[RISCV] Add coverage for immediate sinking in switch vs branch cases

This come up in the context of pr 108889.  We always end up sinking
the value in the phi if we dispatched via a switch, but not if we'd
dispatched via a branch.  This is purely an artifact of current
lowering.

Author: preames

llvm/test/CodeGen/RISCV/machine-sink-load-immediate.ll

@@ -205,3 +205,174 @@ bb5:                                              ; preds = %bb2, %bb
   %i6 = phi i32 [ %i4, %bb2 ], [ 13, %bb ]
   ret i32 %i6
 }
+
+
+; For switches, the values feeding the phi are always sunk into the
+; target blocks as the IR syntax requires the intermediate block and
+; DAG lowers it in the immediate predecessor of the phi.
+define signext i32 @switch_dispatch(i8 %a) {
+; CHECK-LABEL: switch_dispatch:
+; CHECK:       # %bb.0: # %bb
+; CHECK-NEXT:    addi sp, sp, -16
+; CHECK-NEXT:    .cfi_def_cfa_offset 16
+; CHECK-NEXT:    sd ra, 8(sp) # 8-byte Folded Spill
+; CHECK-NEXT:    sd s0, 0(sp) # 8-byte Folded Spill
+; CHECK-NEXT:    .cfi_offset ra, -8
+; CHECK-NEXT:    .cfi_offset s0, -16
+; CHECK-NEXT:    andi a0, a0, 255
+; CHECK-NEXT:    li a1, 31
+; CHECK-NEXT:    blt a1, a0, .LBB2_5
+; CHECK-NEXT:  # %bb.1: # %bb
+; CHECK-NEXT:    beqz a0, .LBB2_10
+; CHECK-NEXT:  # %bb.2: # %bb
+; CHECK-NEXT:    li a1, 12
+; CHECK-NEXT:    beq a0, a1, .LBB2_11
+; CHECK-NEXT:  # %bb.3: # %bb
+; CHECK-NEXT:    li a1, 13
+; CHECK-NEXT:    bne a0, a1, .LBB2_9
+; CHECK-NEXT:  # %bb.4: # %case.4
+; CHECK-NEXT:    li s0, 644
+; CHECK-NEXT:    j .LBB2_13
+; CHECK-NEXT:  .LBB2_5: # %bb
+; CHECK-NEXT:    li a1, 234
+; CHECK-NEXT:    beq a0, a1, .LBB2_9
+; CHECK-NEXT:  # %bb.6: # %bb
+; CHECK-NEXT:    li a1, 70
+; CHECK-NEXT:    beq a0, a1, .LBB2_12
+; CHECK-NEXT:  # %bb.7: # %bb
+; CHECK-NEXT:    li a1, 32
+; CHECK-NEXT:    bne a0, a1, .LBB2_9
+; CHECK-NEXT:  # %bb.8: # %case.0
+; CHECK-NEXT:    li s0, 13
+; CHECK-NEXT:    j .LBB2_13
+; CHECK-NEXT:  .LBB2_9: # %case.default
+; CHECK-NEXT:    li s0, 23
+; CHECK-NEXT:    j .LBB2_13
+; CHECK-NEXT:  .LBB2_10: # %case.5
+; CHECK-NEXT:    li s0, 54
+; CHECK-NEXT:    j .LBB2_13
+; CHECK-NEXT:  .LBB2_11: # %case.1
+; CHECK-NEXT:    li s0, 53
+; CHECK-NEXT:    j .LBB2_13
+; CHECK-NEXT:  .LBB2_12: # %case.2
+; CHECK-NEXT:    li s0, 33
+; CHECK-NEXT:  .LBB2_13: # %merge
+; CHECK-NEXT:    mv a0, s0
+; CHECK-NEXT:    call use
+; CHECK-NEXT:    mv a0, s0
+; CHECK-NEXT:    ld ra, 8(sp) # 8-byte Folded Reload
+; CHECK-NEXT:    ld s0, 0(sp) # 8-byte Folded Reload
+; CHECK-NEXT:    .cfi_restore ra
+; CHECK-NEXT:    .cfi_restore s0
+; CHECK-NEXT:    addi sp, sp, 16
+; CHECK-NEXT:    .cfi_def_cfa_offset 0
+; CHECK-NEXT:    ret
+bb:
+  switch i8 %a, label %case.default [
+    i8 32, label %case.0
+    i8 12, label %case.1
+    i8 70, label %case.2
+    i8 -22, label %case.3
+    i8 13, label %case.4
+    i8 0, label %case.5
