(MachineBasicBlock::iterator MI,
   const MachineFunction *MF = MI->getParent()->getParent();
   const SIInstrInfo *TII =
       static_cast<const SIInstrInfo *>(MF->getSubtarget().getInstrInfo());
   LLVMContext &Ctx = MF->getFunction()->getContext();
   DebugLoc DL = MI->getDebugLoc();
   bool IsLoad = TII->get(LoadStoreOp).mayLoad();
 
   bool RanOutOfSGPRs = false;
+  bool Scavenged = false;
   unsigned SOffset = ScratchOffset;
 
   unsigned NumSubRegs = getNumSubRegsForSpillOp(MI->getOpcode());
   unsigned Size = NumSubRegs * 4;
 
   if (!isUInt<12>(Offset + Size)) {
     SOffset = RS->scavengeRegister(&AMDGPU::SGPR_32RegClass, MI, 0);
     if (SOffset == AMDGPU::NoRegister) {
       RanOutOfSGPRs = true;
       SOffset = AMDGPU::SGPR0;
+    } else {
+      Scavenged = true;
     }
     BuildMI(*MBB, MI, DL, TII->get(AMDGPU::S_ADD_U32), SOffset)
             .addReg(ScratchOffset)
             .addImm(Offset);
     Offset = 0;
   }
 
   if (RanOutOfSGPRs)
     Ctx.emitError("Ran out of SGPRs for spilling VGPRS");
 
   for (unsigned i = 0, e = NumSubRegs; i != e; ++i, Offset += 4) {
     unsigned SubReg = NumSubRegs > 1 ?
         getPhysRegSubReg(Value, &AMDGPU::VGPR_32RegClass, i) :
         Value;
 
+    unsigned SOffsetRegState = 0;
+    if (i + 1 == e && Scavenged)
+      SOffsetRegState |= RegState::Kill;
+
     BuildMI(*MBB, MI, DL, TII->get(LoadStoreOp))
       .addReg(SubReg, getDefRegState(IsLoad))
       .addReg(ScratchRsrcReg)
-      .addReg(SOffset)
+      .addReg(SOffset, SOffsetRegState)
       .addImm(Offset)
       .addImm(0) // glc
       .addImm(0) // slc
       .addImm(0) // tfe
       .addReg(Value, RegState::Implicit | getDefRegState(IsLoad))
       .setMemRefs(MI->memoperands_begin(), MI->memoperands_end());
   }
 }

llvm/trunk/test/CodeGen/AMDGPU/spill-scavenge-offset.ll

+; RUN: llc -march=amdgcn -mcpu=verde < %s | FileCheck %s
+; RUN: llc -march=amdgcn -mcpu=tonga < %s | FileCheck %s
+
+; When the offset of VGPR spills into scratch space gets too large, an additional SGPR
+; is used to calculate the scratch load/store address. Make sure that this
+; mechanism works even when many spills happen.
+
+; Just test that it compiles successfully.
+; CHECK-LABEL: test
+define void @test(<1280 x i32> addrspace(1)* %out, <1280 x i32> addrspace(1)* %in,
+                  <96 x i32> addrspace(1)* %sdata_out, <96 x i32> %sdata_in) {
+entry:
+  %tid = call i32 @llvm.SI.tid() nounwind readnone
+
+  %aptr = getelementptr <1280 x i32>, <1280 x i32> addrspace(1)* %in, i32 %tid
+  %a = load <1280 x i32>, <1280 x i32> addrspace(1)* %aptr
+
+; mark most VGPR registers as used to increase register pressure
+  call void asm sideeffect "", "~{VGPR4},~{VGPR8},~{VGPR12},~{VGPR16},~{VGPR20},~{VGPR24},~{VGPR28},~{VGPR32}" ()
+  call void asm sideeffect "", "~{VGPR36},~{VGPR40},~{VGPR44},~{VGPR48},~{VGPR52},~{VGPR56},~{VGPR60},~{VGPR64}" ()
+  call void asm sideeffect "", "~{VGPR68},~{VGPR72},~{VGPR76},~{VGPR80},~{VGPR84},~{VGPR88},~{VGPR92},~{VGPR96}" ()
+  call void asm sideeffect "", "~{VGPR100},~{VGPR104},~{VGPR108},~{VGPR112},~{VGPR116},~{VGPR120},~{VGPR124},~{VGPR128}" ()
+  call void asm sideeffect "", "~{VGPR132},~{VGPR136},~{VGPR140},~{VGPR144},~{VGPR148},~{VGPR152},~{VGPR156},~{VGPR160}" ()
+  call void asm sideeffect "", "~{VGPR164},~{VGPR168},~{VGPR172},~{VGPR176},~{VGPR180},~{VGPR184},~{VGPR188},~{VGPR192}" ()
+  call void asm sideeffect "", "~{VGPR196},~{VGPR200},~{VGPR204},~{VGPR208},~{VGPR212},~{VGPR216},~{VGPR220},~{VGPR224}" ()
+
+  %outptr = getelementptr <1280 x i32>, <1280 x i32> addrspace(1)* %in, i32 %tid
+  store <1280 x i32> %a, <1280 x i32> addrspace(1)* %outptr
+
+  ret void
+}
+
+declare i32 @llvm.SI.tid() nounwind readnone