[AMDGPU] Fix crash in SIOptimizeExecMaskingPreRA

[foad]

Summary

When folding a COPY of exec into another COPY, the call to
TII->isOperandLegal would crash because COPYs don't have defined
register classes for their operands.

[arsenm]

Could also use a MIR test

llvm/lib/Target/AMDGPU/SIOptimizeExecMaskingPreRA.cpp

425

A COPY isn't the only case where this happens though

427

Newline is redundant here

[foad]

llvm/lib/Target/AMDGPU/SIOptimizeExecMaskingPreRA.cpp

425

I was wondering about that. How do all the existing callers of isOperandLegal manage not to hit this assertion?

llc: lib/Target/AMDGPU/SIInstrInfo.cpp:5013: bool llvm::SIInstrInfo::isOperandLegal(const llvm::MachineInstr &, unsigned int, const llvm::MachineOperand *) const: Assertion `DefinedRC' failed.

[alex-t]

llvm/lib/Target/AMDGPU/SIOptimizeExecMaskingPreRA.cpp

425

In fact, the operand always legal in COPY. So, SIInstrInfo::isOperandLegal may just return true for the case where no defined RC and the instruction opcode is COPY

[alex-t]

LGTM if we do not want to change the COPY processing in the SIInstrInfo::isOperandLegal

[foad]

Handle any instruction without a defined RC, not just COPY.

[foad]

In D122737#3422970, @alex-t wrote:

LGTM if we do not want to change the COPY processing in the SIInstrInfo::isOperandLegal

How about this? As @arsenm pointed out this can happen for other instructions, not just COPY, so I handle them all the same way.

llvm/lib/Target/AMDGPU/SIOptimizeExecMaskingPreRA.cpp

for (auto I = MBB.rbegin(), E = MBB.rend(); I != E
 
       Register SavedExec = I->getOperand(0).getReg();
       if (SavedExec.isVirtual() && MRI->hasOneNonDBGUse(SavedExec)) {
         MachineInstr *SingleExecUser = &*MRI->use_instr_nodbg_begin(SavedExec);
         int Idx = SingleExecUser->findRegisterUseOperandIdx(SavedExec);
         assert(Idx != -1);
         if (SingleExecUser->getParent() == I->getParent() &&
             !SingleExecUser->getOperand(Idx).isImplicit() &&
-            TII->isOperandLegal(*SingleExecUser, Idx, &I->getOperand(1))) {
+            (SingleExecUser->isCopy() ||
+             TII->isOperandLegal(*SingleExecUser, Idx, &I->getOperand(1)))) {
           LLVM_DEBUG(dbgs() << "Redundant EXEC COPY: " << *I << '\n');
           LIS->RemoveMachineInstrFromMaps(*I);
           I->eraseFromParent();
           MRI->replaceRegWith(SavedExec, ExecReg);
           LIS->removeInterval(SavedExec);
           Changed = true;
         }
       }
       break;

llvm/test/CodeGen/AMDGPU/atomic-optimizer-strict-wqm.ll

+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -march=amdgcn -mcpu=gfx1010 -amdgpu-atomic-optimizations < %s | FileCheck %s -check-prefixes=GFX10
+
+declare void @llvm.amdgcn.exp.f32(i32 immarg, i32 immarg, float, float, float, float, i1 immarg, i1 immarg)
+declare i32 @llvm.amdgcn.raw.buffer.atomic.and.i32(i32, <4 x i32>, i32, i32, i32 immarg)
+declare float @llvm.amdgcn.strict.wqm.f32(float)
+
+define amdgpu_ps void @main(i32 %arg) {
+; GFX10-LABEL: main:
+; GFX10:       ; %bb.0: ; %bb
+; GFX10-NEXT:    v_cmp_eq_u32_e32 vcc_lo, 1, v0
+; GFX10-NEXT:    v_mov_b32_e32 v0, 0
+; GFX10-NEXT:    s_mov_b32 s1, exec_lo
+; GFX10-NEXT:    s_mov_b32 s4, 0
+; GFX10-NEXT:    s_mov_b32 s2, 0
+; GFX10-NEXT:    s_branch .LBB0_2
+; GFX10-NEXT:  .LBB0_1: ; %Flow
+; GFX10-NEXT:    ; in Loop: Header=BB0_2 Depth=1
+; GFX10-NEXT:    s_waitcnt_depctr 0xffe3
+; GFX10-NEXT:    s_or_b32 exec_lo, exec_lo, s3
+; GFX10-NEXT:    s_andn2_b32 exec_lo, exec_lo, s2
+; GFX10-NEXT:    s_cbranch_execz .LBB0_5
+; GFX10-NEXT:  .LBB0_2: ; %bb4
+; GFX10-NEXT:    ; =>This Inner Loop Header: Depth=1
+; GFX10-NEXT:    s_and_b32 s0, exec_lo, vcc_lo
+; GFX10-NEXT:    s_or_b32 s2, s0, s2
+; GFX10-NEXT:    s_and_saveexec_b32 s3, s1
+; GFX10-NEXT:    s_cbranch_execz .LBB0_1
+; GFX10-NEXT:  ; %bb.3: ; in Loop: Header=BB0_2 Depth=1
+; GFX10-NEXT:    v_mbcnt_lo_u32_b32 v1, exec_lo, 0
+; GFX10-NEXT:    v_cmp_eq_u32_e64 s0, 0, v1
+; GFX10-NEXT:    s_and_b32 exec_lo, exec_lo, s0
+; GFX10-NEXT:    s_cbranch_execz .LBB0_1
+; GFX10-NEXT:  ; %bb.4: ; in Loop: Header=BB0_2 Depth=1
+; GFX10-NEXT:    s_mov_b32 s5, s4
+; GFX10-NEXT:    s_mov_b32 s6, s4
+; GFX10-NEXT:    s_mov_b32 s7, s4
+; GFX10-NEXT:    buffer_atomic_and v0, off, s[4:7], 0
+; GFX10-NEXT:    s_branch .LBB0_1
+; GFX10-NEXT:  .LBB0_5: ; %bb8
+; GFX10-NEXT:    s_or_b32 exec_lo, exec_lo, s2
+; GFX10-NEXT:    s_mov_b32 s0, 0
+; GFX10-NEXT:    v_mov_b32_e32 v1, 0
+; GFX10-NEXT:    v_mov_b32_e32 v0, s0
+; GFX10-NEXT:    exp mrt0 off, off, off, off
+; GFX10-NEXT:    s_endpgm
+bb:
+  br label %bb4
+
+bb4:
+  %i5 = call i32 @llvm.amdgcn.raw.buffer.atomic.and.i32(i32 0, <4 x i32> zeroinitializer, i32 0, i32 0, i32 0)
+  %i7 = icmp eq i32 %arg, 1
+  br i1 %i7, label %bb8, label %bb4
+
+bb8:
+  %i9 = call float @llvm.amdgcn.strict.wqm.f32(float 0.0)
+  call void @llvm.amdgcn.exp.f32(i32 0, i32 0, float %i9, float 0.0, float 0.0, float 0.0, i1 false, i1 false)
+  ret void
+}