[AMDGPU] Fix SIFoldOperands crash with clamp

[rampitec]

Summary

Fixes bug #33302. Pass did not account that Src1 of max instruction can be an immediate.

[arsenm]

LGTM

lib/Target/AMDGPU/SIFoldOperands.cpp

const MachineOperand *SIFoldOperands::isClamp(const MachineInstr &MI) const {
   case AMDGPU::V_MAX_F16_e64:
   case AMDGPU::V_MAX_F64: {
     if (!TII->getNamedOperand(MI, AMDGPU::OpName::clamp)->getImm())
       return nullptr;
 
     // Make sure sources are identical.
     const MachineOperand *Src0 = TII->getNamedOperand(MI, AMDGPU::OpName::src0);
     const MachineOperand *Src1 = TII->getNamedOperand(MI, AMDGPU::OpName::src1);
-    if (!Src0->isReg() || Src0->getSubReg() != Src1->getSubReg() ||
+    if (!Src0->isReg() || !Src1->isReg() ||
+        Src0->getSubReg() != Src1->getSubReg() ||
         Src0->getSubReg() != AMDGPU::NoSubRegister)
       return nullptr;
 
     // Can't fold up if we have modifiers.
     if (TII->hasModifiersSet(MI, AMDGPU::OpName::src0_modifiers) ||
         TII->hasModifiersSet(MI, AMDGPU::OpName::src1_modifiers) ||
         TII->hasModifiersSet(MI, AMDGPU::OpName::omod))
       return nullptr;

test/CodeGen/AMDGPU/clamp-omod-special-case.mir

--- |
   define amdgpu_ps void @v_omod_add_omod_already_set_f32() #0 {
     ret void
   }
 
   define amdgpu_ps void @v_omod_add_clamp_already_set_f32() #0 {
     ret void
   }
 
+  define amdgpu_ps void @v_max_reg_imm_f32() #0 {
+    ret void
+  }
+
   attributes #0 = { nounwind "no-signed-zeros-fp-math"="false" }
 
 ...
 ---
 # GCN-LABEL: name: v_max_self_clamp_not_set_f32
 # GCN: %20 = V_ADD_F32_e64 0, killed %17, 0, 1065353216, 0, 0, implicit %exec
 # GCN-NEXT: %21 = V_MAX_F32_e64 0, killed %20, 0, killed %20, 0, 0, implicit %exec
 
bb.0 (%ir-block.0):
     %18 = COPY %26
     %17 = BUFFER_LOAD_DWORD_ADDR64 %26, killed %13, 0, 0, 0, 0, 0, implicit %exec
     %20 = V_ADD_F32_e64 0, killed %17, 0, 1065353216, 0, 0, implicit %exec
     %21 = V_ADD_F32_e64 0, killed %20, 0, killed %20, 1, 0, implicit %exec
     BUFFER_STORE_DWORD_ADDR64 killed %21, %26, killed %16, 0, 0, 0, 0, 0, implicit %exec
     S_ENDPGM
 
 ...
+---
+
+# Pass used to crash with immediate second operand of max
+name:            v_max_reg_imm_f32
+tracksRegLiveness: true
+registers:
+  - { id: 0, class: vgpr_32 }
+  - { id: 1, class: vgpr_32 }
+body:             |
+  bb.0 (%ir-block.0):
+    liveins: %vgpr0
+
+    %0 = COPY %vgpr0
+    %1 = V_MAX_F32_e64 0, killed %0, 0, 1056964608, 1, 0, implicit %exec
+
+...