+  ]
+
+case.0:
+  br label %merge
+case.1:
+  br label %merge
+case.2:
+  br label %merge
+case.3:
+  br label %merge
+case.4:
+  br label %merge
+case.5:
+  br label %merge
+case.default:
+  br label %merge
+
+merge:
+  %res = phi i32 [ 23, %case.default ], [ 13, %case.0 ], [ 53, %case.1 ], [ 33, %case.2 ], [ 23, %case.3 ], [ 644, %case.4 ], [ 54, %case.5 ]
+  call void @use(i32 %res)
+  ret i32 %res
+}
+
+; Same as for the switch, but written via manual branching.
+define signext i32 @branch_dispatch(i8 %a) {
+; CHECK-LABEL: branch_dispatch:
+; CHECK:       # %bb.0: # %case.0
+; CHECK-NEXT:    addi sp, sp, -16
+; CHECK-NEXT:    .cfi_def_cfa_offset 16
+; CHECK-NEXT:    sd ra, 8(sp) # 8-byte Folded Spill
+; CHECK-NEXT:    sd s0, 0(sp) # 8-byte Folded Spill
+; CHECK-NEXT:    .cfi_offset ra, -8
+; CHECK-NEXT:    .cfi_offset s0, -16
+; CHECK-NEXT:    andi a0, a0, 255
+; CHECK-NEXT:    li a1, 32
+; CHECK-NEXT:    li s0, 13
+; CHECK-NEXT:    beq a0, a1, .LBB3_8
+; CHECK-NEXT:  # %bb.1: # %case.1
+; CHECK-NEXT:    li a1, 12
+; CHECK-NEXT:    li s0, 53
+; CHECK-NEXT:    beq a0, a1, .LBB3_8
+; CHECK-NEXT:  # %bb.2: # %case.2
+; CHECK-NEXT:    li a1, 70
+; CHECK-NEXT:    li s0, 33
+; CHECK-NEXT:    beq a0, a1, .LBB3_8
+; CHECK-NEXT:  # %bb.3: # %case.3
+; CHECK-NEXT:    li a1, 234
+; CHECK-NEXT:    li s0, 23
+; CHECK-NEXT:    beq a0, a1, .LBB3_8
+; CHECK-NEXT:  # %bb.4: # %case.4
+; CHECK-NEXT:    beqz a0, .LBB3_7
+; CHECK-NEXT:  # %bb.5: # %case.5
+; CHECK-NEXT:    li a1, 5
+; CHECK-NEXT:    li s0, 54
+; CHECK-NEXT:    beq a0, a1, .LBB3_8
+; CHECK-NEXT:  # %bb.6: # %case.default
+; CHECK-NEXT:    li s0, 23
+; CHECK-NEXT:    j .LBB3_8
+; CHECK-NEXT:  .LBB3_7:
+; CHECK-NEXT:    li s0, 644
+; CHECK-NEXT:  .LBB3_8: # %merge
+; CHECK-NEXT:    mv a0, s0
+; CHECK-NEXT:    call use
+; CHECK-NEXT:    mv a0, s0
+; CHECK-NEXT:    ld ra, 8(sp) # 8-byte Folded Reload
+; CHECK-NEXT:    ld s0, 0(sp) # 8-byte Folded Reload
+; CHECK-NEXT:    .cfi_restore ra
+; CHECK-NEXT:    .cfi_restore s0
+; CHECK-NEXT:    addi sp, sp, 16
+; CHECK-NEXT:    .cfi_def_cfa_offset 0
+; CHECK-NEXT:    ret
+case.0:
+  %c0 = icmp ne i8 %a, 32
+  br i1 %c0, label %case.1, label %merge
+case.1:
+  %c1 = icmp ne i8 %a, 12
+  br i1 %c1, label %case.2, label %merge
+case.2:
+  %c2 = icmp ne i8 %a, 70
+  br i1 %c2, label %case.3, label %merge
+case.3:
+  %c3 = icmp ne i8 %a, -22
+  br i1 %c3, label %case.4, label %merge
+case.4:
+  %c4 = icmp ne i8 %a, 0
+  br i1 %c4, label %case.5, label %merge
+case.5:
+  %c5 = icmp ne i8 %a, 5
+  br i1 %c5, label %case.default, label %merge
+case.default:
+  br label %merge
+
+merge:
+  %res = phi i32 [ 23, %case.default ], [ 13, %case.0 ], [ 53, %case.1 ], [ 33, %case.2 ], [ 23, %case.3 ], [ 644, %case.4 ], [ 54, %case.5 ]
+  call void @use(i32 %res)
+  ret i32 %res
+}
+
+
+declare void @use(i32)
+